Question for Alignment Experts

[CharlieBauer]

The first step in an alignment is to set the correct tire pressure.

If the pressure was set a few psi above or below the pressure the owner runs the tires at, would that affect the alignment in any way and if so, how and how much?

 

[Deleted member 89374]

The first step in an alignment is to set the correct tire pressure.

If the pressure was set a few psi above or below the pressure the owner runs the tires at, would that affect the alignment in any way and if so, how and how much?

No, it wouldn't because alignment machines don't work off the tire pressure to get accurate measurements.

 

[DuckRyder]

Assuming they are all equally off no affect.

 

[atikovi]

It's called a WHEEL alignment, not a TIRE alignment.

 

[slo town]

Assuming they are all equally off no affect.

The best answer so far.

It's called a WHEEL alignment, not a TIRE alignment.

So you're saying that if I set the left front to 32 psi and the right front to 12 psi that will not affect the alignment? At a minimum it's going to cause the camber to be set incorrectly.

Scott

 

[atikovi]

So you're saying that if I set the left front to 32 psi and the right front to 12 psi that will not affect the alignment?

No, I'm not saying that.

 

[slo town]

No, I'm not saying that.

I didn't think so, but I think you should have offered more clarity in your comment.

Let's suppose I run the fronts to spec and the rears to 25 psi lower than spec. This would prevent a proper alignment from being achieved even though the side-to-side differences were the same. For example, if I run the rears at 10 psi and the fronts to spec, the front end caster would be off because the rear end of the car was too low.

OP, if you want to tweak ride or handling characteristics by running harder or softer pressures, so long as those differences are equal from side-to-side (and within reason from front-to-rear), your alignment should be fine. Just make sure your alignment guy doesn't set the tires back to spec. Tire pressures are the first thing an alignment guy should check prior to starting.

Scott

 

[PontiacHO]

We used to align patrol cars fully equipped with the officers’ gear to ensure optimal alignment. Yes caster can be off due to under inflated rear tires and/or weight in the trunk. We had several massive patrol officers (400 lbs) and we asked them to sit in the driver seat to set their front ends…..

 

[JHZR2]

We used to align patrol cars fully equipped with the officers’ gear to ensure optimal alignment. Yes caster can be off due to under inflated rear tires and/or weight in the trunk. We had several massive patrol officers (400 lbs) and we asked them to sit in the driver seat to set their front ends…..

That’s what I understood to be the gold standard. For Mercedes, the right way to do at least the older ones is to apply a spreader bar between the wheels to exert some spreading force on the wheels.

Soft, sloppy, under inflated tires I would think might shift a bit. But how much of a difference I would suspect is tire and suspension-dependent.

 

[Jetronic]

The first step in an alignment is to set the correct tire pressure.

If the pressure was set a few psi above or below the pressure the owner runs the tires at, would that affect the alignment in any way and if so, how and how much?

Uneven pressures can deflect the suspension (esp side to side but also diagonally), as long as it's even the higher pressures don't matter.

 

[willbur]

We used to align patrol cars fully equipped with the officers’ gear to ensure optimal alignment. Yes caster can be off due to under inflated rear tires and/or weight in the trunk. We had several massive patrol officers (400 lbs) and we asked them to sit in the driver seat to set their front ends…..

I seem to recall BMW used to recommend engine running so ps pump would load the steering components