InfernalVortex

iTrader: (4)

I've decided this is a worthwhile endeavor, but Im trying to pick out front springs.

Does anyone have any idea what size springs I should be using to get a nice range of adjustment from slammed to stock height for the front springs? I'm planning on going with 700 lb springs, but I may go with 800. But that's my target at the moment.

IROC springs are allegedly at 10.75" load height. Im not sure how they came up with that number. I do know that my weight jacks will take up about 1-1.5 inches of spring pocket area. So adjusted all the way (with the spring cup against the frame plate) my springs need to be 9.25" at load height to be at stock height, and that leaves me NO room to lower the car at all. So I need something that's probably in the 7-8" load height range.

I'm seeing springs in 5.5x8, 5.5x8.5, and 5.5x9.5 . Does anyone more familiar with this stuff than I have a suggestion for which size would work out best? Should I just go with the smallest and use the jack itself or is there a tradeoff for going with a shorter spring? Or at least know the measurements where our spring is on the A-arm so I can work out the formula for how much weight each spring sees?

Does anyone know how tall the ground control springs are (unloaded) as Im basically copying their design.

TEDSgrad

iTrader: (4)

I can't help you with that design. I'm running 9.5" #850 springs with the swivel cup design. When I spin the bolt to the top, I can pull the spring out with fingertips. I've also got the drop spindles, too. Taller spring gives a better ride - I have considered a taller one, but I definitely would have to use a spring compressor for that.
What springs do you have in the rear? I would go at least #850-#950 with your block.

Read through this: https://www.thirdgen.org/forums/susp...ol-weight.html

InfernalVortex

iTrader: (4)

That is an excellent thread! Thank you!

Im wondering if I should go with swivel seats... Doesnt really seem necessary, though. The seats I was planning on using allegedly allow some range of movment.

InfernalVortex

iTrader: (4)

So now after reading that I've made some alarming discoveries. These are the ride heights of my car at each corner according to the fenders.

Now my garage may be slightly uneven... but it's always sat a little high at the passenger rear, I just attributed it to various whatevers in the spring rate variances...

But now Im thinking that this arrangement is literally impossible without the frame being bent. There's no way for the lowest fender height and the highest fender height to be on the same side of the car unless it's twisted up somehow. Am I wrong?

Now Im wondering if I should even continue with this car any further.

Alice89

iTrader: (6)

If your reading from fender lip heights it may just be a slightly tweaked body panel. It could even be a blown gas charged shock on one corner. Springs may have shortened. Possibilities are endless.

Even if the chassis is tweaked it's not the end of your car. It's fixable.

Also as you mentioned your garage floor may not be level.

InfernalVortex

iTrader: (4)

Well, its not that it's sitting uneven, it's that the lowest and highest spot arent opposite of each other, they should be on opposite corners of the car. Either way, I decided to find a different patch of concrete to do it on... and the measurements came out like this:

26.75---Front---26.63
27.75---Rear----27.75

So in a different spot, it's only a 1/8" inch difference. That's a lot more reasonable, and tolerable.

Im thinking of the car as a steel plate sitting on the ground. If it's a uniform thickness, then all four corners should be the same height. If one corner is higher, then the opposite corner will be lower, and the two "middle corners" will be in between. But I guess it just depends. It might be that my garage isnt level ,that I cant drive "straight" into the garage spot (it's an L turn to get into my slot from the driveway), or that the tires are turned when I stop rolling the car forward... I dont know. I guess it could be a lot of things. But lesson learned, measuring fender heights is a highly variable process and needs some very strict constants and measurements and controls to eliminate variables. Which Dean mentioned in the thread that was linked in the thread that TEDSgrad linked... Good information there... but just goes to show that there's always room for error if you're inexperienced.

SlickTrackGod

If you have to turn the car to get into the spot then just back out stright as far as you can at that point and reneter the spot with the wheels straight and the chassis relaxed. Something as simple as how hard you hit the brakes / or just roll to a stop will differ the chassis height, as well as if you are in it then stop and get out, or you roll it back and forth without you in it (best means). Ground is never fully accurate- very rare- almost all concrete slabs have pitch for some kind of drainage or slight elevation change.

I am fighting this right now setting up our current race car on a very uneven concrete driveway area. My rake in the chassis is off by 1/4" from there compared to the tech bay at the racetrack. It was a new area/team/vehicle/etc for me this year and I am learning the area I am having to work with and how it varies in capatability to the flat tech bay. in other words, if I have the car flat in the tech bay with the left front @ 4 1/4" ride height, I then gauge it in my work area and see the same car has a 3 15/16" height in that corner on the ground I am working upon. In my case, I leveled the tire patches, but I take my measurements under specific chassis points because I have no fender lips when the fiberglass body panels are removed.

Even with the knowledge I have, I am struggling right now with very time consuming methods of setting this racecar. It is a used racecar my team owner bought with limited funds and has actuall sold the scales last month on me to buy tires for the first race after I used them here to setup the truck for the first time. I used the spring rates already on the truck and made educated guesses on a setup. The first race was a disaster because our brand new spec crate motor somehow ended up with an "Alcohol" carburator on a gas motor from our engine guy- that (insert four letter word) us. IWe had no speed and thus fought all day trying to even get up to race speeds- were lapped almost 4 times int he race- no sufficiant chassis data. Then next race 2- I had the truck out there 4 times total collecting data- second run my pyrometer took a crap- there goes data and the need for another $500 new pyro-ouch) Finally getting speed, I made tweaks to the chassis and improved lap times all 4 times on the track, but we were still lapped twice by the leaders- very frustrating from my standpoint on the sidelines. I can see Ron is giving up alot going into te corners and having way too much chassis travel and change of footprints undr hard braking and the truck will not turn- so he has to brake early and slower and gives up a car length entering both turns 1 & 3. My point? I know have to try and rip apart the complete frontend and go from the 200 lb springs to a 325 lb spring setup (I am much more familiar with thank goodness) but have to do so on uneven ground I am not real familiar with and WITHOUT scales. Race 3 is going to be a chaotic day. I am praying for an open practice night prior to that race so I can get this thing dialed in the old fashion way of trial and error snce I have no baseline crossweight data without scales. I have so many things to hunt I will need about 20- 6 lap sessions to get it dialed. With scales and a flat work surface I need about 10.

InfernalVortex

iTrader: (4)

Thanks for the input, it definitely makes sense. I measured at a different spot on the driveway today and it was dead nuts even side to side. Doesn't mean the car is straight, but it does mean there are a lot of different aspects to it. I would imagine fender lips are probably the worst way to measure, right? And when you say "leveled the tire patches", do you literally mean you add some sort of shim under the tires to get all the tires to the exact same height?

Just curious, have you ever read anything by Steve Matchett? He was a Formula 1 mechanic with Benetton (Schumacher era, Ross Brawn) in the early 90's... hes one of the guys in this picture:



I've read Life in the Fast Lane and A Mechanic's Tale, both are pretty good. From what I understand, he was somewhat the equivalent of a "Crew chief" on the #2 car in those years, but I'm not sure how the titles translate over so he may be something else in American vernacular. He mostly writes about his years working on the cars as a mechanic, but he occasionally dives into interesting details and I hear him say a lot of the same stuff you say, it's interesting the different terms the American guys use vs the English guys, but I can tell you two are talking about the exact same things.

SlickTrackGod

I added a botttom paragraph in the above post as you were posting you last message-

TO answer your question- None of us know what we are doing until we collect data after the car is on the track. What makes a good decission maker is experience with data to predict a slight setup changed based on weather and a few other conditions like who else is running that day laying down rubber with what type of tires. ex- we get more grip after running just after the NAPA150 guys our first race because they lay down Goodyear Sythetic Rubber in qualifying just prior to our race on Hossier conventional rubber. The combination of the two make for about 1* more chassis roll on a typical setup we run on a regular race day.

Anyone making decissions on chassis setup need data...period. It how we use that data is what sets us apart. That is where experience and educated guess comes into play. He is my work pad at the track in the back pits. angled uneven asphalt which is very typical. I have this area gauge also and will be cross referencing the tech bay, the home shop, and this pit area with ground levels as the year goes.

Here's also a shot of Andy Pilgram and I BSing late last week. This would be a dream of mine to be on his crew. I just met Andy but he is friends with two good friends of mine athat run at the annual Katech event- so I popped by dropping names and introduced myself- you just never know where something my lead

As crew chief- I basically call the shots. What that means is tire selection, chassis setup and adjustments (within the twam owners budget- we have small budgets, we are not the big bos you see on TV every weekend) I actually call the race stategy and have to guess at how many possible heat cycles of tires via accidents and restarts, I "firmly suggest" to Ronnie in his ear when to get low ont he track to loosen the car, or get up high to let it cool and basically manage the car to last the race and be most competitive. Motor decissions are pretty much non-existant because we run spec motors. I call shock adjustments, I call if we practice or not and what tires to run when to either scuff or conserve prior to race. Their is A LOT of strategy involve in winning a chamionship. I have a 3rd place championship under my belt the only other full year I crew chief'ed. This year is a challange though because we still do not have our prosective sponsor on board like anticipated. Keepijng fingers crossed.

InfernalVortex

iTrader: (4)

Good luck with your new team. Sometimes though coming up with clever workarounds is more interesting... it's a shame when it's more stressful at the same time, though.

What springs should I go with to start? I was thinking 800/200... But I dont know what sway bars it will have. It's a 24mm rear bar and it just makes the rear end come around all the time on me in the fast transitions. It came with the diff... I wish I had kept my 19mm bar but I have no idea where it went. And you said the rear spring rate and sway bar work together. Should I match the spring rates and pick bars to match? Im not exactly sure how the sway bar interacts with the spring rates other than as one gets softer the other needs to get stiffer, but that doesnt address front to rear balancing. Im not sure how you guys really get all this figured out since one adjustment changes everything else.

But I got a ride in a friend's CRZ yesterday and he just hurls that thing through corners unbelievably quickly, no wonder Im losing time. But I just cant go into the corners that hard without the rear end coming around. Im not the most experienced driver, but it seems to me like in a steady state situation where Im just holding a corner at a certain speed (skidpad?) it's fine, but if Im just hurling it in the middle of a transition I can never trust the back end to stay planted. On corner exit the back end will drift slightly outwards but it's very controllable via the right foot. Corner entry I think is where Im losing all my time.

I've also got 275/40/17s in front and 315/35/17's in the rear. I was wondering if that would counteract the giant rear bar, and it did a little, but not much.

InfernalVortex

iTrader: (4)

This is what some other ( ) guy said... I found this trying to figure out spring rates to start with.

https://www.thirdgen.org/forums/post...258-post7.html

What do you guys tend to do when you're starting from scratch? Should I just try to copy GM's front to rear ratios maybe? Usually around 500/100 from the factory I think, right? So maybe 700/150? 800/175?

SlickTrackGod

The loose in problem you describe on post #10 is the typical third gen plow into snap oversteer these cars are notorious for. Your's may not be plowing that much though and is rotating without much overload on the outside front...

What is happening though is the roll axis is out of wack and cantering towards the nose. Upon brake corner entry, the nose of the car dives diagonally over onto the outside front tire/ while simultaneously lifting the inside rear corner of the chassis high into the air (thus unloading the inside rear) you need to drop the rear roll center down significantly at least an inch or more so the car rolls more linear in lean balance front and rear rather than a drastic canter towards the front leaning more that the rear.

This is kindof hard for most people to understand so let me try this visual. Lets pretend you have a hood ornament. Picture if your roll center of the rotisserie axis (think BBQ rotisserie rod) coming out the front of the car at about 2" off the ground, and on the rear it comes out mid bumper(high so the rod angle upward front to rear. Now that low front makes everything above it rotate laeft or right as it rolls. higher up /or further away from the roll center that hood ornament is the more it moves left or right. Now if you raise the front roll center up closer to the hood ornament lets say 5 " off the ground rather than 2", the same lateral force would only move the ornament left or rigth about half the distance in roll travel movement. I hope that makes sense. This is why a roll center variation makes a difference on spring rates and sway bar sizes. Getting the rear down a little (via a Jegs panhand axle side relocator) lower s the rear of the axis (imaginary rod) and extended ball joints raises the front. Now the car roll less...AND roll more evenly to the side, rather than cantering onto the front nose more than the rear.

People do not understand how the front upper weight migrates the opposite direction when a roll axis canters severely.

SlickTrackGod

Now lets look at a swing. it has a top var that supports the swing and chain attachment length. think of that top bar as the direction of travel of the car, and the weight in the swing the cg (center of gravity) of the car in a corner....but its opposite you say? that is correct. This is a perfect example of a roll center higher than a cg (which rarely happens in a motor vehicle- it takes an indy car to pull this off.) But you see how the harder you corner, the harder the bottom of the car will swing out and the top if the chain extended up past the bar would swing inward. This would require a "negative sway bar force" if one existed.

So now lets put the real world situtation back into play where the upper part of the car is heaver than the lower part of the car. The more you lower the roll axis (the bottom bar in an inverted swing scenario) the more the upper will swing toward the outside of a corner and thus the large the swaybar to prevent this force. This is why you do not just lower the rear, but raise the front keeps the roll axis closer to the cg and helps reduce needed swaybar sizes that lock up the chassis and cause a loss in mechanical grip.

InfernalVortex

iTrader: (4)

So that explains why people talk about how lowering the PHB mount does weird things to spring rates and sway bar sizes. Makes sense.

It definitely sounds like what's happening, and it looks exactly like what's happening...



Not sure how I feel about putting a $165 part onto a 9-bolt, but it's definitely something I'd like to do... The rear is an inch higher than the fronts on both sides, will evening out the car help or hurt this? The rear roll center is where the PHB crosses the centerline of the axle, right? So lowering the rear WILL lower the rear RC, right? Just not very much? Im guessing the front roll center just gets lower a lot faster than the rear per inch drop. So the ball joints will raise the front RC back up to line it up with the rear a little better.

Suddenly some things make a lot of sense. The slight 1 inch rake the car has is hurting it too. The back has to come down.

TEDSgrad

iTrader: (4)

It's only $82:http://www.jegs.com/i/Jegster/550/41055/10002/-1?parentProductId=754011

9bolt will hold for what your doing. The cones become a wear item, and parts get expensive and you'll have to get good at shim measuring. I'm in the in-between land where I really want a wavetrac, but....$$$
I have 850/200 set-up, and will probably move to 950/200 and I have an aluminum block. You should definitely up your front spring rate.

Our older design is still very capable!! Use RC height as a primary tool to control roll angle, THEN you need stiffer springs to load the tires more. Modern set-ups DO NOT use RC to control roll angle, but do use RC to primarily load the tires more. Two different strategies, both capable of getting the job done.
So, control roll angle with CG & RC adjustments, add more spring to bring back more load to the tires; and find the balance that makes you comfortable/predictable.

All this talk of rotisserie: "We Hungry!" - Fast & Furious quote.

InfernalVortex

iTrader: (4)

The UE PHB relocation bracket has brackets for both sides of the PHB and it has a big reinforcing bar on the axle side. It just looks like a really nice piece. After looking a little closer, it seems the jegs piece also includes that brace. So maybe that is an option. But is the UE method of lowering BOTH sides of the PHB superior?

I even have a Torsen T2R for a 10-bolt on a shelf.... Fortunately last I checked my cones are in EXCELLENT shape, but that was a couple of years ago. Who knows what it looks like now. It still passes the torque test with one side on the ground and the other side in the air.... I think it started to spin around 40 ft lbs?

It definitely seems like this is the answer for what Im dealing with.

InfernalVortex

iTrader: (4)

The Jegs bracket only lowers the axle side. Am I giving up a lot by only lowering ONE side? The rear roll center is where the PHB crosses the centerline (Im guessing both vertical and horizontal) so if I lower both sides then I can get the rear roll center even lower...

Is this preferable? Is there a "too low"?

SlickTrackGod

The axle side is all you need. The chassis side one is for stock height cars only. On the UE kit, the stock height 4th gens need to have both side lowered at their ride height in order to keep the panhard somewhat level to the ground. A 3rd gen slightly lowered is enough not to need the chassis side.

To give better reference, my car was 24 3/4" fender height up front and 25 7/8" rear- I had the panahrd in the second setting down and still had two more holes to go that were not being used on the bottom of the Jegs mount.

You can run heavier rear srping swith a shorter tqarm (Im talking 275 range) and drop that panhard down 2" and still be fine witht he jegs unit.

SlickTrackGod

Also note the more you lower the rear rc (compared to the front rc), or raise the front rc up with extended ball joints- the steering will feel heavier and heavier the more you flatten the roll axis parallel to the ground.

InfernalVortex

iTrader: (4)

So are we aiming to keep the panhard level? From what I remember from your posts, a lowered thirdgen will put the front RC (or is the IC?) below the ground, so why dont we want the rear roll center as low as possible? is it due to weird jacking effects? Or is it just that the swing arc of the PHB is too exaggerated when it's not horizontal?

Now I think Im seeing why you want me to raise the front RC at the same time.... Im not gonna be able to run extended ball joints with the springs I have... it's just gonna be too low to keep the car sitting level. So that's gonna have to wait until i actually get my weight jacks done, which is going to be a little longer now since I've made this PHB bracket a priority. I've already found a guy to install it for me, was just waiting on someone to chime in on whether I should go with the jegs or the UE one. Im so glad to hear you say you use the Jegs one!

So just so that I'm clear on all this... I want the panhard bar to be perfectly level from side to side? Or do I want it level, say, under braking/turning when the rear of the car is going to go up a little bit? Or do i want to set it on the lowest setting possible?

I read something from unbalanced engineering saying that they just expect people to put it in the bottom bolt hole and leave it... but that may have something to do with their bracket on the other side. BIG_MODS ' car has his pan hard bar a few inches above the ground, and completely level and in the pictures of his car turning it definitely doesnt look like it's got an inclined roll axis.

Having the roll axis parallel to the ground is the goal right?

Im also so glad to hear you say that I can work around a short tq arm. I dont like crossmember mounted tq arms because I just dont think the factory sheet metal at the crossmember mount is worth a damn. So Im stuck with a short one. The fact that you say I can tune around it and that you didnt say to throw it in the garbage is pretty reassuring. I still have the factory arm for now due to my reservations about where to go on that one.

So when I get the bracket welded on, I should set the PHB level, and then I should go up in spring rate and down in sway bar size? On frrax they said something about getting Koni DA's on the rear to adjust one of the settings for more compliance... Ive already got Koni yellows, I'd love to hear you say they're just fine.

And as for how low the car is now, it's not low to most, but it's low to me. I do have plans to bring the rear end down, hence the weight jacks I started the thread about. I just wanted to be able to control spring rates, and I didnt see a point in investing a rear weight jack setup if I didnt also devise a way to come up with front weight jacks... I would have been stuck buying the Ground Control kit anyway after buying my own rear setup. This all lead me down this rabbit hole to PHB relocation brackets...

Front ride height is 26.5, rear is 27.5 on seemingly flat ground. Im not sure Im willing to go to 26" or less with these wheels. 17's stick the outer shoulder pretty far outboard.


Also Dean, you may get a kick out of this, I run #46 because of a certain NASCAR movie from my childhood.

TEDSgrad

iTrader: (4)

The relationship of the roll axis - Fr RC -> Rear RC - that is important.
Also, it is weight above CG in combination with roll axis. Unless you're planning on fiberglass hood, plexi glass all around, gutting interior; lowering the PHB both sides is just a waste. Use the jegster axle side, experiment, and if you feel you have to do both, you haven't lost anything - add in the other side. If you go for both and stiffer springs and you don't like - you're out springs and have to cut off the pass. side bracket. Your car. My advice - incremental steps and learn from them. This is not a track dedicated car, right?
Parallel at compression! - not static stance. 1" is an accepted split.

SlickTrackGod

No you don't want the roll centers (and overall roll axis lower to the ground. you want it close in relation to the cg of the car. The lower it gets away from the cg the more the need for heavier swaybars. Heavier sway bars loose mechanical grip and lack wheel motion independance from the chassis.

Like Ive stated in the past, when you lower a 3rd gen, the front rc goes down faster in proportion to the rear rc. At stock height, the front is too low already when at OEM chassis specs. This is what causes the notorious push/ into snap oversteer these cars suffer from.

Whan a roll axis is lower from the cg, every hard pressed steering imput on edge will be much less controlable unless really heavily dampered (high rebound shocks to control body movement roll) When the rc stays closer to the cg, the lateral roll is lessened and habrupt steering imputs do not create alot of chassis attitude change in the form of loading the outside wheels.

With all that said, you do not want a neutral roll setup either where the roll axis and cg are the same. This would never yield any chassis set when cornering. When pertaining to driver feedback, a loss of touch with the car would be felt. Kind of a false security. The car could often sometime have a feeling of "high siding" like a motorcycle will do- this would happen if air got up under it at the wrong moment, or if you hit a bump and unload the chassis just as you were entering a corner, etc. The comfort of a little 'set' in the chassis when cornering is a comfort thing to help a driver judge the amount of grip is left. Now too much of this causes upper polar movement of chassis weight (remember that hood ornament) and will lean abuptly and snap back resulting in 'tossing" the tire lateral grip into traction loss- thus generally a plow condition where the car squeals and understeers.

RC changes are something everyone needs to feel for them self. Youc an not teach it in words, you have to buy the jegs unit and play with it in a few different setting and realize yourself how each little adjustment changes the whole feel of the car.

SlickTrackGod

Here is a great example of rc's and roll axis-

I can not get my front RC any higher in vetruck. I cut off my stock front suspension years ago- yes CUT OFF, and I welded all new suspension mount points and fabricated my own front suspension geometry, Whith that said, this is as high as I can get my front rc in this truck and you see it is not leaning from too low a rc, it is leaning because frankly, a truck is tall and just should not be doing this. I have a lot of upper roll weight witht he tall roof and the roll cage. The rear is lighter and lower (big problem) because in essence I need to invert my roll axis, but with a long wheelbase and a detroit locker- I would never be able to get it to rotate. You can literally see in this picture the front and rear of the truck fighting eachother trying to twist the chassis like a pretzel. I have about 300lbs of metal I weleded into the frame of this truck as well as the aporx 400lbs of cage as well. it is quite rigid- it was not built to be a racecar, it was built for safety on the street and to haul heavy loads- but yet it happens to run very well on a race course for what it is. Notice how as the truck leans it is just lifting the inside front wheel- if I choppped the roof off it would not do this.

ps- ever wonder what a 295 rear tire looks like when it yells "oh sh*t" because 5000lbs is leaning hard on it? take a look at that 2nd picture.

Base91

iTrader: (1)

Steep learning curve here! So I'm not sure if it was verified that one goal is to have the roll axis parallel to the ground. That would seem intuitively correct but is it really the case? Also, if the cg is lowered (eg 2") is the roll center also lowered 2" or is there a different relationship? What heights are the cg and rc of a stock 3rd gen and how are they calculated?

InfernalVortex

iTrader: (4)

From what Im gathering....

1. the roll center must be close (But not too close?) to the CG. If you lower the car 2" the CG will lower some amount less than that. (Im assuming CG takes into account unsprung weight here)

2 Due to front suspension geometry, the front roll center drops more than 2" given a 2 inch drop. Im not positive, but I think it actually goes below ground level when you lower these cars.

3. The rear roll center is higher from the factory, and does not drop much at all for a given drop. so the inclined roll axis is exacerbated by lowering the car, and makes the car prone to push, then snap oversteer on cornering.

If we want the roll center to be close to the CoG, then why are we lowering the rear roll center? There's no way that the line where the PHB crosses the axle centerline is in line with the center of gravity for the car. Is it purely a compromise to deal with the front roll center being so low? I really dont know?

This is BIG_MODS' PHB...



And I think Im seeing here that the roll axis is NOT inclined. Obviously this is not a street car, but it's just interesting. Just a different setup than stock to compare.

SlickTrackGod

No, you do not look for the roll axis to be parallel to the ground. There is no reference point. It is done by tires temps and or feel of the chassis by the driver.

This is why there is not one universal spring rate combination that fits all. Whenever someone asked about spring rate choices, It has everything to do with style of driving, chassis weights, shock dampering, rear diff, chassis stiffness, tire sizes, and yes roll centers as well as the fine tuning of what sway bars one might have or be using.

Basically in steady state of a corner (mid corner grip) you can say that a car with 600/225 spring rate combos and 36/19 swaybars would/could attain just as much lateral grip as a car with 800/225 and 36/23 bar.

What is the difference? #1 the panhard would be higher on the 2nd combo. #2 the front compression dampering would be higher with the 600 rate car, #3 the static negative camber would be higher on the 600 car because it would yield more suspension travel and roll in mid corner set, etc, etc.

It's not about what you have, its about using adjustments to set it properly. You do not shoot for a "specific roll axis" tht is preplanned so to speak. That is what the big automakers now do, BUT, ultimately the work done on paper then needs to be sorted out in real world testing on the test track to fine tune all of these things a computer could never do. Ferrari has all the money in the world and the best of the best educated technicians and engineers- yet they still take 150 of their best to the track to sort things out in the real world before any magazine article, race, or media event.

Now to get to ride height and roll centers, the rear moves down with the car as it is lowered in linear ratio. examples: you lower the rear of the car 1", the rear goes down 1/2 of that or 1/2". You lower the car 3", the rear rc goes down 1 1/2", etc.

Now the front rc on the other hand is a progressive advancement in ratio. I do not have exact figures because exact figures will vary greatly depending on ride height AND alignment specs combined- as well as the variance of adding aftermarket parts such as extended ball joints, raise strut mounts, wider track width of front tires, dynamic movement of the front suspension (meaning how much travel your spring choice makes) based on overall chassis weight (variance again on V6, V8, fiberglass hood, alum bumper support, etc, etc, etc) as well as shock damper rates and elapse time of braking and corner set...as well as baking grip intensity and brake coificiant. ....I know, this is turning into a head splitting novel- but you are starting to understand why no one can tell you exactly what spring rate is best for your car unless you try various things and do extensive testing.

....But, fior sake of arguement, the front lowered 1" will take the front rc down 3/4". The front lowered 2" could take the front rc down 2 1/4", the front lowered 3" could realistically put the front rc into the dirt lowering it 8".

Now when it comes to a rear rc adjustment using the Jegs panhard relocator, a 1 bolt hole drop (1"- but a 1/2" rc movement down) can and usually is a BIG movement of adjustment. Sometimes on my racecars I use just an 1/8" adjustment to fine tune and get some heat from the fronts to the rear tires. I am changing the complete setup on our race truck right now from example. I am going from the setup my team owner had using 200 fronts and a 175-225 rear rate split with a panhard 1" split on the chassis side being lower--to-- a 325 front 175/275 rear split with a pnahrd 1" height split off the ground favoring the chassis side higher. Yes a 2" panhard movement on the chasis side (because its on the right side and we only turn left. I use some panhard geometry angle to pull the chassis down in corner set)

SlickTrackGod

You lower the rear when the car is lowered BECAUSE in ratio the rear rc moves up comared to the cg height of the car. I listed above how when the crear lowers 1" the cg goes down 1" and the rc only goes down 1/2". While the front is going down faster and faster progressively as you lower. Thus the front comes up AND the rear goes down- more important for the front to go up though, but thats based on geometry of parts and alignment, etc.

Look at Big Mods pic here, you can see a heavy lean on the entire car in roll. His roll axis is too far from his cg. Ok for the slow speed stuff, but get some higher speed sustained g's and the car will be a handful with conrer set bobble as well as will suffer greating in ride quality going staright line due to the high spring rates. Vetruck suffers badly when empty, but it was built to carry heavy loads most all the time. My stright line comfort is not needed because it is not a daily driver for empty load comfort,. When I need comfort, I thrrough several bags of sand near the tailgate and several up front near the cab. (3 up front and 2 in the rear of the bed)

Study the rear tires on his car, and then compare to the pic of my truck above. I have twice the weight he does. His car is full strpped race car with a cage, but it is purpose built and is probably 3000lb range. I am not purpose built, I am a full weight street truck very tall and heavy that is built heavy duty for durability- no one bit of emphasis was put into lightning anything. Look at the tire sidewalls of each rear tire, and look at chassis set onto them. he has alot of lean for not having alot of tread lateral offset on the rear wheel. His weight is coming down on the outside and coming up on the inside tires. Mine is going over and down, and the inside is weight leveraged more (in the rear only. My front is lifting from the massively high teeter totter)- I think I may have to do some sketches later to explain this better to everyone. I have to run right now.

Base91

iTrader: (1)

You are very patient. I'd been thinking a watt's link would be good for the rear but it looks like the level panhard bar can be set lower than the center of a watt's link could be and this would be preferable? And cheaper?

InfernalVortex

iTrader: (4)

Dean... I think Im starting to understand here....

CG is where your weight is acting on the suspension. A low roll center will force more and more of that weight onto the tires unevenly. IE too much load transfer. If the roll center is high, closer to the CG, the whole car will rotate around the RC and center of gravity yet all the tires will stay more loaded, getting you, in theory, twice as much grip.

So it's not about putting the roll center high or low, it's about getting it matched up well with the center of gravity. And Im guessing if the roll center is EXACTLY on the center of gravity, the car wont roll at all no matter what you do to it, so it's much harder to feel what's going on with the car. The "set" I think you call it? For the driver's benefit?

Now Im researching extended ball joints... looks like Im in trouble with a 17x9.5" wheel. I wont be able to fix the bump steer that results and Im limited on how much lower I can go.

hellz_wings

iTrader: (2)

I have HOWE racing 0.75" extended ball joints up front, MOOG iroc springs.. With a LS1 brake kit that pushes the wheels out 0.3" (further raising the RC in relation to the CG because of the wider track width, albeit slightly) and front fender heights that are about 26.5" to 27" up front varying by side. The rear of the car is lowered slightly with cut MOOG iroc springs (3/4 of a coil) but I have 4th gen isolators in the rear so it's only at 27.5" to 28" fender height varying by side.. I installed UE's rear PHB relocation brackets set to the lowest hole on the axle side, and the body side is 1" higher at static height. I've said in other threads that the car wobbles too much out back and has very bad transition response because it upsets the chassis too much because of all the rear roll. The car has a tendency to understeer on corner entry if I take it too quickly unless I over throttle it and kick out the back (which is hard to do with good tires with this setup, but do-able with good control). (I have an iron block and head V8 so the front is heavy, although I have the battery relocated out back.)

The solution to this would be stiffer springs out back, and to lower the front a little more and lower the back alot more to balance out the front and rear RC (by lowering the front slightly and lowering the rear CG to be closer to the rear RC, which should balance the front -> rear RC difference..) Add to that, stiffer springs out back, I'm thinking 165# voghlands out back, and this should help alot to balance the handling (plus lowering the CG always helps out with weight transfer). I just don't want to go too low because this is primarily a street car.

InfernalVortex

iTrader: (4)

I thought Roll center was dictated by the ball joint and the lower control arm mounts? I didnt think tire location had anything to do with it? If that's the case then my wider tires have raised my front RC a little.



I did a bunch of digging....

Herb Adams says this:
I dont know who herb adams is... but if nothing else it's a reference frame.

BIG_MODS posted this:

I thought that was pretty interesting.

Im thinking I wont be able to fit a ball joint that long... so my gains will be less than that. He also said some things about how he didnt think that would really make that much of a difference that you couldn't compensate with tuning other parts of the suspension. I dont know about that, but I do know that my car isnt as low as BIG_MODS' car, so my RC isnt going to be under ground. So it's probably around ground level.


So they're on my list, but they're on a waiting list.

Im going to get the Jegs bracket. When I lower the rear RC I need higher spring rates in the back and a stiffer sway bar. So Im wondering if I should go ahead and cut half+ coils off the rear springs and put my factory isolators in there to get the spring rate up. And it would address my way too big sway bar issue. (34/24 right now)

Dean, in what order should I get extended ball joints, the panhard bracket, and aftermarket strut mounts?

hellz_wings

iTrader: (2)

When you have a wider front track width, it lowers the front CG, therefore bringing it down closer to the front RC (Sorry I didn't explain this clearly earlier), it doesn't have any affect on the height of the RC.

SlickTrackGod

yo lost me on that one. You actually had it right the first time. The centerline of the wheels is were the rc calculation geometry comes back across the midline to. The wider this is the higher it will cross the midline. CG is the weight of the car. it does not change unless you lower the car or reposition mount location parts Ie move the battery, drop motor 1" etc etc), or lighten parts. Other than that simply adding track width has nothing to do with cg height. or weight bias.

Infernal- The Herb Adams stuff you quote is the same thing I was talking about where you say he states "jacking effect" and I stated "high siding". You want to make sure the suspension never raises enough to get lofty and get the dynamic rc above the cg in travel or else it will get real funny on you. This is why you keep it low static and make sure where it goes dynamic--> because dynamic it changes, NOT ONLY height, but it will migrate side to side also- THIS is the real key. THis is why I ised progressive rear springs to migrate my rear rc to the outside of the car under corner load and increase the teeter totter leverage of weight onto the inside rear wheel.

The only thing I will question on your Herb Adams quote is say a figure you need to shoot for like the 1" below ground to 3" above ground....
reason #1) Is he talking static rc height, or the overall migration?...exactly- who knows, its jibberish.
#2) what is the height and overall cg of the car in topic Herb Adams speaks of? Is it an Indy car? is it a Corvette? is it Vetruck? is it a Semi truck? again who knows. There is no exact range for al cars to shoot for. Just forget about his quoted range.
3) lastly, pertaining to #2- what is the range of rc's to cg on each axle of the said car? again, who knows.

That Herb Adams quote is quite inconclusive.

SlickTrackGod

Niow to give a quote of mine: I would say without any real world actuall data on my car specs- just assumption (I did things to feel, not paper calculations) I would gues my cg was about 16" off the ground and my front cg static was about 6" and my rear at about 10". Overall my cg to RA (roll axis) leverage length averaged 8" static.

Now in dynamic motion my car did not move. I had an average corner "set" of 1" with a 1 1/2" max documented front wheel travel (yes my car was light and hardly moved). The front RC would drop maybe to about 3" off the ground and the rear would come down to about 9.5 (again, just an estimated guess) So it would go fro, a 4" aprox rake to a 6.5" aprox rake pf roll axis angle from static to dynamic.....
...but most importantly, here's a real key point---> My rear RC would migrate right on a left hand corner (and visa versa) because of the progressive rate rear springs changing load weights- rc will favor the higher rate spring on a solid rear axle setup) and thus the inside rear becomes much more heavy than a car with conventional linear rate springs. This is what I do witht he NASCAR setups also. I run a heavier rate spring on the outside rear than the inside rear to get this leverage by "yawing" (pitch, roll ,yaw) the roll axis going fore to aft in the chassis.

Just looking at this quick sketch, you are looking at the body of the car and the rear RC point (viewing from behind the car) and how it's positioned in dynamic form (under conering load) and how if you could just put the body into static form like this the left of the chasiss would weight more than the right. This is very advance to understand this scenerio as well as to try and draw it so you understand what all forces are going on. This is simply showing teeter tooter leverage, not car lean or lateral load.


I am the only one to run progressive spring successfully because of my understanding how and why to use them to my advantage. I have never seen anyone else here understand of put this to use. With the progressive rate rears, I reduced the spring "unload" pressure because a progressive spring looses energy quicker as it unloads than a linear spring. Thus because of that, I had enough build of rate to prevent wheelhop, yet I did not suffer from jacking effect under long braking zones like these cars are notorious for, as well as (here's the kicker)- I could run my car close to the edge in static form getting the rear RC up to the cg without suffering from lateral jacking if the car hit a high speed bump and unloaded. There is so much going on here that I do not know if I could get a V8 car to do all this without first trying- I never did that and I do not what you running out buying this stuff chasing something you would have to rely on me to help sort out an unknown. Its just with this discussion you are having a better understanding of what "possibly " could be accomplishjed if you know what you are doing. I was successful with my car becasue it was a very light weight nosed V6 and 1) had very little travel, and 2) better weight bias, and 3" had very expensive light weight parts for unsprung weight and small wheels 16x8. Wheel weight is critical in unsprung weight and handling.

SlickTrackGod

My last point on this thread would be some info so that you are more understanding and not discoraged at the posts I just made.

The topic of this thread was about "Front Weight Jacks". The principle of having weight jacks is so whatever spring rate you put up front you can redial the car to the same exact ride height it was before with another spring rate. This sets of course the static ride height only, not the dynamic height. Dynaimc height is the statte the car is in under corner entrance, then dynamic state of mid corner balnce, and lastly the dynamic state of the chassis coming off the corner. ...

Now, changing spring rates up front and setting them to the smae ride height will keep the alignment specs the same in static form, but will most definately change the tire footprint in dynamic form. THUS most likely the car needs to be realigned to that new setup. What alignment? only testing will know- you need a pyro and a crew to get tire psi, tire temps, and shock travel indicators so you can see what the RC is doing and what each wheel tavel is in relation to the others. It takes years to sort out a car and lots of parts, AND lots of trial and error. I am helping give you the understanding and the knowhow tools of what to look for, not the tools to do it right the first time- that does not happen. Front weigth jackers is just a tool for spring changes without ride height changes...period.

Now to give an example of real world testing, In our last Supertruck race, I could obsevre Ronnie (my driver) giving up time on the track going into each corner (turns 1 &3 of the oval track) When he is next to other veteran competitors with seasoned cars, he can not brake as late and as hard as they are, When he does, the softer front spring he had onthe truck he just bought were creating a good amount of brake dive (I have antidive upper control arm angle maxxed on the front right side) and the front suspension was standing on the nose increasing the roll axis as well as the dynamic cross and would go to a loose puch poose push bobble that made havoc for Ronnies steering imput under braking. Under soft braking the rear has time to set down with the front as bank compression forces gain into the corner. I could do two bandaid things to help this section of track- one is until we hit a bump in the middle of 3-4 and go tight, the other os good until we come out of 2 & 4 and try to put the power back down (we'd get wheelspin.) the forst is to rais ethe front compression rate of the shock valving to slow the sudden brake dive of the softer rate front springs, and two would be to yank the rear end down with a 3rd link change- both would fix tht section of track, but would cause problems elsewhere. It is better I increase the front spring rate and change the leveragge of the rear panhard to balance the mid corner state while retaining the same rear springs. Long and short, that give a little very basic example of spring changes. I will have to start with a little more static neg camber up on the RF tire because it will lack camber gain (in the more limited nose travel into "set") but that I like because I run the straights more on the inside edge of the tire which helps cool the mid to outer rubber for the next corner-WHILE ALSO giving less straight line friction since braking is done more on corner entry under slight turning with no stright line braking. The track yeilds the drivers lift the throttle for a second and initiate the turn-in just prior to having to brake bofre they need to advance more steering imput into the bank.

InfernalVortex

iTrader: (4)

I feel like my car weighing a good 300-400 lbs more than yours means that the sacrifice in unsprung weight in wheels is worth it to get more rubber on the road. My next build will have aluminum heads, and that's really the last obvious thing I can do to get the weight down, and the car should be in the 3250 range at that point.

Im an engineering student, and Im only about halfway through but I've already taken physics, statics, dynamics, so oversimplifications of complicated dynamic situations isn't foreign to me. It's just that race car dynamics are a whole different field all their own. Writing and solving an equation isnt the answer. Figuring out how to balance dozens of different load situations in the most optimized way is.

hellz_wings

iTrader: (2)

Dean, yes, ofcourse I meant the wheel centerline (not track width), as it goes wider the CG goes down, my bad! lol..

SlickTrackGod

Very true. Most cases a wider track car will not be a problem on a large high speed road course, but an autox type course will hurt transitions.

Also remeber that Cadillac didn't reduce unsprung weight for ride comfort, then INCREASE SPRUNG weight- which is basically the same but at a cost of more strain on tire wear. Wider tires do not necessarily mean longer life, most of the time it is shorter life because all too often people run on only parts of that tire widdth. I have had many descussions on here in the past about using a smaller width tire to its fulest is better than a wider tire.

WIth that said, the wider tire will in fact run quicker pretty much every time- but at a cost. it will wear out very very fast and most often very uneven. Even if the front wear even, they well wear out faster then the rear (that is what I also mean wit uneven wear.) In a lengthy race, or a track day with multiple run- you'd better have a large pocketbook if you want to go fast with big wide tires. I would rather loose a little but last all year with something that is actually lightweight and functioning.

I would also take a 2000 lb car with 8" wheels over a 3000 lb car with 12" wheels any day of the week for a duration race. Autox is known for slapping on wide meats and running 60 seond blasts, not 30 min intervals with long test sessions also.

SlickTrackGod

Not cg, RC goes up. CG stays the same always.

This is a loaded statement also. With extended leverage ont he spring rates, the travel compresses and the CG goes down. The dynamic position of the RC will change greater also as a result of wider track width.


Now if you mean leaving the track width the same-Outside wheel lip to outside wheel lip- and simply using wider negative offset wheel then yes the rc calulation points where the centerline of the chassis is crossed will lower the rc.

SlickTrackGod

Sorry Base, I missed this.

Yes a panhard cound be set lower. A mumsford could be set even lowest witht he rear RC in the dirt.

A watts link gives a very predictable feel. For that they are good when it comes to driver feedback. Lonnie has one and will attest to this.

Where I do NOT like a Watts link over a panhard is you can not manipulate the watts to migrate the folcrum point of the RC towards the outside to yaw the roll axis like you can with a panhard rod.. that pivot point on the watts is basically it. Everything in the rear rotates in it. The panhard is an imaginary point that can dynamically change- I like using that to my advantage to wieght the inside wheels. It a panhard is setup long enough and correct geometry, it is a predictable as a watts. A watts will work in a wide range of ride height, a panhard will not. Thus you need the panhard long and limited travel.

hellz_wings

iTrader: (2)

Yes you're right again! The wider the wheel centerline, the higher the RC goes (closer to the CG) because of how the wheel centerline intersects with the instant center (in the pic I attached which is pretty clear on how this works).

This actually also shows how lowering the car changes the a-arm angle and drops the RC lower than the amount that you drop the CG by lowering (as you explained above).

TEDSgrad

iTrader: (4)

Remembered this little visual:

Base91

iTrader: (1)

Watt sure was an engineering genius. Based on the lowering geometry diagram, if you lower the front with springs only the cg drops a little, the instant centers and rc drop a lot more and the roll couple is larger. Lower cg sounds good but the rest doesn't. If you lower with drop spindles the cg and instant centers drop the same amount but the roll center drops less so the roll couple is reduced which sounds good. So to get the roll center back up closer to the cg the spring height could be increased which would move the instant centers and therefore the roll center back up. And that would be good? If that's wrong it's back to study hall!

SlickTrackGod

Very close. The spring drop is correct. The spindle drop basically leaves the rc the same but drops the front cg 2". Drop the rear of the car 2" also and the rc goes down 1". you have is essence raise the front rc 1" compared to the stock roll axis angle, the cg has come down 2", and the cg is closer to the roll axis.

The only potential problem with the drop spindles is increased scrub radius (fatter wheels/tires could possibly cause unwanted wandering under hard braking). I address this in another post about using them with slightly extended a-arms and a more negative offset wheel. The problem is the tierods...maybe, I never got that far. to experiment any further so the rest is assumption on where I might have gone with the car in the future.

SlickTrackGod

Understanding the visual of roll centers and the roll axis is the holly grail of understanding what a car is doing in 3 parts of the corner (entry, steady state, and exit)

Once you grasp this and start to visual it, the rest is history.

Play with an small empty rectagular kleenex box or such and a pencil stuck through it. move the pencil through it at different points, even yawing the rear exit of the pencil and rotate the box on the pencil axis. You will learn A LOT !!!

InfernalVortex

iTrader: (4)

It all transmits through the tires, though. Is the goal to spread the load as evenly through all four tires as possible? or to somehow portion out the load to the tires with the most weight against them? How does the polar moment of inertia play into all this? Since it cant be easily changed is that something we just ignore?

I need to read some of those books all the road racer guys tell me to read...

SlickTrackGod

Polar movement can be in X, Y, and Z axis (roll, pitch, and yaw). Usually when i discuss polar movement I speak of yaw (corner transitions of the chassis forward path changing directions as in going through a slalom course). In the case of roll axis, the polar movement would be "mosty" roll and pitch. THe more the "pitch" of the roll axis, the more the yaw movement of the front of the car comes into play when the front roll center moves further away from the center og gravity. i hate to go here with you right now- this is very advanced imaginary thought and will further cluster your brain right now. lets stay with basics and ignore the polar inertia for now- but yes, ploar inertia comes into play dramatically like in the case of my Vetruck that is very tall with a heavy cage in it reaching tall in weight height. When looking at the truck from the front, the top of the truck will move left or right off centerline quite a bit because of the distance of the overall height of the vehicle. It's like a figure skater with their arms out to initiate a spin, then bringing them in to incerease rotation speed and reduce polar movement- then back out with the arms to stabilize and slow the movement coming out of it. The weight here of course does not move closer and further, but the polar movement of any weight further away from a movement axis takes less to yeild the same inertia as that of twic ethe weight only half the distance away. Weight moved into the center of the vehicle is optimum.(height, for and aft position, and side to side position. Get everything you can in between that wheelbase. That is why the V6 handles so much better becasue the engine is completely behind the front wheel axis, and is lighter in roll weight.

What are we after? We are not looking to eliminate roll. We need a little bit of roll to set the outside wheels into load. Why? Are you a snow skier? do you ride motorcycles? either one of those is a great example of how weighting the oputside foot makes for better grip in cornering. Ahhhhh you say- so we just want to weight the outside tires and forget about the inside tires? yes and no.

Here is why-(and then I will next get to the real answer of what we are after in roll axis height increase). With all that said, if you are a road race type car (just like a slalom skier) you go from edge to edge left to right to left to right.The more you weight that outsie edge, the faster you go.....to a point. You eventually can't hold that edge anymore becasue you fatigue (ie- tires get hot) and the more you press on that one outside ski it will eventually slip from too much weight/pressure on it( so you balance with the inside ski slightly to recover (you hope)......I now have the greatest question for you: do race tracks have equal amount of lefts and right hand corners? 100% of you should have the answer NO. otherwise you would never make it back to where you started. Do race tracks have the same acceleration points coming out of and going into left and right corners? Also NO. A drag strip would be equal accelration and braking. On a road course we have off camber corners, decreasing and increasing radius corners, bank corners, etc. lets take a racetrack now that goes clockwise ( connects back around to the right). That would mean the lefts take more load in general and thus more heat. Same with autox, they are not drag strips- they generally favor right or left tires based on the direction of the overall loop connection.

Ill post this for now so I do not loose this- will continue next post

SlickTrackGod

Now because of the reason explained in the last post, one tire on a car will in fact wear out faster than the other three tires- unless you really get lucky and have an exact perfect balance to accept the chamge in fuel load, brake heat fade, and changing track surafce grip and temp in a time duration race five minutes long or more. Yes the car changes in usually just three laps at most on ANY track. The longer the race, the more the change/ So again, usually one tire will wear fater then the other on that side of the car- if it doesn;t, I assure you the next race it will if you change nothing except run a different time of the day.

So what do we do to help prevent this? we try to distribute the weight beter so all four tires accept heat and grip rather than just the outside two. They will not run as hot, and they will last longer. HOWEVER, if you do this too much or the wrong way, the outside tires will load onlly from the side without downward force and you will not have grip (remember the skier and the motorcycle rider. A motorcylce gets better grip on those only two tires by weighting the outside peg of the motorcycle so as to put load down on top of the tire. If the rider weights the inside peg the tires load sideways and loose grip. THIS IS WHY WE DO NOT WNT NEUTRAL ROLL or in other words do not want the rc and cg the same height off the ground. We want a little bit of roll to set the outside tires.

OK, so now you say a lower RC is better then right? NOPE. Why? becasue you need a larger swaybar to counter act the roll force from going too much. Here's my next simple question: why do dofferent cars types require different sway bar sizes and combo's (meaning does a corvette use the same size swabar as a Ferrari, or a Nova? Nope, they all need what is required to control the makeup of the chassis design roll weight....

....Everybody thinks the massive 36 mm front swaybar is the Holly Grail of 3rd gens. That is a massive bar to counteract the deficiancy of such a large positive roll weight the engineers inadvertantly made into these cars. 36 is huge for a street car. Its like the old Chevelles and such running the hugh 1 3/8" performance swaybars to try and somehow contain all that screwed up engineering of the 60's and 70's.

Lets start getting to the point- 1) we want to load the outside tires without using such a parge swaybar that ultimately des nothing more than locks up any independance of individual wheel travel over bumps, and 2) we want to stil weight those outside tires while finding ways to weight the inside tires also to assist heat management of tires and grip.

(here's the punch line)You can have the same exact load on the outside tires with lesser diameter swaybars WHILE ALSO having more load on the inside tires as well.

here is an example: You take (and these are hypothetical but I assure you they are close) two cars the same exact weight, motors, tire size, I mean everything identical twins. You have lets say a cg 16" off the gorund and the forst car has a RA averaging 6" off the ground with 36/24 swaybar combo ( "dynamic" spring rates identical on both cars for sake of ease of examples- note I say dynamic). the second car has lets say extended ball joints, progressive rear springs, shorter sturt towers,.... basically it has all the same type of parts, just altered settings and heights but pretty much everything bolts in the same and is the same weight- so its cg is the same 16" but its RA averages 10"-------------> yes this one only needs a 30/19 swaybar combo..................and BOTH cars roll into a set of 3* chassis angle.

The difference is, if the outside tires take 100% of their capacity (meaning at full grip just before loss of traction, they are both being pressed over with body roll) the car with the smaller swaybars takes more cornering force to get to that 3* roll angle becasue it is carrying more load on the inside wheels then the car with the larger swaybars. The smaller bar car may be carrying 60% of its potential 100% traction, and the other car may be only doing 40% on the inside tires- again while both cars are taking 100% of outside tire grip.

Now this is important- note that if you start taking the rc too high closer to the cg- lets say 16" cg and 12" RA average, the outside tires may not laod on flat ground because the car will maybe only roll to 2* and then loose lateral tire grip and slide. the tires outside tires would only reach about 75% potential grip.

SlickTrackGod

How the car weigths those tires is all about roll centers and roll axis in relation to the chassis weight and specificaly mostly it CG- however, yes polar weight if roll motion can and will produce more inertia on corner bobble of the chassis when hitting bumps. I suffer bady from this in Vetruck. Listen to it in this video at 1:00 exactly into the video on a downhill off camber corner. you'll hear the tires chatter as the polar roll wieght bobbles. This is one heavy pig. (ps- the announcer's comments are quite humourous- He later discovered who I was from years ago in my Vette) They had never seen Vetruck at local autox I was there with a few thrid gens and decided to throw it around the track- May want ot fast forward to 0:50 becasue the first half is too far away and boring).
I can not take my RC any higher to counter the tall roll leverage. I am on edge as we speak and this truck will in fact sometimes highside a little on high speed bumps which makes for a real scary dance for passengers- I know what to expect becasue I've driven it for years, but trust me it will scare the living heck out of someone with a little side to side nose dance at 100 mph sweepers. I keep referencing this truck because the larger something is the more previlant the roll characteristics will show. If you study if you can physically see how it rolls and can pinpoint the roll axis just by watching it. It is the perfect example of "polar roll weight" (as in roll , pitch, and yaw)

SlickTrackGod

Polar Movement in roll.

I have discussed how the chassis will motion right when youturn left, and vica versa.
The best example of this I can give is by looking a a clock on the wall. If you look a a clock, think of the center of the dials as the roll axis and the car is going away from you.
Going stright, the chassis of the car is up right at 12 oclock. If you turn left, the body leans to 12:02, if you turn right it leans to 11:58 (lets say 3* each way)

Now the size of the clock makes all the difference. If you have a 1foot round clock as opposed to a 3 foot round large wall clock the amount of movement is different at the 12 oclock opoint of the dial. On a 1 foot clock truning left, the dail leans to 12:02 and moves right off center about 3/4". On the 3' clock that same motion would move the dial off center about 2 1/4". This is polar movement in roll.

This movement is counter productive when trying to get a car's mass to change direction through steering. This movement is what delays the response of a car to transition and is the motion of which the suspension needs to absorb and control prior to getting the weight to go the other direction (the direction of intention). the lower the cg from the rc, the more this movement is and the great the size of swaybar needed to control it. If you increase the resistence with spring rate, you will only further unlooad the inside front wheel- thus the swaybar is needed to lock up both sides to the chaassis to prevent rol---but also at a cost of locking up independant freedom.

People will put bigger tires on their car to go around a corner faster. All this does is increase roll angle from lets say 3* to 4*. So now we are lifting even more off the inside tires. So what do most people do? they put on heavier springs and heavier swaybars- wrong move. they just locked up the car from conturing the independant suspension to the ground and provided a harsh ride. yes it works, but at a compromise of ride height and mechanical grip. the sider tire grip is more advantange then the loss of grip of the stiffer springs, so the final outcome is worth it even though onw is a postive and the other a negative....so, why not try and get two positives?

We know the wider tire will advance lateral grip of a tire being pushed sideways (ie outward instead of downward) so we can gain grip without needing as much roll weight sitting on it. Thus, reducing the leverage of the cg to rc will produce the same roll while increasing grip without having o up srping rates. It's a win win. Just don;t go too high. There is a reason why every fast car you see is low to the ground in overall height. There as very rare exceptions like this Renault F! chassis with a minivan attached up top. and a huge wing- but this thing defies the laws of physics to me. QUITE F'ING IMPRESSIVE!!! Keep in mind it is a F1 car. The upper body weight is minimal when you compare it to an actual street minivan that is identical. I would be apt to say they put a CF look-a-like body onto it. There is absolutely no roll even though Prost is seated up high.