trailing arm mounting locations IRS c4 corvette

[F1Fever]

I'm curious about the mounting points on an IRS C4 rear suspension.

I found some new brackets that claim they spread the mounting points on the chassis to gain traction. i was under the impression that the lower control arm to chassis would need to be moved upward to increase the forward bite?

for those not familiar here is a pic:

Precise weight transfer is critical for optimum acceleration, braking and cornering. DRM brackets alter the trailing arm mounting point locations taking some of the anti-squat out of the Corvette. The additional weight transfer results in improved traction. Improvement will be realized at autocross, road course and drag racing events.

We spread out the holes on the trailing arm brackets which reduces the anti squat. That helps the car transfer the weight to the rear tires

Now I'm not one to just buy parts (and prefer to make or modify), I want to know how and why they work. These are conflicting with how I understand traction to work. So really my question is... is my thinking right tht I should be raising the lower trailing arm to chassis mounting point or are they correct and it should be lowered??

[af2]

Look at the IC then you will be able to see the difference.

[F1Fever]

I did find this:


but can you elaborate, for some reason I'm having a hard time understanding anything with this IRS except anti-dive and anti-squat, and maybe not even that.

I can see how the brakes would cause a rotating of the spindle on braking but on acceleration all I can see in my head is the spindle pushing forward against the control arms. In the picture above the axle centerline is below each chassis mounting point, and this should result in greater than 100% anti-squat. I do not see how lowering the lower control arm chassis point will increase straight line traction (I do however see how raising the upper mounting point will).

I really need a lesson here, but I'm reading contradicting things in different places, one person that does not agree with another etc.


I understand engines, so when I read "LCA" I'm thinking camshaft...

[af2]

Some good reading from a retired automotive engineer.

http://www.racetec.cc/shope/

[mbrooks]

i don't think it's going to matter. the cg moves rearward on acceleration, the top of the shock mount is higher then the cg, the 4 link is going to lock up, you will have no weight transfer acting through the suspension, what's there is there.

the links are so short any suspension movement in cornering is going to induce lots of toe steer.

but this is all speculation.

i would put the lower arms at level unless you are looking for some type of toe steer, the top link should be angled down approx. 7-10 deg on a three link setup if i remember correctly. but like i said, don't think it will matter on this setup.

for the 4 link, the links should be parallel if you want your suspension to move at all.

i've read somewhere, can't remember who said it though, you can make any suspension work by not letting it.

[F1Fever]

I lowered the car 1 inch in the rear from the above image.
I think this brought the upper control arms mounting point close to equal with the CG and the lower control arms chassis mounting point just below the axle centerline.

I have lost all forward bite by doing this, yet was hoping to be able to further reduce the rear by 3/4" of an inch.

I am skeptical that the brackets above will fix the issue. I am thinking that I should either raise either the lower control arm chassis mounting point or both. and maybe shoot for 130% anti-squat?
\

ladder bars are so simple in comparison

i've read somewhere, can't remember who said it though, you can make any suspension work by not letting it.

I've heard/read that before myself...

[RCJ]

If I'm looking at your drawing correctly you are showing the center of gravity at 96.2 from the rear axle.This does not seem right for a vette or match the scale of your drawing.By changing the front mounting points I would guess they are putting the IC in front of the CG trying to get the nose to rise more.This raises the CG and transfers more weight to the rear.

[F1Fever]

That is actually a drawing somebody else did, I just posted it here. the 96.2" is the wheelbase. 15" is the generally accepted CG for this car from what I can find, others say 18"
The thread where that was posted to was OK but it didn't really answer my question.

http://forums.corvetteforum.com/autocro ... -much.html

[RCJ]

Because of the lower CG ,stiff springs, high rebound shocks,not alot of weight behind the axle, the main factor in how much traction you produce is to get the weight to transfer to the rear.On a car with high CG, soft springs, that doesn't have any problems with weight transfer to the rear, anti squat gives some added bite and quick transfer to the tire at the first hit of the throttle.After the first hit the weight transfer keeps the tires stuck.
When you lowered your car you lowered the center of gravity.Here is the equation for weight transfer,(G-force)(weight)(cg height)divided by(wheelbase)