Alignment Recommendation of Ohlins FP Specs
 

I need an alignment recommendation for my 2-year project just rebuilt 94' Touring. This is a primarily an often aggressively driven street car with occasional track days.

Rebuilt specs:
New FP Spec with spherical upper mount Ohlins from SBG with Touring setup (10kgfront/8kg rear)
New stock-like aftermarket pillow joints, standard SuperPro poly bushings in non-360 degree positions, and Mazdaspeed bushings in 360 degree positions
New heim-joint trailing and toe arms rear
Front ride height 25 3/8", rear 25 7/8"
New BBS RGR 17"x9" front with 245/40/17 or 255/40/17's tires (haven't decided yet)
New BBS RGR 17"x9.5" rear with either 255/40/17 or 265/40/17's tires (haven't decided yet)
Racing Beat front sway with front brace
Currently no rear sway but I have Racing Beat rear sway if necessary
Banzai differential and transmission cross member braces

My thoughts:
Front tires 30psi, rear tires 27 psi?
1/16" to 1/8" front toe-in, no rear toe
-1.2 to -1.5 front and rear camber?
minimum caster?

Does the spherical upper in the Ohlins coilover change the amount of camber or caster needed?

Thanks for any help
Mike

couple thoughts, on a 9" wheel i'd run the 245, and the 9.5 the 255. we did some tire to wheel size testing, and a little stretch is good.

for a street car you want to start with the cold tire pressure on the door sticker (should be 32?). for a track car, hoosier has a tire pressure to weight to section width chart, and i'd start there.

you want zero toe in the front and a little toe in in the rear.
for a street car you're about right for camber, i'd do -1.5 in the front and -1.2 in the rear
Castor is up to you, if you can do around 5 that is probably good, its pretty subtle.

for the shocks, either set them where ohlins says to and call it good, or try full stiff, and then full soft, and then about half way, and see what works. full stiff and then full soft calibrates the butt dyno.

further reading: http://farnorthracing.com/autocross_secrets.html

My car is basically a street car with occasional track days (i.e. 1-2 days a year). Toe in front vs. rear vs. neutral both? One other question I still have is the spherical upper on the Ohlins FPSpecs. Does this change the thinking concerning camber and/or caster?? Since a "normal" coilover has no movement at the upper portion of the strut mount, camber and caster are fixed and can only change during tire loading and cornering. With this spherical upper, does this change the dynamics in a way than the amount of camber and/or caster, particularly camber of course, is affected by tire loading and cornering so that amount of camber should be increased front and rear given the upper "give" so to speak due to the spherical?
Mike

small amount of toe in on the front and zero toe rear is my recommendation for a FD that's driven in a sporty fashion. The more toe-in you have up front will make it more stable in a straight line but also slow response a bit (which is already slow on the FD in my opinion). So more toe in up front for street, less toe in up front for track. I've run zero toe in the rear for 8+ years and never found it to be an issue, but mine is mostly track time so maybe it's a little less stable on the street.

I don't think the new upper mount will have a material affect on the amount of camber gain through the suspension travel. It will help not have "stiction" in the suspension, but I wouldn't adjust camber values for it. Your choice on camber is going to be affected by how much tire you're trying to fit and how sticky they are. Since it'll be mostly street you'll want to run as little as possible that you can to still clear the fenders to slow inner tire wear. More track oriented setups with stickier rubber would need more camber. I've found that having the rear about 0.2-0.3 degrees less than the front gives pretty similar tire wear front/rear and balances the car well (so if you're -1.8 in the front go -1.5 or -1.6 in the rear). Hope that helps.

I wouldn't think it would cause camber gain but camber loss. A stiff strut would keep the camber set but the spherical would allow the otherwise stiff straight upper portion to give some even with the car at rest. What happens then with load is the question?? Does the camber even decrease some more(more give at the spherical), does it stay the same or does it even increase some, which I would doubt?
Mike

The FD has a double a-arm suspension not a strut suspension, so it functions differently. The FD suspension does experience camber gain and not loss as it goes through its travel and the shock does not have any direct effect on the angles of the suspension as it moves through its travel other than limiting how much travel there can be. Therefore the only way that the spherical mount could have any effect on camber would be if it allowed the suspension to move further in its range than the non-spherical by being less "sticky" or resistant for a given load. This amount of movement change would be SMALL at best and would not have any material camber change in my mind.

I understand. I didn't mean to say a true strut suspension, my meaning was more to the fact the upper part of the strut or shock or coilover or whatever is fixed or rigid. I also understand the camber gain as compressed. Thinking about it, I agree that the potential change in the camber would be small with the spherical upper. Just not enough potential lateral movement toward the wheels of the upper portion of the spherical coilover to make any significant difference.
Mike

the shock/strut has nothing to do with camber on an FD, you could remove it, and camber would not change. camber is defined by the upper and lower control arms.

That makes sense if the upper and lower control arms are equidistance from wheel center and are the same overall length to the knuckle joints, which I assume it is. A fixed camber throughout entire compression range. Got it. Thanks.
Mike

Mike can you elaborate on this a bit? Are you saying you have the MS bushings in the multi-axial joints such as the rear trailing and rear control arms? And the rest are poly bushed?

The rear lower control arm inners are 360 degree bushings, those are the ones that need to stay non-poly. The 360 degree shock bushing can be poly or OEM, not as important so I stayed poly. I bought the Mazdacomp 40% stiffer ones through Mazdatrix for the rear lower control arm inners. You can stay standard stiffness OEM too, Mazdatrtix sells those too. You need two, one for each side. Mazdatrix item 28-4600-F128 for the Mazdacomp. The pillows are the aftermarket J-Auto ones.
Mike

One more thing, my rear trailing arms are aftermarket with Heim joint ends, also 360 degree-type bushings. Could stay OEM also if you wish.
Mike

ok great, that's what I thought. Thanks!