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Front: 2.8 degrees negative camber, .12 degrees toe-in
Rear: 1.9 degrees negative camber, .30 degrees of toe-in(factory is .37)
Michelin PS4S 265/35/18 tire on 18x9.5" wheels
Car weight is 3070lbs with 5/8ths tank.
Weight balance is 52.09% front, 47.91% rear, cross weight is perfect
Tires are kept at 38psi hot. I start at 35psi cold and deflate when necessary.
All suspension components are in perfect condition, most are monoballs. AST coilovers with 350lbs spring front and 550lbs spring rear, car has a small reverse rack(rear end is lower by .3 inch). (343lbs/429lbs after motion ration calculation. The bounce frequency will be 1.93f/1.96r.) I also have a 30mm hollow front sway bar set to middle stiffness.
M3 sees some track time but most of the driving is done on back road twisties like Tail of the Dragon. This set of tires were only driven on the street. This is not a daily driver and only leaves the garage to be driven around twisty roads.
The problem as seen in the attached photos is the front tires. Outside edge is bilstering, inside is in on cords, middle has 4/32nds of tread. Both front tires look like this.
Yay someone else with sane ride frequencies!
So based on only mentioning the front tires, I'm just going to assume the rears are fine (Or atleast tolerable in terms of wear). Tires wear, generally speaking, based on heat. The heat in turn simply comes from how much load each section of the tire is carrying. If you grab a IR thermometer, or pyrometer and take some temperatures driving in a straight line I would imagine its a fairly safe bet that the inside of your tires will be hotter than the middle or outside due to -2.8 degrees of camber. This would account for the inside tire wear.
If you preform the same test and record temperatures around a skidpad of averageish radius, it seems likely that your outside will be hotter. However, dynamic conditions vary significantly more in cornering than straight line, so there's a few possibilities. For starters, You see camber change resulting from steering angle: KPI*1-cos(steer angle) - caster*sin(steer angle). For a tighter turn, or a larger steering angle, you'll see different(more) -camber gain than a larger radius turn. If we assume -2.8 camber is correct at some point, you may simply not be driving through turns you were setup for. Re-evaluating your camber is generally a beneficial test to do, even if it's not the cause of your issues.
For the center of your tire pressures is the likely culprit, however you may be forced to simply choose what wears faster, inside or outside. If you cant get even temps across the tire, simply do the best you can and accept that one part will wear faster than the others depending how much of your time is spent cornering.
I'm less inclined to blame toe given how close to factory you are, but it's still worth mentioning. I may be over estimating oem engineers, however for a performance oriented car, I would expect bushing compliance and the toe curve to be opposite eachother, and cancel themselves out(or atleast attempt to). When the outside tire is heavily loaded, the bushing compresses altering your toe. If the toe curve changing due to body roll then goes the opposite direction, it keeps your toe close to where it was set. If you remove the bushing compliance from this with a monoball, you now simply have toe change with nothing counteracting it. This would likely just cause wear on the tires.
Basically, it's all a huge balancing act between alignment settings. Depending on what adjustment you have available, you could reduce your -camber, and increase caster to aid the inner tire wear while maintaining the same -camber while cornering, or reduce -camber and kingpin. With a macpherson front there's no shortening your upper control arm to make your camber curve more aggressive to directly target it, you're stuck with your camber curve being directly tied to kingpin inclination.
As a general rule, that wear pattern is characteristic of too much caster and excess negative camber.
As Robbie said, as caster is increased so does the effective negative camber, the tyre will ride up on the shoulders more as the steering it turned from straight ahead and more load will be applied to them, you can observe this as the actual camber of the wheel changes with applied lock.
The camber will be a problem as there is much more wear of the lightly loaded inner edge, so normally that would be reduced to even out the tread wear - however, there are the two complications of the caster induced camber change AND the possible camber of the roads the vehicle is driven on. The latter is because most camber settings are for track and/or wide, flat roads but may twisting country roads have quite a lot of road camber - the middle is higer and carves off to the road edge - and this changes the way the tyre interacts with the road surface, effectively adding negative camber.
There may also be a problem with the ackerman angles.
You don't mention wheel and tyre widths, if you are using the idiotic 'stretch, rather than correctly sized tyre for the rim - or vice versa - you will also be introducing a complication of the inverted trapezoid shape of the wheel/tread and sidewalls stiffening the tyre sidewalls and reducing compliance.
Thre are going to be a bunch of things you can do, if not already, such as trying a little toe-out on the rear, stiffening up the rear rebound, a stiffer rear ARB, etc, to improve turn in as I suspect that is part of the problem with initial understeer.
Thank you guys, I will reply later but the wheels and tires I use are below.
Michelin PS4S 265/35/18 tire on 18x9.5" wheels, et35 front and et22 rear. Not stretched nor over-wide.
Yup, spec' width 9.5", so you're right on the sweet spot!