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And I have done my own alignments for 45 years, on street and solo cars.
The most important spec is rear toe-in, you need 1/8" or it will get very squirrelly, not more because it will wear tires.
Push the caster well past the GM 1-2* pos if the car allows it, 3 or 4* may be available with stock parts, and it will be calmer in a straight line. The more the better. With some aftermarket bits you can get 4 or 5* which is even better. Better road feel also. But it will get heavier if you have manual steering, so if you do proceed cautiously.
You may have to give these specs to an alignment shop and convince them to use them. Just tell them the old GM specs are for old bias-ply tires, and these are for radials, and that should do it.
The second chart has toe-in in degrees (vs inches) which is what 90% of the alignment machines use these days.
The most important spec is FRONT toe-in (1/16" - 3/32"). Rears should be dead-nuts straight, if possible, to keep from wearing the edges of the tires. You will get a bit of 'scrubbing' on the fronts due to light toe-in, but that keeps the front from wandering around. Do regular tire rotations about every 5K miles to even the tire wear.
There is not that much difference between 1/32" and zero front toe.
But at 3/32" you could definately cut it down.
Would you feel it?
I don't know. I could.
But I raced with many alignment settings for many years and learned what felt like what.
3/32" will give you more tire drag than necessary. It will deaden the steering on-center just a little bit. It will take a little more of a turn of the steering wheel before the car responds.
Zero toe is the opposite. The most likely thing you may notice is it turns a little quicker, just a little faster, when you first touch the wheel.
But if you have any slack in your steering system you may not feel the difference.
3/32" will wear the tires faster. It is important when you are trying to get 60k miles out of a set of expensive Michilens.
Is it important on a car that likely gets lower miles put on it?
Even I would not pay to have it re-done, on most c3s, not just for that.
But if you can do your own, and want to see if you can feel the difference, go for it!
IMHO The most important setting is the rear toe-in.
Notice that all of Van-Steels rear toe-in settings are 1/8" toe-in. Even more for the race version.
Seems like a lot when we can run the front at zero toe right?
It is because of the old school 3 link rear IRS, where newer designs run 4 or 5 links on each side.
Ours moves towards toe-out when the car turns and rolls.
The 1/8" static toe-in setting keeps it from going past zero and into toe-out, hopefully, in a turn.
If it hits toe-out in a turn, it will feel like someone grabbed the rear end and pulled it to the outside of the turn.
Then you let off, the car un-rolls, and it goes away.
It is a very un-nerving feeling to have the rear steer itself, and un-steer in mid-corner.
I hope none of you ever experience it.
It is called bump-steer.
Some C2/C3 race cars run 2-1/2 times that much rear toe-in to keep the rear under control.
Deteriorated rear trailing arm front bushings will also cause the exact same effect, perhaps even worse.
I know they are very hard to check, but if your car suddenly develops a "squirrelly" feel, that is one likely cause.
A typical hard turn in a stock corvette will have 1.5-2.0" of bump travel or compression in the outside rear wheel.
This will generate .180" of bump-steer, or toe-out.
If you start with half of your total toe, or -1/16" or .060" of toe-in, on each side of the car, and then add +.180" of toe-out, due to "bump", you wind up with + 0.120" of toe-out in the outside rear tire, (+1/8" out). And also -.060 -.270 = -.330" of toe-in in the inside rear tire, which is also pointing to the outside of the turn. So both rear tires are trying to steer to the outside of the turn. Now the total rear toe-in is +.120-.330 = -.210" It just changed from -1/8" to almost -1/4" toe-in, but it is not straight anymore, it is trying to steer left.
The absolute best thing you can do, and almost the only thing you can do, to cut out the twitchiness, is to cut down the amount of roll, by adding stiffer anti-sway bars, and cut the roll, and the rear bump steer, in half.
Last edited by leigh1322; Apr 29, 2025 at 10:15 PM.
When Bridgehampton was still around, I found the toe settings made a huge difference. Toe out was a disaster. The car wandered all over the place. Zero toe was better, but toe in was best. Replacing the rubber trailing arm bushings with steel helped too. Darn, I miss Guldstrand.
He did a very good job to the book spec.
Middle of the spec on everything and nice and even both sides.
But that is a lot of toe-in.
Bias tires or radials?
Manual steer or power?
That much toe-in will wear tires but make it stable.
Looks like old GM specs for bias tires.
It should drive great though.
Nice LT-1 in a great color Steel City Grey I think?
It is the front toe that could go down, way down.
.54* = 1/4" front toe in. Wow!
But that is the old GM service spec.
With radials more ideal would be 1/32" or .031" or .07*
That is 8 times less front toe-in than he has now!
But that low value is not even loaded into the machine.
The machine says the minimum is .25* degrees.
I am pretty sure those are the old GM factory bias ply tire specs.
So if you do not print out and show them the Van Steel spec sheet, you get what GM said, 50 years ago, for bias ply tires.
From GM chassis service manual:
GM was OK with a wide range of toe-in in those days. But bias tires wore out pretty fast, so it did not really matter. 1/8 to 1/16" was still OK. With modern expensive high performance radials, 1/32" is more the norm, for maximum life. Old bias tires might last 10k miles. Modern radials can go 80k.
But would it drive differently? Not really. It is mostly about tire wear.
Last edited by leigh1322; May 4, 2025 at 02:48 PM.
He did a very good job to the book spec.
Middle of the spec on everything and nice and even both sides.
But that is a lot of toe-in.
Bias tires or radials?
Manual steer or power?
That much toe-in will wear tires but make it stable.
Looks like old GM specs for bias tires.
It should drive great though.
Nice LT-1 in a great color Steel City Grey I think?
Yes 72 LT-1 coupe. Steel cities gray black guts. Manual steering freshly rebuilt by Bairs. New 225/70-15 BF Goodrich TAs at 30psi. Not too worried about wear as the tires will age out before wear out.
Car does drive great. Only had it up to 90 MPH so far but was very stable.
This winter I plan on rebuilding the front suspension so it will need to be aligned again. On the next go round I may ask him to lighten up a bit on the tow and add more caster.
Do you know why GM would spec 3 different alignment scenarios that are quite different from each other?
not sure but my guess would be..
#1- decides if warranty or paid service should be done .. go no go..
#2- assume a range to say at inspection (not sure who's inspection) to allow to be driven or needs attention now.
#3- as designed new car.. recommended. I use this one for alignment guy. assume radials out for a while in 79.
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