Just you give you an idea of how much toe changes when you adjust your camber.

orig spec.

camber = -0.3 degree's
total toe = 1/16" toe in.
Caster + 3.7 degree's


New spec

camber = -1.6 degree's
total toe = 15/32" toe out.
caster = + 4.0 degree's

This is the change I get when I setup for track days. This was before I changed the toe back to my desired spec.

Today I decided to see how much it actually changes.

 

Are you saying that if I add an equal amount of shim to the fore and aft control arm mount bolts to cause the top of he wheel to tilt further inboard, it affects caster and toe? I thought camber was the only thing I could change without affecting the other geometry. Can you explain how that happens?

 

Frame must be bent

 

For a rear steer type vehicle I would expect toe to go IN when adjusting more negative camber. Since the tie rod is in the rear of the knuckle the front of the tie will turn in with the top of the tire going in.

Think about it this way, the tire is essentially held in place by 3 points. Upper control arm on the top, lower control arm on the bottom, and the tie rod on the back side. As you tilt the top of the tire in for more negative camber, the length of the tie rod on the one side does not change so the tire basically rotates in a little. For newer Corvettes where the tie rod is in the front of the tire (known as front steer) the opposite happens. As you tilt the top of the tire in the rear of the tire rotates in and creates toe OUT. You should always adjust camber/caster together and then finish up with toe.

 

A perfectly thought out answer. It just goes to show that you can't beat logic.

 

OK, I'll buy that but the example detailed in the original post had the opposite result, if I'm understanding correctly. Toe-in should have increased with the increase in negative camber, not gone to a toe-out condition.
So how is it that the camber change would affect caster?

 

That was the point I was arguing. Unless he measures toe differently for some reason, it should have more toe IN.

Even if you use the same amount of shims on each bolt there are manufacturing tolerances in the shims and when they stack up can most certainly move caster. Sometimes you have to mess around with different shims or use another thickness all together.

 

In my head....using three points of reference....it should have more toe in......

Jebby

 

SAI and included angle need to be accounted for . that is part of the reason camber changes effect caster.

 

what is SAI and included angle?

 

SAI ( steering axis inclination) is the angle between the upper and lower ball joint , the included angle is when you add the SAI and camber together. SAI is also known as KPI ( King Pin Inclination) at least it was back in the stone age when i was involved with alignment studies . camber roll in turns is the visible effect of SAI. SAI also has a big impact on wheel offset and greatly effects scrub radius.

 

When I am done with the track day event and return the camber to street settings. I will measure the before and after again.

 

This thread is a nice contribution to alignment questions. I am curious as to whether you have incorporated bump steer correction in your front end setup?

 

Stock setup except for SPC Upper control arms and poly bushings in stock lower control arms. 550# vbandp front springs.

 

I have just returned the front to street specs.

Before

-1.3 Degree's Camber
1/32" toe in
Caster 3.8 degree's

After

-0.1 Degree's Camber
12/32" toe in
Caster 4.0 degree's

What I find interesting is the caster change.

And here is why.

Original setup I added negative camber and got 3 degree's more positive caster.

Then I corrected toe in since the camber change added more toe out. (never re-checked caster) but based on the before measurements compared to the after when I added more toe in, the caster looks to have changed from 3.7 to 3.8 or in-fact be the same (+- 0.1). I lost caster adding more toe in)

Then after the track event I removed negative camber got more toe in, but also got more caster.

I am going to check the adjustment of toe changes affecting caster.

My understanding it shouldn't but ? It my have something to do with how the camber caster gauge works. It isn't really measuring the true caster angle but calculate it based on camber changes with the wheel Turing 30 degree's and divide the difference by 1.5

Anyway this is the results I got returning the camber back to street specs.

I am going to return the toe next and see what happens.