Supercharged111

Last year I lowered my car on stock bolts.

http://forums.corvetteforum.com/auto...it-faster.html

Of the front 2 that took the fewest turns, I matched the 3 other corners to it. Only way to get better would be corner balance with adjustable swaybar endlinks. The rear fender gap is quite noticeable, the front actually looks really good. I decided to revisit and see if the rake angle needed tweaking so I measured ride height at the frame rail where jacking pucks screw in and found it to be level, not 1/2"+ higher out back like I thought I'd see. I realize that an actual 1/2" difference wouldn't read as high from where I measured. Front fender height is 27", rear is 28", and yet the car sits level? I know I'm supposed to have a slight rake to prevent lift but I don't and it looks like I do. . .

trackboss

I measure at the lower control arm pickup points. The frame is not a great place to measure. There are several reasons, but one is that a small change in the height at the frame near the tie down points is a much bigger change at the suspension points where it actually matters(front to back).
As far as the rake just try raising/lowering the rear only at the track between sessions and see what it does. Equal turns both sides and take notes. Actual performance is what really matters.

Supercharged111

Hmm, right at the bolts themselves? That's not a bad idea. But how do you get good results with all the anti squat and anti dive built into those pickup points?

froggy47

Is there a way to get to those points with whells on & on the ground? I always knew that's the right way to do it but practically speaking could not figure a way.

I always set 1/4 inch at the frame points & that translates to ???XXX at the suspension points. Any one ever calculate that ?

Or in reverse if you have 1/2 inch at the suspension points what do you get at the tie downs?

trackboss

the geometry is fixed and doesn't matter for what you are doing. Pick a single spot at each corner and use it consistently. The rear lower control arm bolts are the easiest to get to laying on the ground. It doesn't have to be the bolt itself. You can go up to the cross member just below the bolt.
Froggy, some math will get you the answers you are looking for, but why make it so complicated? The frame may not be perfectly straight anyway. Or there may be something as simple as a dimple in the frame from jacking it up which will throw off the results. Measure from the lca bolt area does not have that problem.
In any case the car needs to be on a level plane and the suspension unbound to get consistent results.

Apocolipse

Is it the aero effects of the rake that makes the difference or is it the roll axis angle front to rear that's making the handling difference.

Supercharged111

That's a real good question. I've always been under the impression that it's for aero because I'm not trying to alter the factory rake which I assume has taken roll axis inclination into consideration.

Miguel S

I asked this question in another thread and I concluded that without additional aero to offer stability, you need to keep the rake regardless of the suspension geometry hit. My question was if you were to run a square setup, would the roll axis inclination change for the worse since the rear of the car would no longer be at the same height relative to its "sweet spot". Basically you would set the front of the car to the sweet spot, but setting the rear for the correct rake wouldn't be the same as with the stock tires. But I suppose till I put on real bushings/bearings, my suspension is all over the place anyway. Just in here to learn and nerd out.

Apocolipse

Well, considering race teams who run square seem to kick our *** around a track leads me to believe that the 1/2" difference in axis angle f/r is not a big deal compared to the handling benefits of going square.

Do they tend to increase rake vs stock?