Suspension Dynamics

[GTS Dean]

#593664

Because of short/long arm wishbones, your car will increase negative camber with compression. Depending on how your inner toe links are set for height, toe can change from zero to a whole lot through the travel range.

[pokeyl]

#593666

Yes I just went up on rear ride hight due to front tire size change (rake). Now with my gauge I have Zero rear camber. I’ll jack it later and add it back.
Also found I am out (difference).2 degrees (Left to right) rear caster. I have the kit and DRB. I’ll set the toe last

[GTS Dean]

#593676

0.2 is not bad at all. But if you have the DRB, then less is better.

[pokeyl]

#593677

Anyone that can set the caster without a DRBIII is a god! I can’t imagine setting the caster/camber without the real time readout.
DRB did lock up one time, don’t know why, reboot cleared it.
Just finished, toe is 3/16, IN. Thought raising the suspension would cause it to move out, that long with increasing camber, well back to 1.3.
Will drive it tomorrow see who it feels.

Thanks Dean, learned a lot today.

[pokeyl]

#593692

Played around with the rear adj this morning. found is you need to add or remove camber, take 1/2 from each adjuster and the caster stays SPOT ON.

Still have to reset toe, easy!

[Pappy]

#593711

GTS Dean said:
Because of short/long arm wishbones, your car will increase negative camber with compression. Depending on how your inner toe links are set for height, toe can change from zero to a whole lot through the travel range.

There can be a lot to this. Depending on, believe it or not, the anti-dive angle of the control arms can determine whether or not you get camber change with compression. There is a long explanation for that. However, one thing that does change with compression is caster, and that’s a good thing. The caster change in itself doesn’t change camber, BUT when you turn the wheels you get significantly increased negative camber on the outside tire (in a turn) and decreased (usually becoming positive) camber on the inside tire. That is a good thing. That is the reason I set up my track car (non-Viper) with zero camber gain with compression (keeps the wheels flatter on the ground for straight-ahead braking),but I use a lot of caster gain (caster up to 10+ degrees at full compression) to get the most “good” camber gain when the wheels are turned.

Pappy

[TKO MOTORSPORTS TEAM]

#593787

Pappy said:
There can be a lot to this. Depending on, believe it or not, the anti-dive angle of the control arms can determine whether or not you get camber change with compression. There is a long explanation for that. However, one thing that does change with compression is caster, and that's a good thing. The caster change in itself doesn't change camber, BUT when you turn the wheels you get significantly increased negative camber on the outside tire (in a turn) and decreased (usually becoming positive) camber on the inside tire. That is a good thing. That is the reason I set up my track car (non-Viper) with zero camber gain with compression (keeps the wheels flatter on the ground for straight-ahead braking),but I use a lot of caster gain (caster up to 10+ degrees at full compression) to get the most "good" camber gain when the wheels are turned.

Pappy

this is kinda of correct Pappy.

[pokeyl]

#593792

I guess I’ll jack it, remove the coil over and sway bar link, and map it, front and rear.
Build a 3D model and then I can use data capture (body pitch, roll, shock compression) and see what works best for me.

Thanks for all the input.

[pokeyl]

#594306

Last Question, front scrub radius, Gen 3? We are in the bonus round questions now!

[TKO MOTORSPORTS TEAM]

#594316

pokeyl said:
Last Question, front scrub radius, Gen 3? We are in the bonus round questions now!

If your going to change or try and improve the scrub radius zero or slightly positive if you can is always a good bet with a front engine car with moderate aero. Vipers scrub radius is a especially important because of known front tire wear probelms. The factory has a done a decent job but there is always room for improvement for your specific application.

[TKO MOTORSPORTS TEAM]

#594317

pokeyl said:
Last Question, front scrub radius, Gen 3? We are in the bonus round questions now!

Just curious. What are you trying to achieve?

[pokeyl]

#594334

I went up to a taller/wider tire 305/30-19 on the front with CF5V Forge Star wheels 19×11. ET 43mm. Car darts, follows road ruts bad. I have the same F14 wheels with the same tire in 285/30-19. That .7 inch smaller radius and its fine. I my search for more front grip I have upset the scrub radius BAD! I tried adding some additional tow in and caster. Next will be more camber. Learning a lot about a great many thing. Thanks for all the help. Everyone!!!

[TKO MOTORSPORTS TEAM]

#594340

pokeyl said:
I went up to a taller/wider tire 305/30-19 on the front with CF5V Forge Star wheels 19×11. ET 43mm. Car darts, follows road ruts bad. I have the same F14 wheels with the same tire in 285/30-19. That .7 inch smaller radius and its fine. I my search for more front grip I have upset the scrub radius BAD! I tried adding some additional tow in and caster. Next will be more camber. Learning a lot about a great many thing. Thanks for all the help. Everyone!!!

With what your explaining “Car darts, follows road ruts bad” and you went to taller wider tire is more then likely a tire problem if everything else in your set up checks out or is with in the norm. Different tire construction ,side wall stiffness, width and with street tires tread design can cause some very strange stability problems. Unfortunately tire and wheel combos are a learn as you go type deal. Change in scrub radius due to wheels could amplify the problem but its not the major cause of the car darting and following ruts. There are also alot of things inboard of the tire that can also affect the dynamics of the car. The driver aids also have a tendency to do some very strange things if you go beyond +4% of factory tire diameter.

[Shannon Whitehead]

#594348

It looks like you have a Gen 3 car with a rear wing and small front splitter, which requires a special setup, but it really depends on the use of the car.

Rear caster are toe need to be right, or the handling is dangerous. Lowering the car means you need to check the bump steer, which is very time consuming.

Don’t make too many changes in the rear of the car unless you have a proper system to check it.

[pokeyl]

#594354

Yes to all above, I have the DRBIII and caster test kit, tow plates, string (working on a set of weight plates). I may end up doing the full bump steer teat as listed. For right now I’ll go back to my ACR tires. they track perfect.

[TKO MOTORSPORTS TEAM]

#594390

pokeyl said:
Yes to all above, I have the DRBIII and caster test kit, tow plates, string (working on a set of weight plates). I may end up doing the full bump steer teat as listed. For right now I'll go back to my ACR tires. they track perfect.

Bump-steer is relatively easy todo with the proper tool and you always want zero or as close to zero as possible through total shock travel not total suspension travel. Do the bump-steer check after you have set caster; caster will aways change your SAI to a small degree. ( max 7 deg caster with stock or TKO control arm bushings). Set static camber and your toe. Most vipers stock you will see .060-.125″ total bump-steer. To correct the bump-steer you will need to convert to spherical bearing tie rod ends and an outside chance shim the rack. Rear is the same zero bump is best option and caster keep it to absolute minimum.

Here is the pissing up stream part of the entire exercise. Vipers do not hold a setup for shit; If your using your viper on track or having fun. The eccentric adjusters are so overloaded one good bump under load and out goes your setup. Camber caster lock out plates are the only way to correct this problem if your run factory or TKO bushings. If your running spherical bearings in the control arms then a shim kit will also work.

[pokeyl]

#594457

Todays test same, wheel, off-sets, Tow, Caster, Camber same 285/30-19 P-Zero…. tracks perfect! Todays tire is a P-Zero and not the P-zero Corsa.

.7 inch higher and 20mm wider causing a Massive Difference! Rake is higher!

[pokeyl]

#594560

Test this morning 80-90-100 total stable. I have a vibration I think a tire lost a weight.

[GTS Dean]

#594571

Corsas must have a different construction in the sidewall support insert, possibly the belt layout that makes it more nervous.

[pokeyl]

#594576

I drove the car with Corsas 295-30/18… 355-30/19… for a year, all good.
It has to be the tire hight, or bad tires!!! How do I prove that to Tire Rack?

[Shannon Whitehead]

#594577

I have Corsas on two Vipers and no issue for street driving at all. The issues I have experienced include tire stutter during slow max turns with cold tires and losing grip and chunking on the track when hot.

[13COBRA]

#594579

pokeyl said:
I drove the car with Corsas 295-30/18… 355-30/19… for a year, all good.
It has to be the tire hight, or bad tires!!! How do I prove that to Tire Rack?

You’d have to have it on a road test balancer and then it has to test outside of their specs and margin of error.

[pokeyl]

#594586

I’ll see if there is one in town. Thanks

13COBRA said:
You'd have to have it on a road test balancer and then it has to test outside of their specs and margin of error.

[Shannon Whitehead]

#39713

Anyone know If the Suspension adds tow/camber as you decrease ride night… IE downforce from Aero?

In a perfect world it would be no change. But I don’t live there!

Thanks in advance

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