A question about caster…
 

A couple weeks ago, I hit a curb in the BMW 330, enough to just barely bend the wheel. I have low profile tires, so I’m not surprised about that. That said, I took it in yesterday to check the alignment, and the caster on the left side is less than the right side.

The left is +6.1 and the right is +7.0*. I have adjustable camber plates, but that’s all we could get. The car pulls to the left just a little bit. So this tells me something’s up.

After I pull the wheel, I’ll check everything and see if anything is obviously bent, etc.

If I can’t find anything, what do you think about making the right side match the left, at +6.1? Is there any downside to that?

* This is the way the race shop set it up in addition to camber and toe for the track.

Thinking you might find that you tweaked a tie rod just a bit...I'd talk to a good alignment guy about doing the matching thing.

probably bent something other than the wheel. a 1 degree difference in caster isnt that much actually, and pretty common, at least in old busted up race cars that i do alignments on.

caster is a second order effect (ie it only effects changes when something else changes), unlike toe and camber. so i wouldnt expect a pull to come from caster. maybe if its real gittery over bumps, but again, thats usually a bad toe.

it shouldnt pull if the camber and toe are setup properly.

Swap tires and see if it still pulls.

I would replace the lower control arm while you are in there.

+1 on the lower control armS. They're a wear item on a 330 anyway.

I'd match caster left to right either way (or at least not more difference than the spec).

Assuming a car that tracks/drives straight and then adding additional caster to one side only would have the effect of making the car want to pull towards the opposite side that has less caster. (or removing caster from opposite side.... same result)
The more the caster angle, the more leverage the weighted wheel has trying to rotate up about the slanted pivot axis.

I used to have a bunch of caster dialed into my oval track dirt car for weight jacking/traction in a turn and that thing would pull like crazy when taking a test drive down a paved straight road. If you let go of the wheel it would drag you off the road instantly.

BMW's have front strut assemblies which form the pivot axis for caster and I think the only way for caster to change would be for a lower arm to have bent back a bit thus lowering the caster (because the lower portion of the strut is now located back a bit). Slight caster adjustment could possibly get done at the top with some aftermarket adjustable strut tower mounting plates but probably not much.

Listen to Tim.

Thanks guys. I’ve replaced all the suspension pieces, so the control arms only have a couple thousand miles on them. For grins, I’ll probably go ahead and replace the control arm, and I need to look at the control arm bushing. It’s possible, the curb pushed the control arm back and into the bushing…

Random side note. I picked up an absolutely INSANE hitchhiker in a blizzard one Christmas Eve. He talked about lots of odd / weird / insane crap. But, he was fixated with Caster and Camber...