Suspension / ChassisQuestions about your suspension? Need chassis advice?
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PLEASE DO NOT ASK PERSONAL QUESTIONS ON THIS THREAD_PLEASE START YOUR OWN THREAD WITH QUESTIONS.- however, pleae feel free to add info here or challange any info posted. This is an open forum.
Before I go into chassis bracing. I want to first get into front geometry and an inherent defect we have in design from the factory. It will intel these 3 topics and pictures for reference.
SAI (steering Angle Inclination)
IA (Included Angle)
Scrub Radius
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Last edited by Vetruck; 09-28-2009 at 12:51 PM.
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If you study the last picture above (Scrib radius) you will see that 3 things we do performance wise affect the scrub radius.
1)Wider wheels and tires
2)Wheel offset
3)brake hub offset (in regards to brake package upgrades pushing this mounting face outward)
The factory srcub radius is set from design engineers at GM and was not made to be altered. Unfortunately, the designers engineered this setting to 15x7 factory wheels and tires and standard Delco-Moraine caliper,10.5"rotor package.
Later, GM designers modified the platforms intended use by fitting the cars not only with 16x8 wheels, but also using a slightly more positive offset 1LE package brake setup. This increased the scrub radius more positive.
The end result? How many of you have experienced you factory 16x8 wheel car lifting and the front wheels fighting eachother in a low speed parkinglot full lock turn to the left or right? Everyone of us. It is a factory flaw, an inherent defect in design.
The more positive this scrub radius gets, the more the tires drag the contact patch on turning, the more the Ackerman angles fail to provide inner and outer matching turn radius' and cause Toe-in conditions which all 'jack' the nose of the car. Toe out squats it. You really in all times want "dynamic" toe nuetral setting. to get this, we have to alter static toe settings and factor in things like tire distortion, bushing deflection, drag and setback as a result of such (but we are getting into a different topic. Back to keeping the tires from scrubbing as much.)
So now we go to SAI, steering Inclination Angle. What determines SAI? The angle of the strut to spindle does combined with camber specs.
When Camber adjustment up top (via- strut mount adjustments) is set so as the spindle is parallel to the ground with the wheels pointing straight and camber is at 0*, we have the SAI and IA matching right? NOT ALWAYS....
....Factory tolerances in machining the spindles AND combined with the slight play in the 2 large bolts that mount the struts to the spindles will often if not always a difference from side to side. Our SAI on our cars is roughly about 23.5* from vertical.
Decreasing IA will bring the tire closer to the strut body, whereas increasing it widens the clearance but looses IA. The play in bolting the strut to the spindle slighly differs wheich in turn differs the SAI and the IA when camber is set to 0* on both sides.
So how do we fix it? We technicaly are not suppose to have adjutment here, so an alignment technician will not correct this if you bolt yours together yourself upon installing new struts then taking the car for an alignment. So here is what the basic person can do when torquing these bolts is to insert the bolts on both sides whereas when you torque them they both draw the SAI to its maximum slop readings. Usually people install these and torque one side positive and the other side negative due to the rotation of the nuts on the spindles and bolts- be contious of this slop between the spindle and strut in regards to SAI.
(note: this writeup is obviously not for the average suspension enthusiest, but is necessary for all out handling- Hece again my topic "Ultimate 3rd gen suspension")
Now how do we fix this for ultimate handling? well of course one would now think we need to go further with this adjument right? but there is none. We want to increase the SAI so that the line draws to the ground more outward towards the centerline of the now wider tire contsct patch....
... So we can slighly elongate the spindle holes...at a price to pay. We loss overall negative camber potential.
Here is our limitation factors we need to look at.
1) since IA and SAI is now increasing, we gain clearnance for the tire to move inward in offset- thus decreasing positive scrub radius-GREAT, but only if other tolerances allow.
2)However, we need to be concerned with brake caliper clearance. Generally, this will always be the limiting factor of wheel offset choice. Wheel width is what you choose, and scrub radius goes positive to that wider tire footprint as a result of wheel offset and width combined with tire size choice.
So how do we bring the scrub radius closer to the tire center contact patch?...
...by moving the "unmoveable" IA.
How do we move this? I mentioned one way above in elongating the spindle holes..Or...Intrax sells a kit they mistakingly call "a camber kit" which actually should be called an IA kit. Intrax Eccentric bolt kit part # 99-9-014 $35.99 @ Summit Racing http://www.summitracing.com/parts/IN...4/?image=large
{I am going to submit this so I do not lose this novel}
But at a price to pay in loss of overall negative camber as mentioned above. This will require a marraige of componants to pull off the proper geometry.
If the initial SAI is about 23.5*, with this kit we can increase the SAI to lets say safely 25* on both sides.
(NOTE: You now have adjustments for this and can pay your alignment tech extra money to loosen and move this adjustment to bring the SAI up on both sides but most importatly exactly equal (I will get into the importance of being equal in the final conclusion)
With the IA higher, the outer edge of the spindle is angling towards the ground (and visa versa), so concequently when you move the spindle angle back up to parallel the ground (0* camber) the SAI increases.
Marraige of componants.- At this time you probably definately have run out of adjustment on the camber settings. this is where conponant choice purchases can help and come into play.
1) ride height. base on products used, the lower the car in general will bring the A-arm up and increase the angle of the strut shaft yeilding a better Negative camber max. (as well as caster)
2) using a product like Spohns adjustable A-arms with spring perch will give you a slightly longer A-arm rendering a slightly better strut angle. (Important Note- too much adjustment on the delrinadjustabvle length ends will render the coil spring hit the sides of the can- this can be bad. test fit to gain lentgh but not interfer with clearances needs to be performed.
3) proper clearance of any offest strut mount to gain as much negative camber needs to be researched. you will have to decide your particular needs as to how much scrub raius derease is needed for your particular application of wheels, A-arms, strutmount choice, IA,etc and if really needed you can go to Ground Control's offset sturt mount inserts for added negative camber.
In conclusion, The affects of positive scrub radius' on a driver is the scuffing of the contact patch and consequent traction loss. It also has a major affect in steering imput especially if one side of the front brakes is working less it can cause the steering wheel to want to rip out of your hands. The more positive from neutral the scrub radius is the more undesireable steering imputs the driver has to fight.
if your tire has a contact patch on the ground (lets just for ease of disscussion say) is a square patch 6" wide and long and a neutral scrub radius has a plotted point oright in the exact middle of it with 3" fore and aft and well as 3" left and right that swivel around the center point when turned. Now if you move that contact patch outward 3", the center plotted pivot point is 0" inside and 6" outside left to right. When you turn the contact patch you are scrubbing a greater radius of 3 more inches being the highest total of 6" off center pivot wheas the original was only 3" off center pivot at the greatest point away.
All of this now a greater track width with new wider tires and wheels- even though now has a corrected scrub radius, now has to be married with an equal rear track width for neutral balance in cornering. The tires front and rear need to follow the same path. If the rear tire is outer, the car will turn loose, and visa versa. Keep the same front and rear overall track widths. If the front increases by 3/8", then increase the rear 3/8". Check rim lip width to rim lip width side to side on both front and rear and space the rear equal track width too the front.
Also, with the corrected scrub radius, the Ackerman angles will not close as much, but adjustment in bringing the spindle archs closer together laterally in mount in regards to sprindle steering arms is not adjutable (for the most part, I do not know of a kit that will correct this. you want the outside spindle steering arm to shorten while the inside arm lengthen in geometry) but is relitively a very minor decrease in ackerman. It still should be about 12* on the inner wheel if the outer wheel is turned to 10*.
[note on turnplates and Ackerman. If the car is placed on turnplates with both front wheels pointing 0*, you then turn the outside wheel to 10* and the inside should be at 12-13* range. the wider the track width the higher this goes, but BARELY like from 13.0 to 13.2. Not like it goes to 15* or something crazy.
In other words, I would not worry too much about Ackerman, its good enough for goverment work.
Here is a picture showing the IA change where the top of the strut is angled more towards the engine bay and the scrub radius decreases towards neutral.
The strut angle is the SAI. (thick black lines)
Camber angle is vertical in both with the spindle 90* from verticle- thus camber is 0* in both.
The IA increases in the bottom pic- its the angle from the spindle(vertical) to the steering angle inclination (SAI)
Now note: to increase camber -1.5*, you would increase strut angle 1.5* increasing the SAI 1.5* also. It all moves in realitive form.
That was fun, but I am tired for now. I have computer-itus and need a break.
I really appreciate all of the time you are putting into this. I have a dedicated autocross third gen that I run in CP and I believe I will find this info usefull. Looks like right now the most important part for me to get will be dropped spindles from part 1.
__________________ I started racing when I was 7 years old and here I am now... KONI Yellows | Pro-Kit | J&M Strut Mounts | Edelbrock STB | Spohn SFC | 9-bolt disk 3.27
36mm/24mm | UMI Adj LCA/PHB/LCARB | Corbeau seats | plus more ...and I'm only 18
could anybody make this and his previous thread into one and make it sticky ?? i will be needing all this info when prepearing my car into drift and it will be easier to find all this useful information
Thank you for the compliments. SLP-GTA, I have barely any studies in Engineering other than HS math and drafting, and 1 college course 20 something years ago in CAD (computer aided design).
Most of what I learn is self taught through trial and error and a drive to win. I am very competitive.If you feel your car, it is usually talking to you through virbrations or noise.
I have years of watching racing as well as driving various tracks in time trial and club events. I started out always on go-karts, offroad stuff including I could go forever on an enduro type motorcycle in a wheelie till the front wheel stopped rotation- then the gyro stop would cause the bike to yaw. I never had the money for sanctioned road racing events, I could not afford to have my car crashed into.I have always stuck to more open track events and time trial against the clock...
...with that said, racing gets boring under rules and restriction unless you race yourself against the clock. My biggest challange was not other people in my class, it was being the fastest car out there. Nobody is watching the slow cars on the track. I just like all out running for the thrill, not trohpies. I also like being an underdog bringing down the guys with expensive cars, big engines, etc with something that is a sleeper- how do you do that? by carrying your speed. never having to slow down means never having to speed back up either- That's handling.
You know when someone beats you in a drag race and you just know you can't catch them? That's what I like to make people feel going around a corner- I am gone, then they try and reel me in on the next straight when I out brake them (smaller, later braking zone than them)and gone again in the corner.
Back to the point? You feel your car. If the front is handling better than the rear? look for anything to get the rear handling better. Once the rear is better than the front, get the front handling better. Sometimes you start learning there is a give and take, sometimes not. Something like the SAI,IA and scrub radius I mention above? well the alignment shops give you a printout with them on there- Do most of us ever stop to think WHY ARE THEY ON THERE? and what do they do? Maybe they have reason. Years ago I learned these reasons through studying any car spec or term I would come across- searching for better and better grip. The best book I had was Freds Puhn's "How To Make Your Car Handle" but it was very confusing at times. It also never really explained what affected what else when you changed something. I leaarned most of this from going to the autox track and trying it with results. Suspensions is just a hobby of mine, but I do love teaching it because it was so hard for me to learn I feel there is no book out there that describes things well now that I know vehicle dynamics. Most of the stuff is all over the internet also now days, no need to really buy books, just research it on google and such. But it is still hard to grasp without someone like me putting it into "our car's example" so it is better understood.
When you guys and gals see these things I write, you are now better understanding why my little V6 it handled so damn well. All the little things add up. Attention to detail.
My favorite quote-
"Its not just what you've got, but more importantly how you set it".
Enough of the pep talk stuff. But I hope that talk motivates some of you, suspension dynamics is fascinating- people I talk it to look at me sometimes like I am some kind of rocket scientist- I did not invent this stuff, I just learned how it works.
This should definitely be a sticky... I'm reading all this info and trying to comprehend this knowledge! It's so complicated man... I appreciate the time you put into this Vetruck! I'm also contemplating getting 2" dropped spindles from Racecraft to lower the car rather than lowering springs! I'm also gonna buy everything adjustable as well.
Thank you!
__________________ "An engine is like an orchestra. It's made up of wind, brass, percussion, and a whole range of other complimentary sections, all working to make that beautiful music that we call 'performance'..."
We have 2 basic styles of Sub Frame Connectors (SFC's)
1)Internal mount units like Alston's etc
2)Outer rail (what I call perimeter) style SFC's like most of the popular aftermrket vendors sell.
What is the difference? well the inner units are narrower mounted laterally (They are closer together in side by side mounting) under the car and span a distance front to rear without any connection or ladder bracing (Guys like MADMAX(Chris) could probably put this into better terminology than me. I do not know all the structure terms). In other words, Alstons can twist easier. They give good fore and aft bracing for drag race style bracing straight line (as do the other perimeter styles) for lifting the nose of the car without chassis bending downward on the nose as much, but serve no purpose in lateral twist of the chassis needed for cornering.
Perimeter style SFC's I feel are far supeior in design and yes they DO (against popular belief) tie both front and rear subframes of the unibody together.
What I like about SOME designs (I had Spohns tubular units, I will use those for my example since I bought them for this reason- some others will do the same also, but not all) is the ability to stitch weld the SFC's to the unibody rails along their span of the chassis (unlike Alstons design). Also, they hav one side bar that ties intot he main tubes on each side that connect accross tot he inner subframe near the trans tunnel. Both of these features (1-stitch welding in increments, 2-ladder bar type connector inward) ehlp prevent the fore and aft tubular support from twisting. I have had a few serious debates on my theroey of Sq tube perimeters deflecting still. Large enough sqare tube also ladder braced will not, but at a price of extra weight compared to round tube. But this is still debatable, and I will leave it at that other than my car did this (picture attached) with round tube SFC's stitch welded and 1 ladder bar connector on each side). The chassis was so stiff without a cage in the car boxing the chassis demesionally it teeter totter'ed on curbs just with Spohn SFC's installed as I described.
Caging any car and dimensionally boxing its structure is by far the best-( like any race car tube chassis does) but adds major weight to an already heavy unibody chassis structure. In a race car tube chassis, the cage IS the chassis, whereas, a cage added to ours is just a smaller cage structure added to an already large unibody chassis with subframe.
More bracing to come.... If anyone could find me that famous picture of the underneath a bare 3rdgen on the rotisserie that would be great. One withOUT any sketching on it. Thanks- just post it here if you can.
In response to the chassis part... I have installed both MAC (like the alstons) and the SPOHN (outer) frame connectors... I first installed the MAC ones and the car DID handle better, but with the spohn ones it feels more boxed and more like the rear follows the front in the corner... There's literally no flex anymore.
__________________ "An engine is like an orchestra. It's made up of wind, brass, percussion, and a whole range of other complimentary sections, all working to make that beautiful music that we call 'performance'..."
pic
This one has SFC's welded in, but is it the one you want?
Wow that is an amazing pic of the underneath of our cars.. thnx!
__________________ "An engine is like an orchestra. It's made up of wind, brass, percussion, and a whole range of other complimentary sections, all working to make that beautiful music that we call 'performance'..."
What about the other braces I've seen on your car? Care to explain those or how different parts of the chasis move when under strain. Example: how do the strut towers move/flex when you turn or go over a bump? I know I've read about the mods to your STB and how an adjustable wonderbar helps due to the preload you can put on the front frame horns. Can you go in depth about that kind of stuff? I could try to explain it, but I'm sure you could do it better.
The best book I had was Freds Puhn's "How To Make Your Car Handle" but it was very confusing at times.
Probably the best introductory book to this stuff I've seen, even if you sometimes have to connect the dots for yourself. Got mine when it sold for $5 new and I still refer to it.
I hate to just post "subscribing" if I can write something at least remotely useful to somebody.
What about the other braces I've seen on your car? Care to explain those or how different parts of the chasis move when under strain. Example: how do the strut towers move/flex when you turn or go over a bump? I know I've read about the mods to your STB and how an adjustable wonderbar helps due to the preload you can put on the front frame horns. Can you go in depth about that kind of stuff? I could try to explain it, but I'm sure you could do it better.
Mike
Sorry everyone, I have been busy. Matter of fact I am heading out of town late tonight for the weekend. I will get to those other braces, but first the STB
Strut Tower Brace (STB)
Why is it important for a 3pt brace? there are two main reasons I have witnessed. One is the flex of both towers in unison laterally even when tied together with a 2pt STB, triangulation of the brace via a 3rd pt is needed to prevent this. The other reason is the flex of the strut towers towards the firewall- Believe me this happens, I have felt it when I removed the 3rd pts entirely with the rear inside tire loosening, as well as with it back on and the factory Edelbrock brackets flexing under a stress test I did with a cardboard jig that broke.
One MAIN point of car sturcture everyone needs to know and not dispute (if you think I am wrong then research car design)....The windshield is in fact designed as part of the Chassis structure in strength. YES, the windshield acts as bracing.
Now we go to the 3pt STB and how it ties into the firewall at mid windshield. Let me just draw pictures and show the difference between the 2pt and 3pt braces.
this example will show how a 2pt STB will still flex in unison laterally while a 3pt STB will help prevent this lateral flexing of the strut towers.
NOTE: if both towers still flex together in unison it is
1) still changing both camber specs thus changing predictable footprint contact patches,
and 2) This is minor but it will also slightly change the track width of the outside contact patch edges following the same path in forward direction or travel. This will loosen the car even if this only moves 1/8" inward and then flexes back- it puts unwanted steering imputs by the driver- makes a driver work harder.
IMPORTANT NOTE: With factory rubber bushing strut mounts, any STB is USELESS. A STB's basic design is to maintain solid camber specs so they change predictable through articulation eliminating unwanted flex in the chassis. The inside tower is in theory supposed to brace the outside tower as a spreader bar. Those rubber factory mount flex internally- no bracing of any STB will stop this- Change your strut mounts to solid bushing mounts.
Flexing shown here may vary depending on the integrity of each individual chassis and its resulting metal fatigue. What point of lateral g's does this occur? I guarantee by 1g of tire grip it is flexing.
Tube type- There is round tube and sq or retangular tubing. Which is best? Pound for pound round tubing is better. the same guage 2" square tube is heavier than 2" round tube.
So if you take the same weight tube You can use thinker smaller dia round tube as opposed to thinner larger square tube. Its all a compromise. Take your pic.
I am just leery of thin gauge square tube still flexing under twist. I have had this arguement with a few engineers on FRRAX.com to no avail. It is too hard to get my point accross and I am no metalologist. I just know what has worked for me. I also in my shower business have torn out numerous square tube aluminum shower frames to see them twist like no tomorrow. I do fabricate, and weld and have ALOT of "amatuer" experience with metals. I just like round tube stitch welded in increments along its span to the floorboard mounted on the chassis perimeter. I think pound for pound square tube will still render flex fore and aft- I KNOW MY TRUCK FRME RAILS DID- and they are beefy retangular tube. I have had to ladder bar construct them not to twist- we can not do that on a 3rd gen do to poor subframe to ground clearance.
Style? as mentioned - perimeter chassis type like in the picture GregZ-28 was so kind to find for me. You can clearly see they do in FACt connect the front and rear subframes and they trangulate inward towards the inner subframe structure of the trans tunnel. I will highlight the factory subframe.
Red= factory subframing
Blue= Perimeter style SFC's with inner frame connectors.
Yellow= stitch welding to chassis rail lip in increments to prevent bowing of span. Bowing of the chassis will help allow twist still.
Green= solid trans mount supporting rear trans tunnel flex.
Next is my custom lower rear A-arm lateral brace. KB (Kenny Brown) once made one that never really sold. He marketed it as a trans tunnel brace and I think most people never understood how and why it was made due to the name.
Under high lateral g's, the a-arm mount ears on the subframe take a load pressing them inward - just like the upper strut towers do. These however, really take the blunt of the tire grip force and put massive lateral pressure on the lower rear portion of the front subframe (or the front of the trans tunnel portion of the subframe)
IMPORTANT NOTE: The front A-arm ear tabs are laterally supported by the K-member. In fact they are intergrated into the K-member and do not need any type of bracing. For this matter- I recommend keeping the factory beefy k-member for its super strong bracing of the engine weight and front portion of A-arm lateral load.
To the rear A-arm brace.. It needs to be made for removal! Design here is your own creativity- mine worked, but bent the brackets and had poor swivel attachments- but it was better than nothing. I used preload here. Because the A-arms are under tension to squeeze the rear tabs together under braking loads (when the tires want to stop and the center chassis wants to keep going).
You see here in the attached pic the brackets Iwelded to the subframe in green (also in green is the rear solid trans mount as mentioned before) Gray is the aluminum spreader bar with rodends for preload OUTWARD.
IMPORTANT NOTICE: You can get away with swivels here because if you notice the position of the bar is directly below the ridgid firewall so as not to have one mount raise higher than the other vertically.They can squeeze together without the bar, but they can not deflect up and down because of the firewall flat palin structure. Also NOTE: The factory subframe ties laterally inward to this brace from the SFC's most frontal portion. Complete lateral strength of the tunnel and SFC's prventing center chassis twist due to tunnel colapse.
Fore and aft positioning of the RAB (Rear A-arm Brace)
is fitted under the Bell housing/TQconvertor gap. It is the only room to spread the frame rails directly behind the oilpan and in front of the trans.
Steering box brace OR "Wonderbar"
It is a little spreader bar setup GM actually engineered as a baidaid fix to the factory cars fitted with wider tires. Wider tires meant more force exerted through the linkage to turn them...hich in turn meant in reverse fashion that the steering box was forced against the subrame railsflexing tthem and thus eventually cracking the box from the subframe. The Wonderbar braces the frame rails from flexing and eventually cracking.
It works pretty good, but in my opinion needs more help the higher the lateral grip and higher the turning force climbs. What did I do further? Well, I had the lucury of LOTS of room in the engine bay of a 60*V6 where all of the engine sits behind the centerline from spindle to spindle. I had room for a lateral brace behind the steering box attached to the subframe.
IMPORTANT NOTE 1) You can not do this the same way on a V8 car- motor extends too far foreward.
IMPORTANT NOTE 2) This again like the RAB has to be removable so it was made with swivel ends and preloaded OUTWARD just to put tension on the sibframe to prevent flesing in or out. Why outward? That has room for debate- Some will argue that the front of the A-arms should preload inward, but that is lower on the K-member which will NOT flex inward or outward under brakingor lateral load. this brace is merely for the steering box. The strut towers are also adjacent to the subframe here and they need to be kept spread for the camber, so I, figure why pull this inward. Preload it outward. Just keep solid tension on the steering box rail so it does not flex.
Result? My car had steering imputs like a damn jetfighter! I had 4 front lateral braces
1) 3pt STB
2) RSB (this Rear Steering box Brace)
3) RAB
4) Wonderbar (which I installed and tack welded ridgid so the bolts would not slip and loosen possibly- if I ever needed to remove it I could simply grind off the tack welds)
Well we could go in several different directions.
Unsprung weight and its criticalness to ride and handling quality Vs. wider heavier wheels and tires for more grip- I will leave this up tothe individual. I happen to like WIDE tires, but low weight and wide cost big bucks as well as fitment issues already address in part 1.
We could go brakes? Larger brakes control heat better, but too large run too cool and increase unsprung weight.
Again, Lightness is money- refer to my custom brake build where I fitted 6piston Wilwood radial mounted calipers and 13x1.25" aluminum hat rotors with custom made Global West G-body (yes G-body) Aluminum hubs designed for a 4000 lb g-body road race car.
While you are adding modifications to your car, most people are doing just that...adding weight. SFC's, wider tires and wheels, extra bracing, bigger this, bigger that.
To fight this we can reduce weight as well as keeping in mind we want to also move weight to a better 50/50 front and rear bias (so the tires laterally bare equal weight loads) as well as the all important POLAR weight removed from the extremities of the cg (or center of the car in movement transition. Taking 10 lbs of the bumpers is better than taking 50 lbs out of the passenger compartment. I have done a novel awhile back on polar weight- let me find that link:I'll just copy and paste that text here. I wrote this on these board back in 2003 under the name AGood2.8
"I posted in another thread about "polarweight" Its an important agility factor to great handling of any vehicle- I have never heard it discussed and figured since I mentioned it, AND I"M BORED RIGHT NOW, I figured I'd explain its importance to anyone that is interested.
1st off, polarweight is weight relation to the center of axis or gravity in rotation. What this means is the further from center of gravity something is, the more force that is required to move it/ or stop it.
Example- (as we all know) Hold your hands close to your body and twist your hips left and right and left... You can stop one direction and reverse into the other fairly quickly.
Now hold your arms extended out sideways and twist, it now takes more effort to stop and reverse directions, Or just to start the twist movement for that matter. Hold weights in your hands and it gets worst.
How does this effect handling? In a big way. When a car turns into a corner, the front and rear bumpers and/or the side doors are your hands held extended outward. That weight rotates on the car's CG (center of Gravity) when it turns left or turns right. The more weight and /or the further outward the weight is placed, the harder it is to turn the car (and to stop the car from turning after initiated)
Example: Lets take the battery. We can all move a battery around anywhere in the car. Most relocate it to the rear when dragracing to get more weight over the backend. If that battery weights 30 lbs and is sitting in the car right ontop of the CG, then the polar movement weight is 0. Move it up to the stock location (aprox 5 ft estimate based on most cars{note: every car has a different CG- My V6's CG is further back in the wheel base than you V8 guys}) and the polar movement weight is now aprox 750ft/lbs. at 2 ft from CG it is 120ft/lbs and so on.
Moral of the story- Any critical parts to the car that can be mounted more towards the center of the vehicle rther than the outer extremities (like the battery, and MSD box, big frickin speaker boxes, anything....) can help inprove the slalom speed of the vehicle. "
Examples of polar weight reduction-
The elusive factory aluminum front bumper support- I had one.
Reduction of the heavy rear muffler and exhaust routing- I reduce it with a custom Stainless Steel Exhausts I-pipe muffler that was 26.5" long and replaced the I-pipe. It ran parallel to my 4" round CF driveshaft and fit no problem. I eliminated 40 lbs of exhaust and muffler weight reduction off the back of the car.
Roll weight? The higher the part, the more critical. Windshield glass to lexan, fiberglass hood, etc.
Since therre is far more roll weight above the cg, focus on reduction below the cg is a mute point.
Tube type- There is round tube and sq or retangular tubing. Which is best? Pound for pound round tubing is better. the same guage 2" square tube is heavier than 2" round tube.
So if you take the same weight tube You can use thinker smaller dia round tube as opposed to thinner larger square tube. Its all a compromise. Take your pic.
I am just leery of thin gauge square tube still flexing under twist. I have had this arguement with a few engineers on FRRAX.com to no avail. It is too hard to get my point accross
Unless/until it buckles, a round tube IS more efficient at carrying torsional loads, at least in terms of the stress distribution being uniform. And it's more stable in terms of retaining its cross section shape when loaded that way. I don't think anybody questions these things, either over on FRRAX a couple of years ago or at any of the other places where this topic has surfaced. [V6RSR, right?]
But BY ITSELF, a small-diameter thinwall round tube (think 2"/11 ga and smaller) does not add much torsional stiffness to the chassis (think 10%, just to get an idea). It needs to work with the rest of the chassis structure, and it's here that the picture about which shape is better gets a little cloudy. Questions like how much torsion vs how much bending come up. It very well may come down to "ease of fabrication" eventually counting for more than shaving off the last few ounces per foot.
No, I wouldn't use a sharp-cornered extrusion in any structural automotive application either. That's just asking for trouble.
I really wish we would not ask questions like this here on this sticky. Could you please ask them on a "NEW THREAD". This clutters the postings of "the ultimate 3rd gen" base platform with modified questions that most would not ever be concerned with link 3rd links. Thanks. Once you do, I will ask everyone to transfer their postings to that post and erase this one.
So, is this all you would do for additional chassis bracing in the average street car?
Now, what if we took it a step further and added a roll bar/cage? Where would you tie into for mounting points and how much would you add? Basically, at what point does the added weight/complexity of the cage outweigh it's structural benefits?
Also, separate question but still on topic, would you do anything differently for a t-top vs a hardtop car? Any idea how much the t-top guys are giving up in chassis stiffness? Or is it minor enough not to matter, especially if properly braced?
Cages should be your basic boxed trangulation for rigidness. The main squarish cockpit box should be tied into thr SFC's I feel but most regulatory sanctions want them plated top the floorboard generally with something like 6"x6" plates.
Fore and aft bar strutures are the tied into the upper load points of the suspension that apply force into the chassis.-those points are the strut towers, and rear shock towers areas.
With any cage added, weight goes up as well as roll weight. the necessary modifications for weight reduction will be needed to counter act this added weight- Remove glass, strip interior, etc...basic stuff you would do with any car- nothing specific here for 3rd gen.
I would not build a t-top or convertable unibody chassis for handling.
So you don't feel that even properly caged and braced a t-top chassis is still no good?
Wouldn't the proper amount of cage triangulation make up for the loss of a full roof?
Or at that point does the extra weight added offset any gains?
And for the record, I do have a hardtop car. Just trying to further explore the topic of chassis stifness and how it relates to handling.
I have a t-top car and it handles great... Subframe connectors added on will make the chassis very stiff, I have two frame connectors and can say it's stiffer than most hardtops. This just means added weight but you still get the benefit of a stiff chassis so i don't think t-top cars really are that much worse in the handling department as long as the chassis is properly braced and things are done to keep the weight down.... Two sets of frame connectors probably weighs around 40lbs (20lbs each). You can offset that easily by installing 4th gen seats which are approx. 40 less than 3rd gen seats.. AND the seats sit higher than the frame connectors so you would actually be adding weight lower than the roll center where it counts and removing where it's useless (above the roll center).
Also, I know you can't do this for drag racing (I don't think) but taking off the t-tops and putting them in the t-top bag over the rear wheels adds traction and the weight is lower there as well. So, t-tops are not that bad for handling but do require more to stiffen the chassis and keep weight down than a hard top.
MY 0.02$!
__________________ "An engine is like an orchestra. It's made up of wind, brass, percussion, and a whole range of other complimentary sections, all working to make that beautiful music that we call 'performance'..."
So you don't feel that even properly caged and braced a t-top chassis is still no good?
Wouldn't the proper amount of cage triangulation make up for the loss of a full roof?
Or at that point does the extra weight added offset any gains?
And for the record, I do have a hardtop car. Just trying to further explore the topic of chassis stifness and how it relates to handling.
Whats the point of having t-tops or convertible after it is caged? Get my point?
Anything can have enoguh metal added in the right places to eliminate flex- at a cost of weight.
A unibody is just that...a unibody which means the chassis and frame are one together. Ever see the cracks on the roof of a hardtop? The chassis takes strain through the roof. If I caged a car, I would plate the cage to the sides and roof. I am doing that to my Austin Mini Cooper.
I am joining the two structures together to eliminate flex of both with two smaller units assisting each other rather than flexing independantly. I can't tell you how many cars I have witnessed the cage inside the cockpit flexing about the shell. I have had my fingers grasping on cages an feel the flex of the gap to the shell.
How do you prevent this? Either build a heavier gauge roll cage, or keep the lighter weight one and tie it into the shell.
Now tie a lighter cage into the shell of a t-top? the t-top is flimsy. You will need a stiffer cage for a t-top car than a hardtop--whether it is tied into the shell or not. Same goes for a convertible. However, a convertible can have a strong thick cage because there is no upper weight of the shell. Remove the convertible top parts, etc.....and you have one bad *** car. But who in there right mind is going to butcher a convertible to dry use only and eliminate the top entirely for a daily driver? not many.
This subject has again taken the topic of 'ultimate 3rd gen suspension' off course. It boils down to personal preference of car one wants to build. heck, I see people building 4 door whatevers into road racers- whatever floats your boat. There is nothing pound for pound as good a structure as any baseline hardtop chassis for ANY model of car. They are the lightest and strongest rationally speaking. (Yes there are exceptions to any rule, I do not what to see those clutter this post). Convertibles are heavy. You do not want to strip them? Then do not use them for ultimate handling. Nor would I ever use a t-top unibody. ps- I own a t-top vette--It however, sits on a frame, not a unibody.
conclusion- 3 cars identical with identical modifications WITHOUT cages and full interior comforts.
A hardtop
A t-top
A convertible
The hardtop will have the stiffest chassis. PERIOD.
What are you comparing it to when you say 'it handles great'?
How do you know it handles great, it might handle better than what it did before, but on what scale is it great? This is a worldwide forum. Please post #'s.,...I can.
great to one person can simply be an opinion or a limited experience level, and can be boring to another person.
I am not here to embarrass anyone, I just want you to think twice before you continue this discussion, you may end up embarassing yourself when I simply start asking you to back what you say with a list of questions I will want you to ask. You may have just eliminated rattles fro a little while longer.(ps- I have seen your other post) I would not call that 'better for handling', you did nothing for chassis twist. Its like a thicker tape measure will project outward further without bending than a thinner one, but they both still twist. Anti twist is what is also needed for chassis x weight maintinance in cornering.
I think alot of you know, but there is alot that do not know about the local So CCalif gridge match and smack talking that went on here a few years back. The topic of who's faster and what can a car really do (especially in this case a little 2.8l 60*V6 on stock wheels vs many other local modified street cars- all on street tires) I had an ongoing $500 slalom challange I posted and never had any local takers. I ran this autox smack talk grudge match for free to prove a point. Here was the "morning line favorite's" concesssion statement after that event-
{"Again…I have to congratulate Dean.
That is one hell of a vehicle he’s got. To simply call it agile would be a grave injustice; it’s more like a slot car. Hey its just like the warning label says on the back, “On a Rail”…yeah he’s not kidding. Weight is definitely a key factor in his vehicle set up and proof to point, the V6 is a key contribution to the lethal blow this vehicle delivers. He bought my books, dragged my *** to school, shoehorned my *** into a desk, and gave my *** a straight up education. All things equal…the car itself is always the determining factor and yesterday he had the better car. Well done Dean my rusty sheriffs’ badge still hurts…"}
Great can be a personal assumption....and usually is.
Obviously the hardtop car will have the stiffest chassis. Not at all what I was getting at. I was basically looking for input in this thread on chassis bracing as to what you would do if you were prepping a t top chassis. And what, if anything, you would do differently vs a hardtop car?
I ask because around here t top cars are much more plentiful as donors than hardtop ones and thougt it would be interesting to hear from someone who is obviously knowledgable what they would do if starting with such a platform.
As to why, why not if you're building a max effort street car. Some people like to take the t tops out for a nice cruise every now and then but still like to get the most they can out of their vehicle.
Just thought it would be interesting to discuss. Didn't think I'd get a why bother answer.
And yes, the last t top f body I caged I did tie the main hoop into the center of the roof and also tied the sides of the cage into the sail panels. I too have seen the cage flex separate from the rest of a car. That particular one had a 700 rwhp twin turbo 383 so I did all I could to strengthen the t top chassis.
I've done plenty on dragstrip and all out street cars so I have knowledge and experience in what I'm talking about. Im just now starting to get into setting up a car for open track use. Hence why I was looking to have a discussion with someone who is into handling and how chassis stiffening could/should be applied to the different chassis we have available in our platform.
In short, yes we all realize a hardtop is better. But, if you really need to have t tops, in your opinion, what extra steps should you take in relation to chassis bracing. Chassis bracing was the original point of the thread so it seems like a relevant question to me.
My apologizes if I was not clear, I thought I answered your question for you.
A thicker cage, or just more bracing as needed.
I would simply start by installing a thicker gauge cage.
Just keep testing the flex of the chassis by jacking corners and taking measurements. If the chassis is flexing? Then keep adding more triangular bracing in the direction of the chassis flex.
You could remove the rear seats and do some lateral "ladder bracing" through floorboard tieing perimeter SFC's together better to prevent twist.
I have a t-top car and it handles great... Subframe connectors added on will make the chassis very stiff, I have two frame connectors and can say it's stiffer than most hardtops.
The added stiffness from SFCs that you feel in your seat is not necessarily the stiffness that helps tune the handling the most efficiently. What you're really after is torsional stiffness, and that pretty much ends up having a 3-D solution. Things like wide, deep sills or a boxed tunnel is ons possibility. A proper space frame is another. A platform with deep diagonal bracing yet another. The OE coupe/hardtop is more or less a space frame, with the roof rails and windshield/hatch headers being part of this. Cut the roof rails out and replace them with a single strip down the middle of the roof and the load paths are now nowhere near straight, and the structure simply can't be as rigid without being lots heavier.
I think that sometimes, class rules regarding cage design and attachment are intentionally written to keep cages from being too good at adding stiffness. Trying to walk the fine line between having a chassis that's production-based vs something that's nearly a pure scratch-built tube frame (silhouette) car.
My apologizes if I was not clear, I thought I answered your question for you.
A thicker cage, or just more bracing as needed.
I would simply start by installing a thicker gauge cage.
Just keep testing the flex of the chassis by jacking corners and taking measurements. If the chassis is flexing? Then keep adding more triangular bracing in the direction of the chassis flex.
You could remove the rear seats and do some lateral "ladder bracing" through floorboard tieing perimeter SFC's together better to prevent twist.
Thank you. I understand what you are saying about why it's not ideal. Just wondering what steps you would take for those that have to have them.
When jacking would you go to the outermost edges of the unibody or the corners where the suspension mounts? And, what specifically would you measure, how much lift it takes before you see it elsewhere in the car? I get what you are saying, just trying to be clear on how to check for it.
On another note, but also to do with chassis bracing/stifness, what about seam welding all of the unibody rails to the floorpan? Worthwhile or no?
Concerning the welding the floor pan to the unibody rails, what about re-inforcing the steering box mount? That is an issue many 3rd genners have and could probably make the steering better or less prone to breakage.
__________________ "An engine is like an orchestra. It's made up of wind, brass, percussion, and a whole range of other complimentary sections, all working to make that beautiful music that we call 'performance'..."
Steering box brace OR "Wonderbar"
It is a little spreader bar setup GM actually engineered as a baidaid fix to the factory cars fitted with wider tires. Wider tires meant more force exerted through the linkage to turn them...hich in turn meant in reverse fashion that the steering box was forced against the subrame railsflexing tthem and thus eventually cracking the box from the subframe. The Wonderbar braces the frame rails from flexing and eventually cracking.
It works pretty good, but in my opinion needs more help the higher the lateral grip and higher the turning force climbs. What did I do further? Well, I had the lucury of LOTS of room in the engine bay of a 60*V6 where all of the engine sits behind the centerline from spindle to spindle. I had room for a lateral brace behind the steering box attached to the subframe.
IMPORTANT NOTE 1) You can not do this the same way on a V8 car- motor extends too far foreward.
IMPORTANT NOTE 2) This again like the RAB has to be removable so it was made with swivel ends and preloaded OUTWARD just to put tension on the sibframe to prevent flesing in or out. Why outward? That has room for debate- Some will argue that the front of the A-arms should preload inward, but that is lower on the K-member which will NOT flex inward or outward under brakingor lateral load. this brace is merely for the steering box. The strut towers are also adjacent to the subframe here and they need to be kept spread for the camber, so I, figure why pull this inward. Preload it outward. Just keep solid tension on the steering box rail so it does not flex.
Result? My car had steering imputs like a damn jetfighter! I had 4 front lateral braces
1) 3pt STB
2) RSB (this Rear Steering box Brace)
3) RAB
4) Wonderbar (which I installed and tack welded ridgid so the bolts would not slip and loosen possibly- if I ever needed to remove it I could simply grind off the tack welds)
Vetruck. Wow, and I thought I had a good bead on suspension!! For some reason (subject matter, writing style, or I'm less tired) part 2 seemed to make more sense/more relevant than part 1. Not a knock, just maybe the difference between largely theoretical vs practical. Thank you for putting all this together, as I think I took out 2 things that are immediately applicable to my car, then I have a question that should be general enough to help the audience.
I have recently (in car's miles, not time) put on the LS1 front brake kit (from Ed Miller, I think his screen name is ebMiller), then swapped in an LS1 and T56 (originally L98/700R4). Since I have been driving it a lot in the last 1-2 months, I have noticed that the car wanders a LOT, has very poor habits when it comes to following 'truck ruts' etc. For example, level road with straight and curvy bits, it will go where I want it to just fine. As soon as the road becomes uneven (undulating as opposed to bumpy) it will try and change lanes, go from one side of the lane to the other, necessitating large corrections in steering from me to keep going in the intended direction/lane. From what I was able to glean from what was posted, this is possibly (probably?) due to scrub radius? - Note, at this point I have my doubts that the alignment is any good.. Also from what I understand from this post, I will need to use the Intrax "camber kit" to help eliminate this problem. I can do the alignment myself, so the attention to detail has 1 less layer of communication to get messed up in
Second thing I took from this is I may end up keeping my stock k-member. I don't think I had ever read/heard about the K-member bracing the front control arms, though it makes perfect sense. I was wondering why you had left that out from part 1, even though you had referenced spohn's a-arms. I had been on the verge of ordering the whole set up. Or at least saving up for it.
Last thing, using my car as an example, though I'm sure there are plenty out others out there in a similar position, what would be your order of operations for updating/upgrading the suspension/chassis? Here is what I think I'm understanding:
Chassis-
STB (3pt)
SFC
(already have the 'Wonder Bar)
Rear A-arm brace
Suspension-
New struts/shocks (current ones worn)
2" drop spindles (hadn't heard of these for 3rd gens until now)
Intrax "camber kit"
tuning
Sorry if I rambled, or if this should go in it's own thread, bit tired right now. Some of this is new stuff to me and I'm trying to make sure I am understanding things right. Any suggestions would be great for quality struts, but I realize that is a more preference thing, so I left it out. Would you mind PMing me? Again thanks for the info, always nice to find someone who knows what they are talking about.
If your front ride height changed, your camber and toe are likely off. Caster will also change slightly, but assuming that the nose went up that would add a little more positive caster and tend to make the car more directionally stable rather than less so.
That makes a lot of sense, and looking at the tire wear would support that with feathering on the shoulders starting to appear. With the drop spindles, the suspension settings won't change much, will they, like if lowering springs were used? So in effect, dropping so much weight from the nose made the camber situation worse, as I think, the settings are almost maxed out already judging by where the bolts are on the strut tower.
Good point and something more to think about for the guys doing LS1 swaps.
