Suspension fine tuning

So I did my first auto-x after changing a few things on the vette (larger/wider wheels, raised diff, and tall ball joint UCA's)
I was really impressed with how everything performed considering all of my spring rate, and alignment settings were either eyeballed or left the same from the previous setup.
Anyway, heres what I noticed...

Dual mount spring in the rear- Hardest spring setting. Loved it. Significantly less body roll (no rear sway) compared to the 3rd hardest setting. Did not change alignment other than raising the diff which probably reduced my (-) camber a bit.

Dual mount front spring with 1.125" sway and tall ball joint UCA's- 2nd softest spring setting- Low speed turns the car was pushing pretty bad unless I gassed it to swing the rear around. Higher speed, it was the rear that would let out first. Last time I checked, I have 0 toe. Eyeballed camber, and castor settings :tomato: Tires were noticeably hotter(by hand) on the outside.

I actually really liked how the rear behaved (predictable and easy to control oversteer!) and I think I will leave that alone for now. But the front seems like it doesnt have enough (-) camber. This is a street car, so I dont want to run alot of static camber. Can the the high speed/low speed differences be tuned out or do I have to make a compromise? I have to find some time to get it on a real alignment rack to see where Im really at.

And to brag just a little... fastest time of the day was an instructor with 44.5 seconds in an S2000. I managed a 46.5 on my last run. Definitely brought my spirits up! :thankyou:

nice job.... excellent time!
I'm still struggling with chasing gremlins out of my car - don't think I'll make it before the season ends in rain. I've been driving my car a lot, and the rear springs are just too soft for the lowered suspension (constantly on the bumpstops).... but all of what you said makes me wonder if I'm going the wrong direction.... maybe I should have went with the same rear spring you have an said goodbye to the rear sway bar. I took mine off, but it is better with it on - but I have a soft, composite spring

you should really find a shop that can do a track spec alignment to your car instead of just eye balling it. a decent race shop will weight the car down correctly and either use your specs or rec. specs for the car. glad to see its running so good but i bet it would be faster onces its set up and you know the tires aren't fighting each other.

fastcompany2 said:

you should really find a shop that can do a track spec alignment to your car instead of just eye balling it. a decent race shop will weight the car down correctly and either use your specs or rec. specs for the car. glad to see its running so good but i bet it would be faster onces its set up and you know the tires aren't fighting each other.

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in addition to scaling the car, with the drivers weight in the seat and a half a tank of gas...

A very usefull thing is to have some friend taking a picture of your car when cornering very fast.
This will let you check how much roll you have (degrees).... front and rear and will tell you how much camber gain you will need at least.
Of course your roll angle will subtract from the camber angle at the wheel...... so 3° of body roll will ask for at least 3° of camber gain.
Now you can be the ballpark of the things..... but you still will have to check tire temperature outside, center and inside.

For the front camber problem I would like to try the maximum positive caster you can:
this will create some negative camber when steering (specially in auto-x with very tight corners) but will let you have the wheels well perpendicular to the ground when braking before the corner.

The downside is that the stock frontend of a Vette allows not more than 3° to 4° of positive caster.
Unless you will change at least the upper a-arm no way to have more.

A cheep solution is to relocate the two front holes where the lower a-arm shaft is bolted. Moving these holes towards the center of the car will allow for a lot more caster.

Remember that when braking the arm is moving towards the rear (due to the flex of the bushings) reducing the allready little caster...... this will make the car unpredictable when releasing the brakes because the suspension will suddenly restore the original caster (with the consequent camber) at the beginning of the corner.

This is only one of the reasons for replacing the rubber bushings with a more rigid solution (nylon, bras or rodends).

With the these infos you can check if the camber is correct and if the tires are at the correct pressure.

Another thing is to check the tire load at the four corners. Often people check if the fenders are at the same distance from the ground or if the frame is at the same distance frome the ground in the four corners...... but this is NOT correct.

You really need the same load (left- right).... not the same ride height !

The best way to do it is with wheel scales..... but there is a "el cheepo" way to do it:

Rise the rear of the car placing a strong round steel rod (some 1" OD) exactely in the middle of the rear crossmember in order to create a pivot point centered in the rear of the frame.
Then measure the distance beetween the FL and FR of the frame and the ground.
Then check if the distance are the sames with all wheel in the ground
If the measures are equal you are not far from a well balanced frontend.

Repeat the same procedure for the rearend.

Remember that the load will move allways diagonally, so to correct some discrepace you can operate in both front or rear wheels located in the diagonal.
This will let you to correct the load doing some ride eight adjustment.

Only my two cents....

I have four bags of sand to stack in my seat when doing setups.

And would you believe a puppy will chew the corners out of stacked bags of sand???:rofl:

I have a friend that works at a race car shop (actually ran a few C3 vettes out of there). Hes got scales and an alignment rack that I will use.
The reasoning for the eyeballed alignment was because it is a pain for me to get down to his shop, so I figured I would get some seat of the pants data before going down to get the alignment so I could get it as close as possible

Stroker-427 said:

For the front camber problem I would like to try the maximum positive caster you can:
this will create some negative camber when steering (specially in auto-x with very tight corners) but will let you have the wheels well perpendicular to the ground when braking before the corner.

Click to expand...

Ahh I did not think of this... excellent info :thumbs:
I have the SPC arms, so no difficulty in getting the desired castor... No power steering will limit how much I can tolerate on the street

SPC are excellent arms (I have it in my car) and ou can reach easly 6-7° of positive caster.

GT6Steve said:

I have four bags of sand to stack in my seat when doing setups.

And would you believe a puppy will chew the corners out of stacked bags of sand???:rofl:

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4 bags - 100# per bag, dang, do you get into your C3 like a large girl gets in skinny jeans (jumping from the 3rd story window) :huh:

and yes, I believe that ..... I have a bloodhound that is a tax deduction because of the damage she's done (she's a Search and Rescue dog, so she is a deduction)

and let me suggest another option for alignments

Had one of those and didn't really like it. I didn't trust the way it mounted on my little Britsh racer. I use the Mitchell device.

My bags were 55 Lbs each so it coincided nicely with my fat ass. Sadly the pup went the wrong way, or I did...

I still string the car off of known centerlines with good results



BTW, my Mitchell is autograghed by Wayne, a long time friend.

very nice.... I like my set up now that I have steel flat plates on the torque thrusts.... makes camber and caster resets pretty easy. But I hear you on not liking how they mount - if you read the instructions, I've better suggestions from bubba as to how to mount that.