Suns_PSD

My car handles great, I am installing some slightly shorter front tires and to keep the rake the same I thought I would raise the front of the car to offset the new smaller radius tires.

But then it occurred to me, is there a certain ideal rake, height, or some other measurement that I am not taking in to account? Maybe suspension geometry considerations?

I will not have any appreciable testing time as I only get to the track 1-3x/ year and I work insane hours, so I need to make the best decision, in the garage ahead of time.

Can anyone give me some guidance on this issue? Currently the car is pretty slammed btw.

Thanks!

96CollectorSport

Get yourself a trim height tool - this measures A-arm angle to let you know that your suspension is set-up properly.

I believe the J-tool number is J-42854 around $100 on Ebay.

ddahlgren

You mentioned how much smaller a tire. If you adjust the ride height to compensate for tire size the suspension geometry has to change.

Bill Dearborn

What is the difference in diameter of the tires? Make sure you are only looking at half that measurement since that is all the ride height changes. If you are talking a half inch or less I wouldn't worry about it.

Bill

Suns_PSD

11mm radius difference. Honestly some of the issue is the darn car is so low currently.

Trim height tool huh? I don't know what that is but I will look in to it.

Suns_PSD

Why all the complexity to measure A-Arm angle? I can do that with my cell phone. The important issue is what angle should the A-arm be set at for optimum performance? Hopefully there is a range?

Please advise.

96CollectorSport

Check out post #32 in the thread linked below:

https://www.corvetteforum.com/forums...pension-2.html

There are trim height specs in the service manual and I believe Pfadt had/has some specs as well.

Suns_PSD

Very useful. Thank you.

ddahlgren

If it handled well before and the tire radius is 11mm less just measure under the frame at the wheel centerline and raise it 11 mm.

Suns_PSD

I agree, that's what I have decided to do. I figure it can only improve my suspension anyways.

db2xpert

The Pfadt specs are for the fender height -- not accurate.
My left/right rear are off more than 1/2" when ride heights are set at the arms.

Nokones

Don't worry about the rake. It is more important to set the ride height and the cross weight to 50%. In order to have a good handling car the cross weight needs to be 50%. If the car looks lopsided, don't worry about the static attitude if the cross is 50%. When you put the car on the scales, make sure the scale pads are bubble or laser level, the tire pressures are set, the running fuel level is in the tank, driver's weight is appropriately set in the driver's seat, the swaybar(s) is/are disconnected, check and recheck by joucing the car when any adjustment is made. Then you drive the car around the block and put the car back on the scales and adjust to 50% cross.

Unless you add some weight to the car, good luck in trying to get the driver's side percentage better than 51%. You may get lucky in getting the front to rear 49/51 or even a little closer to 50/50. Don't sacrifice the cross for the front/rear or the side to side.

I hope this helps.

Suns_PSD

It does. My car is corner balanced and that's one of the things I'm concerned I'll mess up.

Does altering the rake, move the A-Arms and therefore effect your camber?

Thanks

96CollectorSport

The Pfadt chart I was referring to has three different locations to measure from - the fenders, the J-tool method and to the frame rail.
See attached pdf page 5.

http://www.pfadtracing.com/pdfs/Feat...2003.20.13.pdf

I find measuring with the J-tool is best for me - YMMV