My current geometry

[CarJunkie]

I get a lot of questions about my chassis setup, and my progressive changes have been discussed in various threads over the years, but I thought I would update where I have ended up, with a setup that I am VERY happy with!

Hardware:
I run Ohlin's R+T coilovers with their springs, lowered about 15mm front and 5mm rear, Vorschlag camber plates set to the lowest caster setting (stock caster, with change resulting only from ride height adjustment), and the M3 convertible front sway bar properly balanced with Turner adjustable links.


Evolution of alignment settings:
On stock staggered setup, I found that a 1 degree difference in camber front to rear produced very neutral cornering balance, with the hardware above and RE71r tires (255/35/19 front, 275/35/19 rear) at autocross and track.

I used a set of RE71r's at -2.7f/-1.7 rear and performance was good, but there was excessive inner tread wear in mixed street and track use. To reduce negative camber wear, I did one season on RE71r's with -2.5f and -1.6r and overall grip suffered. They still wore excessively at the inner edge, so damned if you do, and damned (plus slow) if you don't. I then gave up on trying to find a solution that would compromise tread wear and performance.

In 2018, I mounted PS4S (again 255f/275r) on my stock wheels for the street and to be a backup for rain the track. I accept that they will die early from inner tread wear, but not before I have a chance to heat cycle them a few times on rainy track days. I got a square set of wheels (Apex Arc8 18x9.5et22) for the track.

I settled on -2.8f/-2.2r for overall grip balance. This will presumably understeer at the limit on stock tires (haven't really explored that yet), since with square setup it is perfectly balanced. At the track, the car has sharp immediate turn-in without trail braking, is easily controlled mid corner with a 4 wheel drift at the limit, and no hint of understeer when feeding on throttle at corner exit. I haven't had a chance to run the staggered setup on this alignment at the limit yet.

I believe this alignment is perfect for my driving style. This year I used Toyo T1R's. Once I got hot pressures dialed in, tire temps were perfect across the tread. My tires corded at the inner edge, but the wear was even enough that no change in alignment would have gotten more than another session or two out of them.

My car was driven by an former Porsche professional driver development coach who has literally driven everything, and he said "I don't know what you have done to this car, but it's brilliant. I am in love."


Rubbing:
I have the revised fender liners. I use a 10mm spacer on the front only with my stock wheels, which undoes the excessive top tuck resulting from the aggressive negative camber. With spacer, my stock fronts with RE71r 255/35/19 tires rub at the top under cornering and compression, not enough to worry about. My right front also rubbed on the right only when turning right where there is a bulge behind the wheel on the right wheel well. This bulge is not present on the left where the tolerance is tight, but no rub. The RE71r's are wide and wore down the plastic there on the right side bulge, but not enough to create a hole. The PS4S in same size does not rub there, and probably doesn't rub at all. Who knows if it would rub if the two sets of bridgies hadn't done some clearancing work.

With the track wheels, no spacer on front, big compressions cause a rub on both sides. They don't rub at the rear side fender bulge.

Note that increasing caster even 1 step up on the camber/caster plates would worsen the rubbing on the right side behind the wheel, and probably also produce rubbing in the left. Increasing caster from the top only moves the wheel rearward in the wheel well. There are caster control arms that work from the bottom and you would really need to do both to maximize caster while maintaining clearance for the widest tire possible.

I'm just happy I can fit a 275 all around. The lower diameter helps.

My rears don't rub at all, 275/35/19 on stock wheels with no spacer, or 275/35/18 on track wheels with or without 10mm spacer.


Pictures:
Current alignment (did I mention I love it?)
Side view with OEM wheels (10mm spacer on front only)
Side view with track wheels (10mm spacer on rear only)

[PRTSB1M]

Can you post pics of tire to suspension clearance on both street and track setups?

[CarJunkie]

Originally Posted by UN1CORM

Can you post pics of tire to suspension clearance on both street and track setups?

Just snapped these, stock wheels. I would estimate at least 4cm clearance to the rear shock, probably 2cm clearance to the front spring, although much harder than rear to get a good view with car on the ground. That's with 10mm spacer on front.

I won't have the track wheels on the car until April. At 9.5" wide, the front is wider than stock by 1/2", and sits slightly more outboard than stock wheel + spacer. My guess is it's also a little closer to the spring, but can't confirm. The rear tucks inward compared to stock, but with 10mm spacer is returned to the same outer position, so probably similar clearance to shock without spacer, further away with spacer.

[PRTSB1M]

Originally Posted by CarJunkie

I got a square set of wheels (Apex Arc8 18x9.5et22)...

What was your reasoning for choosing these over the 18x10 et25s?

[CarJunkie]

Originally Posted by UN1CORM

What was your reasoning for choosing these over the 18x10 et25s?

They were a 1off color, and were discounted, and I snatched a great deal. They were offered for $250 each, bought 4, then APEX only had 2 left and offered them to me for $125 each. 6 wheels for $1250. Can't complain!

[PRTSB1M]

I'm definitely following most of your recipe, but decided to go with the safety car spec of 255/35 front and 285/30 rear (PS4S new size, backordered) for street setup. Using the default height settings in Ohlins instructions this should net a 12mm drop front and rear (compared to stock) and a little gearing advantage. I don't plan on running spacers or changing out the front sway bar, and will likely start with stock alignment to see how the car feels before mas camber. Not that it affects geometry, but I also picked up BW monoballs for the front tension arms.

[CarJunkie]

Originally Posted by UN1CORM

I'm definitely following most of your recipe, but decided to go with the safety car spec of 255/35 front and 285/30 rear (PS4S new size, backordered) for street setup. Using the default height settings in Ohlins instructions this should net a 12mm drop front and rear (compared to stock) and a little gearing advantage. I don't plan on running spacers or changing out the front sway bar, and will likely start with stock alignment to see how the car feels before mas camber. Not that it affects geometry, but I also picked up BW monoballs for the front tension arms.

Please post a pic after getting the 285/30 mounted on the wheels (stock359's I assume?). I am curious to see if they will look noticeably more square than the fronts. 255/275 still look slightly stretched on the rim mainly due to the beefy wheel protection strip. I may also go with 285/30 next time.

[PRTSB1M]

Originally Posted by CarJunkie

Please post a pic after getting the 285/30 mounted on the wheels (stock359's I assume?). I am curious to see if they will look noticeably more square than the fronts. 255/275 still look slightly stretched on the rim mainly due to the beefy wheel protection strip. I may also go with 285/30 next time.

Will do, and yes they're going on the stock 359s.

[PRTSB1M]

Originally Posted by CarJunkie

Please post a pic after getting the 285/30 mounted on the wheels (stock359's I assume?). I am curious to see if they will look noticeably more square than the fronts. 255/275 still look slightly stretched on the rim mainly due to the beefy wheel protection strip. I may also go with 285/30 next time.

This isn't a PS4S, but looks pretty square to me.

[PRTSB1M]

Just found out this is also the same spec as M3 GTS. Great tire shots of one here:

[PRTSB1M]

There is still the tiniest bit of stretch…

[PRTSB1M]

Originally Posted by Tiana

Can you say your wheels name? looks great!

They are the original wheels from BMW, style 359M.

Here is a comparison of 275/35 vs 285/30

[PRTSB1M]

I don't know if it is the better compound of the PS4S or tire geometry, but having driven on the 285/30s for a few weeks it is definitely harder to break traction than with the 265/35 PS2s that came on it or the 275/35 DWS06s that were on it before.

There is a nice sweeping curve near me that I always used to kick the back end out on in MDM (mini-drift) and the car simply will not come loose there at safe speeds like it did before, just slams out of the corner with a tiny flicker of DSC.

[PRTSB1M]

Originally Posted by CarJunkie

Just snapped these, stock wheels. I would estimate at least 4cm clearance to the rear shock, probably 2cm clearance to the front spring, although much harder than rear to get a good view with car on the ground. That's with 10mm spacer on front.

Are you able to run the stock 359M wheels with 255/35 PS4S without the 10mm spacer up front or does the tire rub on the ohlins somewhere?

[CarJunkie]

Originally Posted by PRTSB1M

Are you able to run the stock 359M wheels with 255/35 PS4S without the 10mm spacer up front or does the tire rub on the ohlins somewhere?

Yes, and I ran that tire size with Bridgestone RE 11's (much more chunky and wider) without a spacer and had plenty of clearance to the stock springs and to my coilover springs. I mainly run the spacer for aesthetic's because I have so much negative camber.