I just got new tires and a 4 wheel alignment done. The car pulls slightly to the right now.

It tracked perfectly straight with the old Goodyears.

2002 C5 convertible. Michelin Pilot A/S Sports Plus tires

The alignment setting are:

Front
Caster Left 7.3
Right 7.8
the caster on the old GYs are 7.6 on both left/right front.

Camber Left -0.5
Right -0.5

Toe Left 1/16"
Right 1/16"
Total 1/8"

Rear
Camber Left -0.2
Right -0.2

Toe Left 1/16"
Right 1/16"
Total 1/8"

The tech told me that the spread between the left and right caster on the the front wheels is to counter the Michelin's tendency to pull right.

Since there is still a small pull, I am taking it in again to the shop.

Is it OK to increase the caster spread? Increase right some more OR decrease left?

Any one else experienced the right pull?

Or is something wrong with the tires and I should have them replaced.

Tirerack said to swap the right and left tires and see if there is a left pull. If yes, then the tires are bad. Should I bother with that? Or just adjust the caster.

Thanks for any advice.
Ankur

 

I think you have a little too much cross caster - should be less than .5 degree difference between left and right. You're right at the .5 difference now.

 

What would be the best way to proceed? Appreciate any insights...

 

I would take it back to the alignment shop and tell them the alignment is unsatisfactory - pulling the car to the right due to excessive cross caster. Need to either increase the left caster by .2 or .3, or reduce the right caster by .2 or .3. They should be able to show you a C5 or C5/Z06 alignment specs - depending on what you chose - on their alignment machine (print out) and compare your final results to those OEM specs.

Stock GM alignment specs for C5 Z06:

Front Individual Toe: +0.04 degree +/- 0.10 degree

Front Sum Toe: +0.08 degree +/- 0.20 degree

Front Individual Caster: +6.9 degree +/- 0.50 degree

Front Cross Caster: within +/- 0.25 degree

Front Individual Camber: -0.70 degree +/-0.50 degree

Front Cross Camber: within +/-0.25 degree

Rear Individual Toe: -0.01 degree +/- 0.10 degree

Rear Sum Toe: -0.02 degree +/- 0.20 degree

Rear Individual Camber: -0.68 degree +/- 0.50 degree

Rear Cross Camber: within +/- 0.50 degree

 

It's ok to change the caster a bit to compensate for a pull...don't forget that most roads have a crown and therefore the car will always pull a bit right on most roads. Some shops will set the caster to compensate for this pull so that the car tracks straight on most roads...good luck.

 

 

caster does not wear tires, and cross caster can be adjusted to make the car go straight....

 

Thanks for all the replies...

A newbie clarification:

Front
Caster Left 7.3
Right 7.8

Is this spread too much and is causing the car to go right? Is that what you would call excessive cross caster and they should reduce it to say: 7.5 and 7.7? The old GY settings were 7.6 on both sides and it went straight.

Or, the spread was put to counter the crown and it's still not enough. This is the impression I got from the tech. If that's the case, and the shop says they will increase it (which folks above say is a No-No) then , should I say No, have them revert it to 7.6 on both wheels and contact Tirerack and tell them the tire is bad? If so, which tire?

Thanks for helping me resolve this one...

 

Caster:

The caster angle identifies the forward or backward slope of a line drawn through the upper and lower steering pivot points when viewed directly from the side of the vehicle. Caster is expressed in degrees and is measured by comparing a line running through the steering system's upper and lower pivot points (typically the upper and lower ball joints of an A-arm or wishbone suspension design, or the lower ball joint and the strut tower mount of a McPherson strut design) to a line drawn perpendicular to the ground. Caster is said to be positive if the line slopes towards the rear of the vehicle at the top, and negative if the line slopes towards the front.



Caster angle settings allow the vehicle manufacturer to balance steering effort, high speed stability and front end cornering effectiveness.

Increasing the amount of positive caster will increase steering effort and straight line tracking, as well as improve high speed stability and cornering effectiveness. Positive caster also increases tire lean when cornering (almost like having more negative camber) as the steering angle is increased.

The effects of positive caster are pretty much "positive," especially increasing the lean of the tire when the vehicle is cornering while returning it to a more upright position when driving straight ahead.

Cross-Camber and Cross-Caster:

Most street car alignments call for the front camber and caster settings to be adjusted to slightly different specifications on the right side of the vehicle compared to the left side. These slight side-to-side differences are called cross-camber and cross-caster.

For vehicles set up to drive on the "right" side of the road, the right side is aligned with a little more negative camber (about .25 degrees) and a little more positive caster (again, about .25 degrees) to help the vehicle resist the influence of crowned roads that would cause it to drift "downhill" to the right gutter. Since most roads are crowned, cross-camber and cross-caster are helpful the majority of the time, however they will cause a vehicle to drift to the left on a perfectly flat road or a road that leans to the left.