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“I have some money, what do I need to buy?” – Well, let’s hit the brakes, first.
Let’s get some understanding of what’s going on with the car. Let’s go with the assumption that everyone has a stiff chassis (sub-frame connectors (SFC)), and good working suspension parts to begin with.
TERMS: Roll Center (RC): Cars have two roll centers - front suspension & the rear suspension. They act as pivot points. When a car experiences body rolls during cornering, everything above that pivot point rotates towards the outside of the corner, and everything below the pivot point rotates the opposite direction, towards the inside of the corner. Center of Gravity (CG): A calculation of the car’s mass to determine where the center is. When a car is cornering, forces act on the car’s Center of Gravity. Moment Arm: The distance between the height of the CG & the height of each Roll Center is called the “Moment Arm.” Think of it as a lever. The farther apart the CG & roll center are, then the more leverage the CG has over the roll center to make the car roll. Weight transfer: The car’s weight mass at the CG is acting on the roll & pivot axis of the car and applying “Force” when the driver tries to get the car to stop, turn or accelerate. Roll Angle: The amount the car “rolls” on its roll axis (side-to-side) in cornering. Pitch Angle: is the amount the car “rotates” front to back under braking or acceleration. Dive: The front suspension compressing under braking & cornering forces. Squat: The car planting the rear end on launch or under acceleration Roll: Side to side body rotation, or body roll. Pitch: Fore & aft body rotation. When the front end dives & back end rises under braking, or when the front end rises & the back end squats under acceleration. Understeer: The front tires have lost grip and the car is going towards the outside of the corner nose first (push). Oversteer: The rear tires have lost grip and the car is going towards the outside of the corner tail first (loose).
Contact patch is the highest priority. This is the overarching theme.This is why dampahhs (shocks/struts) and rubbahhs (tires and their compounds) are critical. You just have to pay the price. Shocks help keep the contact patch. Before we go too far with parts, let’s look at the car and the suspension philosophy.
For cars to handle well, the suspension needs to travel or work (it can’t be flat). It has to roll and pitch. It is dangerous to have a car that rolls a lot, and pitches a lot. So we need to find a balance. There are two common strategies: let the car roll a lot and pitch a little (conventional), OR, pitch a lot and roll a little (modern). The conventional route has stiff front springs and soft rear springs; and small sway bars to allow the car to roll: low travel/ high roll. The modern route has soft front springs and stiff rear springs; and big sway bar in front with smaller one in rear: high travel/low roll. Both these strategies are effective. Soft and stiff are relative terms: total difference in dive could be as little as 2” or less; total difference in roll angle 2*.
The front tires need force, from weight transfer on corner entry, to provide front tire grip. Too little & the car pushes (understeer), too much & the car is loose on entry (oversteer). The rear tires need force, from weight transfer on corner exit, to provide rear tire grip. Too little & the car is loose, too much & the car pushes on exit.
Our cars suffer from:
- the static roll center height is too low, causing too much roll angle
- the dynamic roll center height in dive and roll is too low, causing even more roll angle
- front suspension geometry has a jacking effect and a higher front roll angle vs. rear
- rear roll center was too high
Roll Couple Example: Here are some examples using a 3500# car with 55% front weight to provide some conceptualization:
If the CG is 20” high, and the front roll center is 1” above ground, the car has 55% of the 3500# weight with 19” of leverage to roll the front of the car.
If the CG is 20” high, and the rear roll center is 11” above ground, the car has 45% of the 3500# weight with 9” of leverage to roll the rear of the car.
* Rolling the car that much more in the front overloads the outside front tire & under- utilizes the inside front tire when cornering.
If you lowered the car 2” the CG drops 2”. The front roll center probably moved too, but it’s not linear as it is based on A-arm angles. Let’s say it dropped 1” in the front to 0” above ground and the rear stayed the same at 11”. Now …
If the CG is 18” high, and the front roll center is 0” above ground, the car has 55% of the 3500# weight with 18” of leverage to roll the front of the car.
If the CG is 18” high, and the rear roll center is 11” above ground, the car has 45% of the 3500# weight with 7” of leverage to roll the rear of the car.
* The front now rolls over less & the rear too, making the car run “flatter” - not flat, just less roll angle which works the inside tires better.
So it is very important to know your vehicle, and to minimize the moment arm (leverage) with both front and rear (roll couple) in mind. Getting the front & rear of the car to roll similar is desired. Getting them to roll the same is not, because the goal is: To have optimum grip on all tires and disengage the inside rear tire (to a degree) to turn well, then re-engage the inside rear tire (to a higher degree) for maximum forward bite on exit (Dean would advocate progressive rate rear springs, here). So, on entry & mid-corner, the car needs to roll slightly less in the front to keep both front tires engaged for optimum front end grip (more dive), while allowing the car to roll slightly more in the rear to disengage the inside rear tire, to a small degree, to turn better. For optimal exit, the car will have more roll in the front & less in the rear to re-engage the inside rear tire to a higher degree than it was on entry & exit, for maximum forward bite (traction) on exit.
Going back to the roll couple example, by lowering the car, the front roll center goes to ground level (even below ground under braking-dive). What is needed is to raise the front roll center in order to reduce the moment arm (leverage). Drop spindles are the best method; they can raise 2”, but they are scarce for our cars. Extended ball joints can raise the front RC by 1” - #1. About the rear RC, you can weld-on a bracket to the axle-side panhard bar mount - #2; lowering the attachment point, which lowers the rear RC (small incremental changes, here). In this way, you are decreasing the front roll leverage, and slightly increasing the rear roll leverage so that they are closer together – a better roll couple. These two modifications are the two best changes to make (whether lowered or not), AND they do not cost a whole lot of money. By mitigating the forces applied to the roll couple, you make all your other parts work under less stress/force/leverage. This increases the effectiveness of all the other parts.
By lowering the CG 2”, and using ext. BJ (+1” RC) and PHB mount (-1” RC), the car would have 17” of leverage to roll the front; and, 8” of leverage to roll the rear. These are example numbers, not fact. But that’s a very good outcome for such little money, which also increases the effectiveness of all the other parts.
Lowering the CG helps lessen the moment arm (as in the example). But if we can’t raise the RC out of the weeds, it may be better to raise the car. A bigger sway bar would be necessary to limit the moment arm. Ride height is a tool in the tool kit, not a goal in and of itself.
Now that we have attempted to optimize the roll couple, then we can focus on springs, shocks, and sway bars as tools to control the weight transfer and keep all four contact patches optimal. We tune a car to find the optimum balance of grip. Grip equals speed.
Now the conventional or modern approach needs to be decided upon. High roll/ less pitch (conventional), or low roll/more pitch (modern). Again, these are relative to each other, not extreme positions by themselves. The modern approach puts the nose on the ground (more weight xfer on the front) to provide grip to turn. The conventional approach uses more roll angle to help turn (not that it doesn’t have some pitch). The modern approach can carry more corner speed, but the conventional approach can out-brake going into the corner = two different driving styles.
The conventional will use heavier front springs and lighter sway bar; modern will use softer front spring and bigger sway bar. With a bigger sway bar, you can’t just lock up the front suspension – you need independent wheel movement. Limiting roll helps preserve tire life – better for long road courses. Softer bar with more roll heats up the tires more – better suited for AutoX. But personal driving style/preference will really dictate which to choose. Remember, you have to match the rear with the front choice.
NOW, we get to spend the money. We’re back to dampahhs and rubbahhs. Get the best, or save until you can. This includes lightweight wheels!
Unsprung weight is key to a great handling car. It greatly aids the contact patch. It makes a car more comfortable to drive (less jarring force of inertia). Lightweight and strong parts are expensive. There is no getting around it, and most people are also saving for more horsepower. This is where the rubber meets the road, and the pretenders are separated out. In my opinion, a #19-#20 17x9.5 wheel is the standard goal. If you can find drop spindles, then shoot for #18-#19 17x8’s. Then add aluminum hubs, 2 pc curved vein rotors, FSL calipers, and tubular a-arms. There is much more to be said about weight savings and other performance parts; they are listed in other threads.
I hope this aids your thought process as to how to go about making your car handle better. The best step is the roll couple, the cost is low, and it does apply to cars lowered or not.
NOW, we get to spend the money. We’re back to dampahhs and rubbahhs. Get the best, or save until you can. This includes lightweight wheels!
Unsprung weight is key to a great handling car. It greatly aids the contact patch. It makes a car more comfortable to drive (less jarring force of inertia). Lightweight and strong parts are expensive. There is no getting around it, and most people are also saving for more horsepower. This is where the rubber meets the road, and the pretenders are separated out. In my opinion, a #19-#20 17x9.5 wheel is the standard goal. If you can find drop spindles, then shoot for #18-#19 17x8’s. Then add aluminum hubs, 2 pc curved vein rotors, FSL calipers, and tubular a-arms. There is much more to be said about weight savings and other performance parts; they are listed in other threads.
I hope this aids your thought process as to how to go about making your car handle better. The best step is the roll couple, the cost is low, and it does apply to cars lowered or not.
Genuine Corvette wheels are a blessing in this arena. Either C5 wagon wheels or C4 sawblades are somewhat lightweight for their size, wide enough for good rubber and not too large in diameter.
I think 17" is the perfect balance for third gens, our cars were designed with a maximum of 16" wheels in mind, 18" wheels are far too jarring with the stock suspension let alone a stiffer aftermarket setup.
You can find sawblades and wagon wheels on Craigslist for under $500 all day long and in the end you've got a strong, semi-lightweight wheel with plenty of good performance tire options. The next logical step up in my opinion would be something like a CCW, but most people aren't willing to spend $2500 on wheels that will shave 10lbs off of their weight (although weight saving in unsprung weight make the biggest difference.
The main downside is having to use pretty large wheel spacers, which eat into the weight savings, but at least the weight is closer to the hub and not towards the outside diameter of the wheel which multiplies as rotational mass.
I think 17" is the perfect balance for third gens,
I agree, and some sidewall is beneficial at high speeds.
My point was that the important two steps don't require all that much money:
1. Optimize roll couple
2. Work out the springs/bars/shocks.
3. Wheel Assemblies - Unsprung Weight ($$).
One can make a less than optimal choice in wheel assemblies, and still have a good handling car (provided 1 & 2). But when one starts making two less than optimal choices, it begins a snowball effect and one looses the drive/inspiration to limit weight. Once you have a big heavy wheel, why purchase expensive lightweight calipers or 2 pc rotors, etc. A big heavy wide wheel can actually have less contact patch, and can have more uneven wear due to control issues!
But if one absolutely wants an 18" wheel, I wouldn't want to say all is lost. I do think you can mitigate a less than optimal choice, but you have to be more diligent in other areas. There is room for personal preference!
I wonder if anyone has come up with a target # for wheel assemblies, then try to hit that # with different assortments.
I dislike spacers on the front, but can accept a small slip spacer on the rear - just get the right fitment! We all have to live under the financial realities. I usually do not regret buying quality.
The 3rd gens were actually designed for 15" wheels - 16" didn't even come as an option until 1984 and 1985 it was widespread. The cars were designed in the late 70's after all.
Now as someone who sells 17" wheels for the 3rd gens, it was a large project to get the right balance of weight, strength, brake clearance, and cost. For every extra lb of wheel weight (rotating and also unsprung), it is akin to adding 4lb of static weight - so a wheel weighing 5lbs each more will affect a car/truck as much as adding 80lbs of dead weight (5lbs*4*4 wheels). This is why high buck rides can have $20k/set CF wheels on them - to save 4 to 7lbs over metal.
As TEDS mentioned, it all comes down to contact patch and wheel control (shocks and struts). By just changing those two items can turn a 3rd gen from a ho-hum handler to something that will hang with modern top-notch handling cars.
The real twist comes when you look at wheel and tire selection, 16" OEM wheels are cheap and some versions are light - but there is no tire selection in 245-50-16. 17" will give you a 275-40-17 tire, but some wheels are too heavy and have terrible brake clearance. 18" is going to be expensive as no one makes direct for 18" wheels (yet), but they would be heavier and have less sidewall using a 275-35-18 tire. Testing has shown that the sweet spot is somewhere between 17" and 18" wheels as the negative factors of both smaller and larger sizes are too high to justify.
And most GM OEM 17" wheels are going to be heavy when you factor in spacers - I don't think even the lightest ones will come in less than 23lbs with spacers and won't have optimal brake clearance.
Our cars suffer from:
- the static roll center height is too low, causing too much roll angle
- the dynamic roll center height in dive and roll is too low, causing even more roll angle
- front suspension geometry has a jacking effect and a higher front roll angle vs. rear
- rear roll center was too high
Roll Couple Example: Here are some examples using a 3500# car with 55% front weight to provide some conceptualization:
If the CG is 20” high, and the front roll center is 1” above ground, the car has 55% of the 3500# weight with 19” of leverage to roll the front of the car.
If the CG is 20” high, and the rear roll center is 11” above ground, the car has 45% of the 3500# weight with 9” of leverage to roll the rear of the car.
* Rolling the car that much more in the front overloads the outside front tire & under- utilizes the inside front tire when cornering.
If you lowered the car 2” the CG drops 2”. The front roll center probably moved too, but it’s not linear as it is based on A-arm angles. Let’s say it dropped 1” in the front to 0” above ground and the rear stayed the same at 11”. Now …
If the CG is 18” high, and the front roll center is 0” above ground, the car has 55% of the 3500# weight with 18” of leverage to roll the front of the car.
If the CG is 18” high, and the rear roll center is 11” above ground, the car has 45% of the 3500# weight with 7” of leverage to roll the rear of the car.
* The front now rolls over less & the rear too, making the car run “flatter” - not flat, just less roll angle which works the inside tires better.
So it is very important to know your vehicle, and to minimize the moment arm (leverage) with both front and rear (roll couple) in mind. Getting the front & rear of the car to roll similar is desired. Getting them to roll the same is not, because the goal is: To have optimum grip on all tires and disengage the inside rear tire (to a degree) to turn well, then re-engage the inside rear tire (to a higher degree) for maximum forward bite on exit (Dean would advocate progressive rate rear springs, here). So, on entry & mid-corner, the car needs to roll slightly less in the front to keep both front tires engaged for optimum front end grip (more dive), while allowing the car to roll slightly more in the rear to disengage the inside rear tire, to a small degree, to turn better. For optimal exit, the car will have more roll in the front & less in the rear to re-engage the inside rear tire to a higher degree than it was on entry & exit, for maximum forward bite (traction) on exit.
Going back to the roll couple example, by lowering the car, the front roll center goes to ground level (even below ground under braking-dive). What is needed is to raise the front roll center in order to reduce the moment arm (leverage). Drop spindles are the best method; they can raise 2”, but they are scarce for our cars. Extended ball joints can raise the front RC by 1” - #1. About the rear RC, you can weld-on a bracket to the axle-side panhard bar mount - #2; lowering the attachment point, which lowers the rear RC (small incremental changes, here). In this way, you are decreasing the front roll leverage, and slightly increasing the rear roll leverage so that they are closer together – a better roll couple. These two modifications are the two best changes to make (whether lowered or not), AND they do not cost a whole lot of money. By mitigating the forces applied to the roll couple, you make all your other parts work under less stress/force/leverage. This increases the effectiveness of all the other parts.
By lowering the CG 2”, and using ext. BJ (+1” RC) and PHB mount (-1” RC), the car would have 17” of leverage to roll the front; and, 8” of leverage to roll the rear. These are example numbers, not fact. But that’s a very good outcome for such little money, which also increases the effectiveness of all the other parts.
Lowering the CG helps lessen the moment arm (as in the example). But if we can’t raise the RC out of the weeds, it may be better to raise the car. A bigger sway bar would be necessary to limit the moment arm. Ride height is a tool in the tool kit, not a goal in and of itself.
Now that we have attempted to optimize the roll couple, then we can focus on springs, shocks, and sway bars as tools to control the weight transfer and keep all four contact patches optimal. We tune a car to find the optimum balance of grip. Grip equals speed.
Now the conventional or modern approach needs to be decided upon. High roll/ less pitch (conventional), or low roll/more pitch (modern). Again, these are relative to each other, not extreme positions by themselves. The modern approach puts the nose on the ground (more weight xfer on the front) to provide grip to turn. The conventional approach uses more roll angle to help turn (not that it doesn’t have some pitch). The modern approach can carry more corner speed, but the conventional approach can out-brake going into the corner = two different driving styles.
The conventional will use heavier front springs and lighter sway bar; modern will use softer front spring and bigger sway bar. With a bigger sway bar, you can’t just lock up the front suspension – you need independent wheel movement. Limiting roll helps preserve tire life – better for long road courses. Softer bar with more roll heats up the tires more – better suited for AutoX. But personal driving style/preference will really dictate which to choose. Remember, you have to match the rear with the front choice.
Sorry Brian but a lot of this is wrong and very bad examples. You are even confusing me because I can not continue reading each paragraph know the last was wrong. I will hit some major basic points explaining why.
1) Cars have a front roll center and a rear roll center. Each of these lie somewhere between each set of wheels in both a vertical AND lateral plane.
2) There is an imaginary line that always connects the front and rear roll centers together. This is called the Roll Axis. (No mention of this above)
3)You go right into "Roll Couple example"- What is a "Roll Couple"? You never defined it. You actually did because you labeled it "Movement Arm", but then talked about roll couple for roll axis.
4) Big rear spring, small front spring & big bar is not a think you should be stating to amateurs who are wanting to build a street, autox, or road race car. This "trend as you put it is ONLY a NASCAR circle track thing and it is to put a massive right rear spring on the car in order to rake the chassis down over the LF on a super speedway car (we talking 180+ mph setup turning left to get air out from under and weight the inside wheel to turn while under full throttle on a bank. Ya gotta stop reading circle track write-ups.
5)Back to the Roll Axis and roll centers. Every car with 4 wheels has a front roll center and a rear roll rc (we will label them rc, and the roll axis ra). These rc's are both positioned somewhere between each set of front tires and rear tires. The Roll Axis (ra) is an imaginary line that always connects the front rc and the rear rc even when they move about from suspension geometry and chassis attitude changes. Yes rc's move quite dramatically at times. This roll axis is the only thing the car's chassis will rotate on- best to think of it like a bucking bronco, it is always moving up and down and side to side. You car chassis is like the cowboy sitting on it (Sorry, I was just talking with a good friend in Texas- had to do the cowboy analogy).
In you roll couple examples above, you kind of lead the reader into believing there is two roll points on the car and that the front roll more then the rear does- not true at all.
All I can stop and say real quick before I continue is it is far easier to teach someone roll centers and roll axis from and empty canvas then to try and teach someone that has a misconception of what they do. I do not think my friend you should be writing these articles.
It is IMPORTANT to note when you talk above about spring rates and the amount of weight percentage stuff etc etc that act upon the chassis on the roll couple example thingy is completely wrong. The roll AXIS, (not roll couple), is aways changing angle of attack so to speak. THus, while you are on the brakes, the chassis leverage on the springs is far differently transmitted to the contact patches of all 4 tires then how it does under throttle. You are thinking too much in terms of "static" and not considering dynamic motion.
6) The front suspension jacking effect. This has zero to do with roll centers and roll axis. This has everything to to with weight transfer of the chassis under braking. rc's and ra have zero to do with the adjustment setting. The front suspension jacking effect is basically the angle and leverage (length) of the front strut angles from ball joint to strut mount(yes in essences your caster angle, but more importantly the DYNAMIC suspension angle and the length of the distance the mount is from the ball joint is what the motion on the car goes through when under braking forces of the "front brakes". This can and does rotate weight off the rear tires. Larger rear spring rates will only help lift the rear into the air during this braking period combined with many many many many factors I do not want to confuse people with right now(like Tq arm length, shock damper, canter, swaybar and spring rates and how each react different).
The last thing I will do and I will leave it at that is give a good example of roll centers both static and then maybe dynamic if I have time today. I will use your numbers from above so we stay good in comparison. ***It is important to note you did not account for rc drop when you dropped the chassis 2".
The example you used is a car with the center of gravity that is 20" off the ground. I will take a car that is lets say 27" fender wells arch height as the stock ride height in this example.
At 27" ride height, the front rc is lets say 8" off the ground and the rear rc is 13" off the ground. They have a 101" wheelbase so the angle of the roll axis is 5" lower at the front rc then the rear so draw that imaginary line in your head.
Now you lower the car 2"- what happens to the rc's? They do not drop consistently, no, the front rc drops faster then the rear rc even though the chassis is lowered the same 2".
We now have the rear rc at 12" because the rc is measured at where the panhard rod crosses the center line of the vehicle- thus this only drops half what the chassis drops or equal to a 1" rc drop when the chassis is dropped 2" in the rear. The front however progressively droops quicker and quicker the lower it goes. At 1" chassis lower it went from 8" to 6", at 2" it went from 8" to 3". 3" chassis equals 8" to underground rc like -2"... and so on- it progressively speeds up the amount of drop due to geometry angles of the front a-arms)..
... so now we have the chassis dropped 2" and the rear rc @ 12" and the front rc @ 3". Yes it angles more, NOT LESS like your example. We now have a roll axis at static height that is 9" lower in the front then the rear.... Dynamic motion of this goes worse.
The roll couple (Or Movement arm) is the distance from the cg of the car ( it is ONE "somewhat" fixed point- think sloshing fuel, etc) that acts upon the roll axis. This is based on the weight bias of the vehicle. If the wheelbase is 101" and the weight bias is 60/40= then the cg distance of the cg from the front rc along the ra is about 40.5" behind the front axle (meaning behind the centerline between to two front tires). in the first example the roll couple was about [ 20" cg - about 9.5" ra height at 40.5"= 10.5" roll couple] or leverage movement arm.
The 2" lowered car with now [ 18" cg - aprox 5" ra height along the roll axis 60/40 bias= 13" Roll couple. You can see the lowered car with poor geometry has increase the roll leverage by quite a bit and has cause the chassis to roll on a cantered roll axis as well.
Last edited by SlickTrackGod; 03-13-2017 at 11:42 AM.
Now what most people do not know or understand about a solid rear axle car with panhard rod is that the rear roll center will also yaw (move side to side). Most people do not even understand that the front rc yaws under dynamic motion- so I will point that out also.
How does the front yaw? Because of changing a-arm and strut angle geometry on one side of the car compared to the other in a cornering load, the rc sill move off center. Most cars it is common for the rc to drop and move towards the inside corner wheel.
Now how you do move the rear rc off center? It is done with spring rates. The higher the spring rate on one side of the rear of the car the rc will move towards that wheel a little. In circle track racing for example, we will use lets say a 175 LR spring and a 275 RR spring in order to do this very thing. Why? It yaws (as in Roll, Pitch, and Yaw) the roll axis so the roll axis becomes more of a teeter totter point more perpendicularity the LR and RF tires. Moving the rear rc right it left to right moves it away from the LR tire and makes the chassis more heavy to keep it down. Think of it like a fat kid on one side and a skinny kid on the other of a teeter-totter If the fulcrum is half point the fat kid wins. Move it towards the fat kid and the skinny kid becomes heavier with leverage.
The reason why I bring this up is the mention above of me using progressive rear spring and all this talk about roll centers and front jacking effect/rear jacking affect
Sorry Brian but a lot of this is wrong and very bad examples. You are even confusing me because I can not continue reading each paragraph know the last was wrong. I will hit some major basic points explaining why.
1) Cars have a front roll center and a rear roll center. Each of these lie somewhere between each set of wheels in both a vertical AND lateral plane.
2) There is an imaginary line that always connects the front and rear roll centers together. This is called the Roll Axis. (No mention of this above)
3)You go right into "Roll Couple example"- What is a "Roll Couple"? You never defined it. You actually did because you labeled it "Movement Arm", but then talked about roll couple for roll axis.
4) Big rear spring, small front spring & big bar is not a think you should be stating to amateurs who are wanting to build a street, autox, or road race car. This "trend as you put it is ONLY a NASCAR circle track thing and it is to put a massive right rear spring on the car in order to rake the chassis down over the LF on a super speedway car (we talking 180+ mph setup turning left to get air out from under and weight the inside wheel to turn while under full throttle on a bank. Ya gotta stop reading circle track write-ups.
5)Back to the Roll Axis and roll centers. Every car with 4 wheels has a front roll center and a rear roll rc (we will label them rc, and the roll axis ra). These rc's are both positioned somewhere between each set of front tires and rear tires. The Roll Axis (ra) is an imaginary line that always connects the front rc and the rear rc even when they move about from suspension geometry and chassis attitude changes. Yes rc's move quite dramatically at times. This roll axis is the only thing the car's chassis will rotate on- best to think of it like a bucking bronco, it is always moving up and down and side to side. You car chassis is like the cowboy sitting on it (Sorry, I was just talking with a good friend in Texas- had to do the cowboy analogy).
In you roll couple examples above, you kind of lead the reader into believing there is two roll points on the car and that the front roll more then the rear does- not true at all.
All I can stop and say real quick before I continue is it is far easier to teach someone roll centers and roll axis from and empty canvas then to try and teach someone that has a misconception of what they do. I do not think my friend you should be writing these articles.
It is IMPORTANT to note when you talk above about spring rates and the amount of weight percentage stuff etc etc that act upon the chassis on the roll couple example thingy is completely wrong. The roll AXIS, (not roll couple), is aways changing angle of attack so to speak. THus, while you are on the brakes, the chassis leverage on the springs is far differently transmitted to the contact patches of all 4 tires then how it does under throttle. You are thinking too much in terms of "static" and not considering dynamic motion.
6) The front suspension jacking effect. This has zero to do with roll centers and roll axis. This has everything to to with weight transfer of the chassis under braking. rc's and ra have zero to do with the adjustment setting. The front suspension jacking effect is basically the angle and leverage (length) of the front strut angles from ball joint to strut mount(yes in essences your caster angle, but more importantly the DYNAMIC suspension angle and the length of the distance the mount is from the ball joint is what the motion on the car goes through when under braking forces of the "front brakes". This can and does rotate weight off the rear tires. Larger rear spring rates will only help lift the rear into the air during this braking period combined with many many many many factors I do not want to confuse people with right now(like Tq arm length, shock damper, canter, swaybar and spring rates and how each react different).
The last thing I will do and I will leave it at that is give a good example of roll centers both static and then maybe dynamic if I have time today. I will use your numbers from above so we stay good in comparison. ***It is important to note you did not account for rc drop when you dropped the chassis 2".
The example you used is a car with the center of gravity that is 20" off the ground. I will take a car that is lets say 27" fender wells arch height as the stock ride height in this example.
At 27" ride height, the front rc is lets say 8" off the ground and the rear rc is 13" off the ground. They have a 101" wheelbase so the angle of the roll axis is 5" lower at the front rc then the rear so draw that imaginary line in your head.
Now you lower the car 2"- what happens to the rc's? They do not drop consistently, no, the front rc drops faster then the rear rc even though the chassis is lowered the same 2".
We now have the rear rc at 12" because the rc is measured at where the panhard rod crosses the center line of the vehicle- thus this only drops half what the chassis drops or equal to a 1" rc drop when the chassis is dropped 2" in the rear. The front however progressively droops quicker and quicker the lower it goes. At 1" chassis lower it went from 8" to 6", at 2" it went from 8" to 3". 3" chassis equals 8" to underground rc like -2"... and so on- it progressively speeds up the amount of drop due to geometry angles of the front a-arms)..
... so now we have the chassis dropped 2" and the rear rc @ 12" and the front rc @ 3". Yes it angles more, NOT LESS like your example. We now have a roll axis at static height that is 9" lower in the front then the rear.... Dynamic motion of this goes worse.
The roll couple (Or Movement arm) is the distance from the cg of the car ( it is ONE "somewhat" fixed point- think sloshing fuel, etc) that acts upon the roll axis. This is based on the weight bias of the vehicle. If the wheelbase is 101" and the weight bias is 60/40= then the cg distance of the cg from the front rc along the ra is about 40.5" behind the front axle (meaning behind the centerline between to two front tires). in the first example the roll couple was about [ 20" cg - about 9.5" ra height at 40.5"= 10.5" roll couple] or leverage movement arm.
The 2" lowered car with now [ 18" cg - aprox 5" ra height along the roll axis 60/40 bias= 13" Roll couple. You can see the lowered car with poor geometry has increase the roll leverage by quite a bit and has cause the chassis to roll on a cantered roll axis as well.
This was meant as a summary or primer in order to state my belief that optimizing the fr RC and rear RC are the best first step to take; therefore, I did not mention dynamic changes very much (passing reference to "dive"). It was not meant to be all inclusive in the original posts, but I did hope that further discussions would go in that direction - so your points are well taken and they fill out the discussion.
1) Yes
2) Yes, no mention of entire vehicle roll axis as my point was to optimize fr and rear
4) No, I don't think so - not a NASCAR guy
3) & 5) Here's where we do have some disagreement. I do believe the front can roll more or less than the rear. I think you may have a point in the way I am using 'roll couple'. The way I use it and the accepted definition may be conflicting. The way I used it was a term to describe both fr and rear RC's along with my belief that they have different roll rates - and you say only the one roll axis. The front and rear suspensions is what I am referring to, as of course the vehicle is one. There is more weight up front, larger moment arm, and larger spring/sway bar than the rear. So maybe I should have gone into Front Lateral Load Distribution vs Rear Lateral Load Distribution, but I didn't want to write a book.
6) Agree, I just mentioned it and that RC does contribute - never mentioned anything else.
I did briefly account for the RC drop when the CG dropped - not linear and it does depend on a-arm angles in the front.
How do you define cantered roll axis?
It's hard to summarize a difficult subject without leaving things unsaid. If I've badly misused terms, let me know, and I will correct. I do need to use the same definitions. If I haven't communicated well, that's ongoing in life (mine, anyway).
I'm more committed to the truth, than my own beliefs about the truth!
It is not about misuse of terms, its to the point you do not fully understand what you are trying to teach. Sorry , not trying to come across harsh but I keep to facts, its nothing about friendships.
Case in point- you say 3 & 5 is where we disagree. There is not opinion here, you are wrong. The car rolls on the roll axis... period. The positions of the front and rear roll centers are what define the roll axis at all times in all moving conditions. Things are moving around and thus the roll axis moves. The car has a cg and this acts upon the roll axis. Stop thinking in terms of the chassis moving about the rc's. Th cg and rc have no relation. The cg has relation to the roll axis.
Push a pencil through a kleenex box and spin the box via rotating the ends of the pencil. That is the roll axis. Take it out and restab it into another position, roll it again, and again. The roll axis is just that.
Define canters roll axis? I defined roll axis. Cantered as we all know is slang for such like a "cantered vehicle" or a vehicle that is tilted funny. Thus cantered roll axis. It will tilt the chassis funny if it is tilted funny.
I happen to eat sleep and breathe this stuff and have been teaching it for a few decades- with that said I was confused reading this post.
edit to add (humor) Canter is easier slang to write then cattywhompus, or jerryrigged
Last edited by SlickTrackGod; 03-13-2017 at 01:30 PM.
I am trying to find how the word canter is to be used properly. I could not find anything on "canter" other than horses- even though I've heard and used the slang my entire life. I see it defined as cant. If you say something "cants" then it leans or tilts. I just somehow seemed to develop the use of the word canter by mistake. If I purely write "cant", it does not seem to mean the same to me as saying "Canter" or "Canting affect". I usually say it's all cattywhompus (or, It's all f*cked up)
What I refer to as canter has to do with both pitch and yaw. Maybe there is no term to define this and I invented one.
****cant2
kant/Submit
verb
verb: cant; 3rd person present: cants; past tense: canted; past participle: canted; gerund or present participle: canting
1.
cause (something) to be in a slanting or oblique position; tilt.
"he canted his head to look at the screen"
synonyms: tilt, lean, slant, slope, incline; More
take or have a slanting position.
"mismatched slate roofs canted at all angles"
Th cg and rc have no relation. The cg has relation to the roll axis.
I'd rather have the truth, than an inflated ego. No problems, here.
I don't believe the first sentence, and agree with the second. The moment arm is the difference between CG and RC. How can they not be related? Is the moment arm meaningless? Perplexed, here.
I still believe that the goal is to have the front and rear roll similarly, but not the same.
Gotta go, Making a BDay dinner for my Dad who is 87 today. Check back in tonight.
I'd rather have the truth, than an inflated ego. No problems, here.
I don't believe the first sentence, and agree with the second. The moment arm is the difference between CG and RC. How can they not be related? Is the moment arm meaningless? Perplexed, here.
I still believe that the goal is to have the front and rear roll similarly, but not the same.
Gotta go, Making a BDay dinner for my Dad who is 87 today. Check back in tonight.
You have to put the movement arm on the roll axis not to a roll center. Where along the roll axis is based on the individual car's weight bias. The only way a movement arm would act almost entirely on the front rc is if the car had 99/1 bias
The reason I use rear progressive springs is because when I press the car into a corner the rear RC moves outward yawing the roll axis and leveraging weight onto the inside wheels. This is an act and react process that builds and releases as the forces build and release. You have to look at this technique as somewhat of a spring load onto the roll axis. It is quite hard for people to grasp this. There is no program or model that can or would be able to display this force. Somethings you just have to understand in 3 dimensional imagination.
Best I can explain it is it really does not happen because as it does it has an immediate counter force that cancels it. The more it loads, the more it weights to keep it where it should be.
I still believe that the goal is to have the front and rear roll similarly, but not the same.
If you really think about what you are saying- the chassis would have to twist/flex and then bend back each time that happened. Just food for thought
I know this stuff makes peoples heads hurt. The main problem is thinking too much about this on paper. Just go and adjust them on the car until it feel right and give your brain a rest. Needing extreme advanced knowledge of this is only really needed when trying to build a car from scratch.
Had some great ribeyes last night. Dad was recalling his years at Snap-On in the 50's. He had two Desoto Sportman's with Hemi's (55 & 56); then, marriage & kids stopped that. I guess I should thank him!
Dean, of course, there is one body and it doesn't flex (well, hopefully uni-bodies don't). I disagree that there is no relation to RC and CG. I do know that the distance between RC and CG determines Force (moment arm) - that is a relation. I also agree that one should not teach errors.
Force acts upon the CG thru the moment arm (attached to CG and roll axis, roll couple, whatever term). I think we are on agreement, here.
My main point still holds: optimize the distance between both fr and rear RC's to CG. It's the best bang for the buck and increases the effectiveness of all other suspension parts. By bring the front and rear roll angle (maybe this is the better term) more equally, you have a much better handling car. It is always better to improve geometry, rather than trying to compensate for geometry by harsher bars and springs.
I tried to keep it short, and it is still too long. I never intended to address everything and never mentioned moving the rear RC off center. It's not central to my point.
The ext BJ and PHB bracket are easy geometry mods. It is not beyond the grasp of newbies. If I had gone into front a-arm/spindle geometry changes or ackerman, that would have. This is an easy fix, and has what I believe to have the greatest single benefit - reduction of force by geometry (1) rather than correcting of force by parts 2 - (big bars/big springs, etc.). That is why I listed this as 1, bars and springs 2, and unsprung weight 3. Of course, one can debate this.
I like the discussion and have learned a lot from you; and will continue to, friend. I just hope that the deeper discussions don't scare away the newbies from attempting such a great modification. It is within their grasp.
When I used Roll Couple, I used an old school description - see old school pic. OK, I'll get around to changing the term to roll angle (fr & rr) - see the other pics. I'll also add another term - roll moment. Many people use different terms plus add the difficulties of internet communication and its difficult.
Yes, the car rotates on the roll axis (lets decide on that term). Angle your pencil through a loaf of bread - bottom front to upper back of loaf. Pull the pencil out and slice the loaf. We can discuss the roll centers position (hole left in slice) in the different slices. The roll angle of each crust can be discussed as in the pics below. I get that you always want to talk about the whole loaf, but you can discuss the slices and their relationship to one another, too. Yet, you are correct in reminding us that it is still the whole loaf that counts.
All four of those drawings have something wrong with them. 1 &4 have some good points, but bad reference points also. None of the 4 are correct. Keep in mind that just because its in a book does not mean it is correct. These are primitive drawings from people who thought they know and if you are following that I can see why you think what you do.
Lets back way up and toss everything out the window. Lets start by you hearing for the first time the term "Roll Centers' Keep in mind there needs to be TWO of them. This is very important now----->>>> CENTER....meaning pivot center of ONE END OF A LINE. You need to ALSO INCLUDE the OTHER END OF THE LINE.... Hence Roll center"S".
These are nothing more then reference positions that the roll line travels through. THEY ARE NOT, I Repeat, THEY ARE NOT the points where cg is applied over and around like they are a ball joint. They are NOT. The cg has reference to the ROLL AXIS....PERIOD!!!!
I can not stress the above information enough. Keep reading it over and over until you get all those other thoughts out of your head... the other thoughts are WRONG.
Where along the roll axis the CG is applied is based on weight bias of the car. It will be the center of gravity which will act upon the roll axis at that balance point long the span of the roll axis at some point WAY IN BETWEEN the two Roll Centers at the ends that define the roll axis.
..... I disagree that there is no relation to RC and CG. I do know that the distance between RC and CG determines Force (moment arm) - that is a relation.
I will detail very plain and simple why this is wrong.
How many cg's do you have in a car?......One, Not two, one. You know where I am going with this?
If the cg had relation directly to each roll center then how would it apply all the car's center of gravity over the front rc, and then at the same time apply all of the car's center of gravity over the rear rc? It can not physically happen. The cg is applied to the roll axis. This lever arm...movement arm... roll coupler (all three the same reference terms) from the cg to the ra is one cg that is applied to one roll axis.
Force acts upon the CG thru the moment arm (attached to CG and roll axis, roll couple, whatever term).
Force acts upon CG thru moment arm to the roll axis. We are saying the same thing.
Dean, I do not understand why you are making an argument where one doesn't exist. It's just like the line you edited out where you were trying to describe something that doesn't exist.
Lets start by you hearing for the first time the term "Roll Centers' Keep in mind there needs to be TWO of them. This is very important now----->>>> CENTER....meaning pivot center of ONE END OF A LINE. You need to ALSO INCLUDE the OTHER END OF THE LINE.... Hence Roll center"S".
Dean, you can't teach me what I already know and stated. Maybe you need to start reading for the first time.
Originally Posted by TEDSgrad
TERMS: Roll Center (RC): Cars have two roll centers - front suspension & the rear suspension. They act as pivot points. When a car experiences body rolls during cornering, everything above that pivot point rotates towards the outside of the corner, and everything below the pivot point rotates the opposite direction, towards the inside of the corner.
Are you that butt hurt? You are saying some things correct, and some things wrong. I am adressing what you said wrong by specifically quoting your statements. You then come off like a ****ing child and talk some bullshit nonsense about me editing something?
I was asked by someone that saw this and was confused to come in here and read this post. I did so and corrected misinfo. You want to come off all high and mighty Ill just delete my posts and be gone.
Edit to add: I see you put your tail between your legs and left. You were online enough for me to see you read this. Brian, your posts are wrong. Saying some things correct and some things wrong still makes a bad post. You;ve done nothing to correct it. You continue to argue that CG has relation to an individual rc, and I am probably the only one on these boards knowledgeable to see you do not understand what you are trying to write by developing this thread. I have directly quoted your misleading statements and have done an adequate job in explaining why they are wrong, you come back and put up quotes by yourself as to why we agree and overlook what you posted wrong several times now. You can't be half right and think you can teach others misleading stuff without being challenged on it. I see bad info and I will correct it. Don;t like a debate on facts? get out of the kitchen partner. Otherwise ****ing quote what I said wrong and explain why I am wrong.
Last edited by SlickTrackGod; 03-15-2017 at 12:06 AM.
Why don;t I make you look like a ***. Explain to me the movement arm length a 4000 lb car with 100inch wheelbase, a front rc of 4" and a rear RC of 10" and the cg 12 feet in front of the front tires at 72" off the ground?
Why don;t I make you look like a ***. Explain to me the movement arm length a 4000 lb car with 100inch wheelbase, a front rc of 4" and a rear RC of 10" and the cg 12 feet in front of the front tires at 72" off the ground?
That is a very poorly designed car. The one positive is all of the money you would save on rear tires & brakes and the optional rear wheels.
That is a very poorly designed car. The one positive is all of the money you would save on rear tires & brakes and the optional rear wheels.
Yes, well can you tell me what it teaches about weight distribution on the roll axis? There is a major point about this I am seeing if anyone will catch onto and can answer.
Dean and Brian,
I admit that I do not know as much as I should about suspension. Along with making the car handle on the road course so that I am comfortable and confident with it. I enjoy reading all of the topics on handling and have learned enough to realize that I have much more to learn.
I have found that the post from both of you have helped me the most. However I am still a babe in the woods for wrapping my 58 year old mind around some of the concepts. It is helpful to see drawings and SIMPLE explanations to concepts that sound simple (roll center movement arm to give a couple) the center of gravity I understand but I am suffering a mental block on some of the other concepts.
So please can you both take a deep breath and slow down a bit and perhaps tackle one concept at a time? For example lets say front roll center. How is it measured? what effects it? how do you adjust it? then move to front movement arm, rear roll center, rear movement arm ect... Perhaps it's not possible to break this up into small bits like that but if it can be my pea brain would not hurt so much LOL
Dave
Ill answer it with this drawing. Albeit a very unstable application when not loaded with a rear trailer, the physics of the tractor pictured above would have a movement arm outside of the roll centers if not loaded with a trailer. This is merely a representation showing that the movement arm can connect along the roll axis anywhere based on changing cg
The major point? Any roll axis does not stop at the RC's- it goes through them. THey are nothing more then fulcrum points for the roll basis and are not the pinpoints of roll. There is NO RELATION.
The major point? Any roll axis does not stop at the RC's- it goes through them. THey are nothing more then fulcrum points for the roll basis and are not the pinpoints of roll. There is NO RELATION.
You cannot have the roll axis defined without knowing the RC's - they are in relation. god (high & mighty) keeps saying they have no relation, and no one can argue with god, or he resorts to name calling (childishness). Then he accuses me of what he is guilty of. The word for that is hypocrisy.
I have also repeatedly said that Force acts on CG thru moment arm on the roll axis. Force does not act on the RC as a single point, but the point is part of the entire axis (it has relation). To say otherwise is to assert that the roll axis is independent of the RC, but he has just stated above that the roll axis does go through the two RC's.
I think I just need to print this off to go over is in black and white Brian and Dean do either or both of you have some suggestions on what other books, web sites or posts that are good for beginner's? Sort of a walk before you run kinda thing with me!!! My issue that I hope to work on this year is corner exit I am 100% happy getting into the corner but could use some help from middle to exit. Well I think this thread should remain a generic one for everyone to benefit from I am hoping to find some resources to help my car Thank You both as this is the best thing of this site is the sharing of ideas and the chance to save making the mistakes someone else has made.
Dave
I'll let others suggest the books to you.
I like Brent Vandervort, Ron Sutton (over on Pro Touring forum, stickies in the suspension sub-forum), and Dean (despite our differences and his personal attacks, I've learned a lot from him, have a suspension build thread titled, Following Vetruck).
I'll attempt a more simpler explanation (which leaves out stuff).
Force is applied on CG which transfers that thru the moment arm onto the roll axis - the vehicle then rolls. The CG, moment arm, roll axis, and RC are related to each other - see pic.
The RC's are two points on the entire roll axis. They are the important points, but we must be careful and say that the entire roll axis is involved. Though we talk of RC points, the are not separate from/independent from the Force being applied to the entire axis simultaneously. But as points on the roll axis, we can say that Force is applied to those points - just not separate from the whole. We can slice out the two RC points and talk about them conceptually, but remember they are part of the whole.
My examples in post #2 of changing the leverage arm (moment arm) changes the leverage (force being transferred) from CG to the roll axis. These geometry changes change the Force being applied. The amount of Force remains the same, we are changing the portioning to to achieve better contact patch on the four wheels - that is the goal of all of this. Pitch and dynamic changes will effect this too, but I'll leave that out for simplicity sake but don't forget them. By raising the front RC point along the roll axis, we shorten the moment arm (leverage) and decrease Force applied. Think of the moment arm as the hypotenuse of a triangle with the CG and roll axis as the right angle. Lowering the rear RC point on the roll axis lengthens the moment arm (leverage) and increase Force applied. Remember the weight distribution is not equal front to back. We are changing the multiplier - the leverage factor for the purpose of better 4 wheel grip. Though I speak of front and it's moment arm, and rear and it's moment arm in relation to RC points; there is only one moment arm - one CG to one roll axis. CG and moment arm is moving around due to dynamic movement or weight transfer. We are trying to manage the weight transfer by altering geometry points to achieve the best contact patch.
The whole premise of this thread is: it is better to start with altering the geometry points first (costs less, bigger bang, a newbie can do the two mods w/out complete theoretical understanding), then use springs and bars to control Force (experimentation and personal preference is involved), then finally unsprung weight. By changing these RC points, we are changing the roll axis. That's why they have to be related. They are points on the roll axis, but not separate from. We can speak of them separately, change them, and speak of moment arm to RC point in concept; but they are part of, and changes will alter, the roll axis as a whole.
They must have relation, or the roll axis cannot be changed by altering the RC's. Only one can be true. A change in the one affects the other; OR NOT.
Go ahead and now change the focus more with bullshit.
This is not helpful, and does not diminish me.
I can pull points out of the axis and speak of them separately. Speak of the CG, the RC points, and the resulting moment arm - front and rear. You interpreted that I was implying multiple moment arms in real time, when I was talking about the moment arms (front and rear) in relation to changing the RC points.
You read too much into what I left unsaid/or was unclear, then starting attacking me. Why? I readily admit that you know more than I do.
High & Mighty? - I am currently not working and living with my parents. My father is 87 and has had two Bi-PE's (blood clots in both lungs simultaneously) in two years; and my mother has had Parkinson's for the last 25 years. They can no longer do the things they used to. I am putting my life on hold (helping them stay in their home) while I honor my father and mother. Their value is not in their superior knowledge or what they can do. Their value is in being my parents. We are human beings not human doings.
In the same way, not every ThirdGen is a high dollar/high performing car. But each one has value because they are ThirdGens.
Dean, you have great knowledge and skill. Please don't use it to club people down while you are exalted (god). Intellect, talent, and skills are given at birth. You could just as easily been born a female in Ethiopia with none of those. Or, you could be born with all those, yet in Aleppo or Mosul with no opportunity to develop them. Please live by gift; appreciate, be gracious, be grateful, be thankful for the gifts given unto you, be humble (but not a doormat). You could build the 'ultimate suspension,' but drive it down the road to perdition - what does that profit?
All this talk of performance is great. But once you start attacking persons and their being, you have gone off track nor are you a god. Please correct your course and get back on track by being mindful of all that you have been given. Then you can show more patience to those of us who have less than you.
You both are right, but for different reasons. From a technical/mathematical standpoint (Dean's point of view) Cg and roll centers are NOT related; meaning if you change one, you do not in any way, affect the other.
HOWEVER, when talking about how roll axes and Cgs affect a car's dynamic movement from external forces (Ted's point of view) they ARE related, though indirectly. I.E. In order to know how much a car will roll, pitch, yaw, in a turn you need to know both the Cg and roll axes, among other things.
Now we're going to label it as an indirect relation? You guys are just confusing everyone. Of course thete is an indirect relation. There is no direct relation of weight movement from the cg to the rc through a movement arm....period. Dont confuse tbe matter, this is about applied levetage of the chassis weight to tje roll axis. They fix the axis location or the roll, but they in no way have weight directed from each rc point. You have to look at the cg to ra relation as a gyroscpe sort of speak. Amy relation of weight from the cg to a rc point would mean the the rc is a fixed pivot. It is not so the is no relation of weight distroburion betwwen the cg and each rc point. The relarion you both are seeking is a relation of geometry, not a relation of weight movement.
I can pull points out of the axis and speak of them separately. Speak of the CG, the RC points, and the resulting moment arm - front and rear. You interpreted that I was implying multiple moment arms in real time, when I was talking about the moment arms (front and rear) in relation to changing the RC
Brian
For the last time, there is no front and rear movement arms. The book and diagrams you ate reading and quoting from are poor explinations and are misleading you. You keep repeating this and i explained why it is not so. The car chassis would twist and flex/compress for this to be true. You just are not getting it. One cg and one roll axis. Tjat is the simplicity of body roll movement and weight distribution.
I don't believe the first sentence, and agree with the second. The moment arm is the difference between CG and RC. How can they not be related? Is the moment arm meaningless? Perplexed, here
I think what SlickTrackGod would say if he was in a better mood is that,
* Center of gravity is related to mass. It is a concept invented for the purpose of being able to do analytical analysis.
* Roll Center is related to motion. It is constrained by the geometry of the suspension members and the ways in that those member allows movement.
The two are different concepts, different units, and independent..... ergo not related. There are other concepts that are expressed as a function of CG and RC.
I think what SlickTrackGod would say if he was in a better mood is that,
* Center of gravity is related to mass. It is a concept invented for the purpose of being able to do analytical analysis.
* Roll Center is related to motion. It is constrained by the geometry of the suspension members and the ways in that those member allows movement.
The two are different concepts, different units, and independent..... ergo not related. There are other concepts that are expressed as a function of CG and RC.
What makes you think I am angry or in a bad mood? I have repeatedly tried to say to him what he is saying is wrong and emphasized the points with bold letters so they will stand out, where is that a bad attitude> I have also put specific quotes of his that are wrong, then he comes back with quoting some of his quotes that are right. I do not have a problem with that other than he is dodging and not understanding the focus on him stating several different times and ways that the front RC has a movement arm to the cg as well as the rear rc has a movement arm to the cg- they DO NOT. He is looking at these drawings he keeps posting as references and thinks there is cg over the front axle and there is also cg over the rear axle. There is NOT. A movement arm from a rc to a cg is much much longer and would be massively increased leverage over the actual movement arm (this is also call roll couple) because the angle to get it towards the car's cg would make it aprox 1.5-2 times the length. You do not draw a movement leverage roll couple arm from a rc to the cg...period. Get it? I have repeated this how many times now? Calmly, not anger like some of you presume in my typing? Read my stuff in a clam voice- I type factual with no emotion other then to emphasize a point by capitalizing it.
Now where I said Brian is butt hurt? It was right after he dodged my quote of him and explained it was wrong he then quotes a different quote of himself where I have no issue with- then tells me to read. So ya, there I basically I gave him attitude right back. Stay on topic. The topic is his persistence to say the RC to cg are movement arms. They have zero relation in the weight transfer. My next post I will show why with drawings.
Here is a comparative example of two cars with the same gross weight of 3000lb. Both are same ride height, both have same suspension geometry, both have same spring rates, shock rates, and sway bar sizes. Both have identical roll centers at static ride height and thus the have identical roll axis'. THe difference is weight bias. One car is 50/50 with weight redistributed to the back of the car etc (what ever was done to do this does not matter, on scales if weights 50% front and 50% rear on each axle). The second car has a lighter rear end and a heavier engine- but again both are identical overall weight etc.
If yout ake the photos that Brian posted and go off of using leverage arms up to the yellow line which is the height of the cg on both cars, you would have no difference between the front roll couple and the rear roll couple- each car would handle identical.....Yet, THEY DO NOT.
Now when we look at the cg positioning and place it where it is scaled at(fore and aft in balance (note the purple dots along the yellow cg height line)- you now look at the one and only roll couple from the cg to the roll axis. Note the 70/30 car has a longer roll couple (distance between the cg and RA) then the car with 50/50. With the same weights and same spring rates & sway bars, the 70/30 car will have more overall roll angle into the same corner (ie- the car will lean more then the 50/50 car with the shorter movement leverage arm.)
Dean,
I never said that there are two moment arms. I talked about them conceptually to help people understand. I have stated there is only one. The pics are only aids.
Let's use yours above. Let's use the 70/30 and say static only for now. The purple square is CG. The purple line down from it to the light blue roll axis line is the moment arm. We have three points: CG, RC, and point where MA is on the RA. If you raise the front RC (which is single point on the RA) to the top of the wheel, the moment arm is shortened which means leverage is reduced. If we lower the rear RC to the bottom of the wheel, the moment arm is lengthened and leverage is increased. This is meant to show the shortening/lengthening of the moment arm and is exaggerated to see/conceptualize the effect. What I was actually trying to say, was that it is best to raise the front RC up to just below the center of the front wheel; and, to lower the rear RC to just below the center of the rear wheel- so that they would be similar, but not quite equal, but that's not much change to conceptualize.
I never wanted to go into dynamic movement - wanted to keep it short. I never tried to say everything. Plus, the RA is not a straight line, but rather jagged. Again, it is easier to conceptualize.
I have already apologized for not being clear, and for misusing a term(s). Of course I have become defensive after all the "you don't understand anything" accusations, and where I had to quote myself to you to refute you. Then, we've been talking past each other. I haven't changed anything to save face. Any edits are in a minute or two of posting - you can look at time stamps if you want.
I can admit my guilt - I am in the repentance & forgiveness business, after all.
The changing of the RC's does altar the distance of the roll axis to CG. There is relation of the RC's to the RA. I never meant to describe or go into detail.
You do not draw a movement leverage roll couple arm from a rc to the cg...period. Get it?
Yes, I understand and agree.
I also believe that in practice TEDSgrad agrees too. He's even said so. He's just a little convoluted in how he explains it and you're behaving like a pitbull and won't let go of the topic.
Originally Posted by SlickTrackGod
What makes you think I am angry or in a bad mood?
You get wound up when people won't submit to you.
I know where the frustration comes from.... I think this topic matter happens to be your professional specialty, right? You just have to realize that on the internet you lose the respect of your "position of office". All you can do here is lay out information and let people take it or leave it. Anything beyond that is not very fruitful because you're not dealing with your peers, you're dealing with the general public. I am not encouraging you to go silent but you have to know when further efforts no longer brings value, my friend.
If the debate were a bit more civil, if would definitely make for more enjoyable reading. But, it is what it is, and I'm hanging on every word typed by each of the primary posters, points and counter-points. After you distill it all down to it's essence, there is real gold to be extracted from this conversation.
I think what SlickTrackGod would say if he was in a better mood is that,
* Center of gravity is related to mass. It is a concept invented for the purpose of being able to do analytical analysis.
* Roll Center is related to motion. It is constrained by the geometry of the suspension members and the ways in that those member allows movement.
The two are different concepts, different units, and independent..... ergo not related. There are other concepts that are expressed as a function of CG and RC.
Thanks for saying what I was trying to say, but much better.
Guys,
This reads much worse than it is. Dean and I have no animosity towards each other. We are just debating in public where everyone get to see.
Most of the time, a perceived slight or insult, I will just let go on by. I try to be meek and humble (not weak and a doormat). I will push back out of self defense, but also to hopefully try to correct what I perceive to be not helpful behavior. I like Dean, and want him to improve how he comes off on-line. He has helped many people, and he does not need me to defend him. He is very likeable and personable on the phone. Somehow, on-line he comes off very different.
With the exception of foul language (my standards are high) and a couple personal attacks, I am enjoying this.
I agree Ted. I have no anger and do not understand wete people perceive that. I reread this entire thread and dont get the impression that was said of me. Did i beat a dead horse? Hell yes- i feel it was needed and pointed out why as the thread developed. I understand this stuff and i guess i see and read things that others do not understand will lead people to believe false info. Ted means well by all means. I was correcting his diagrams and text because i see how it is misconstrued.
If i didnt beat a dead horse here, this thread would not have transpired more clear summuries on the roll axis and how it is weighted. I challange antone to find clear illustrations in any book anywhere that detail my last illustration above. Why? My experience rememberong way back when i learned this reminds me how confused i was at times about this stuff. I have come to realize i know more about this stiff then ant book ive seen. Arrogant statement? Maybe, but that is how some will take it while i write it as fact off of my knowlexge level and hands on ecperience in life. Most of this you can not teach in text. I could show people things in person 100x easier then trying to explain on these forums. Ted is a friend. Sometimes friends disagreebut that does not make is enemies. As for language? I ****ing talk that way
Edit to add: we all also lnow my typing ability sucks. It is even worse right now typing this response on my little phone with big fingers. Im a robotiic two index finger pecker at a keyboard. I dont get the internet emotion crap. I just type robotic.
Last edited by SlickTrackGod; 03-16-2017 at 04:09 PM.
03-11-2017, 10:59 AM
