rotating top hats for caster adjustment...

[n2o_matt]

I've seen a lot of people running lots of angle adjusting caster at the top hat, guessing this is so you can still have the wheel centered in the well and not have to worry about the LCA bushing binding.

My question is, how much caster do you run? I see every one recommending 7-7.2, but that is about stock, so why rotate the top hat? Can this still be accurately measured on a laser rack that uses a steering sweep to measure caster?

Also, has anyone had issues with very tough steering (only) at high angles while sitting still? Seems like this would be caused from jacking, which is increased with caster iirc. However, my steering is also very slow to return from high angles (especially at low speed).

I'm running keisler knuckles (zero ackerman knuckle) and I still have my PBM rack spacers from my old setup - could this be part of my problem? Maybe I'm going into reverse ackerman?

Thanks guys

[BenRice]

The idea with rotating the strut top to pull the top of the strut towards the front of the car is to "stand up" the wheel when on lock. You can achieve some of this with a lot of negative camber at the lower mount (some coilovers run offset bottom mount holes, or oval top holes to achieve this) but you then run into the issue of big static camber and bad tyre wear when driven straight, especially if daily driven.

Best way to describe the "standing up" of the front wheels is winding the steering wheel all the way to the right. The RHS wheel will point out, but when looking directly at the tread of that wheel, you will see the wheel is now rocking positive camber (the LHS will have a lot of negative camber). I measured the camber on my RHS on full lock and had +8.8.

If you wanted a better contact patch you can either increase the length of the castor arm (and lose the self centering effect and reduce the tyre-guard clearance on the rear part of the arch) or you can pull the strut top forward by rotating the camber plate.

I did this with my BC Gold's and without changing anything else, reduced my positive camber to form +8.8 to +7.8 at full lock and reduced my static camber from -4.8 to -4.3.

It now feels a little better and i know i'm getting slightly better tyre wear. I obviously don't drive on full lock all the time when drifting, more like half to 3/4 lock, but I know the contact patch has improved and the camber change from static to full lock has less of a range to go through. The self-centering is still there so I'll reduce my castor from 7.8 to closer to 7.5 at my next alignment and see how that feels.

The stiff feeling could be due to leverage and resistance: what size tyres are you running up front? And have you moved the rack forward on the cross member?

Hope that helps.

[n2o_matt]

Thanks! That's what I figured, but isn't moving the top hat like that actually changing the castor, just not with the lower castor arm?

I think that alignment machines basically measure the amount of camber change they see as the wheel is turned x number of degrees, so I'd be surprised if when you go back to get an alignment you didn't already have less castor than the last time you went. But that sounds like a lot of caster either way.

Yes, the rack is moved forward using the PBM steering rack spacer/relocators. Tires are 235 40 r17 on a 99' mustang wheel with no spacers (need some actually to get some clearance...)