Endurance track tires + less SAI = less sidewall rollover at the track?

Track noob here (5 real DEs under my belt), planning for this season.  E90 M3 6MT, mainly a street car, close to stock.

Been running PS4S in the stock 245f/265r sizes.  I've been more than happy with them, except that they're rolling onto their outer sidewalls too much.  I'm sure I could fix that by dumping a bunch more camber and air into them, but that doesn't seem ideal.  I'd like to keep a streetable alignment setting (no more than -2º) and not have to mess with it before and after each DE.

My current plan is a combination of two things:

1.  Tires.  I get the impression that endurance-focused track tires have much stiffer carcasses than the PS4S without adding a ton more grip.  I'm imagining this would mean less deformation on average at a given camber setting.  Looking at AD09, R-S4, and NT01, in that order (ECF doesn't come in my rear size).

2.  Reduced SAI.  I'm planning to swap in in camber correction spindles from an F8x M3/M4.  These add a bit of negative camber (around 0.5º), allowing me to dial some out of my camber plates (more upright struts = less SAI = better camber retention on the outside wheel).

Does this make sense?

I'm sure there's no way to know if it'll will work without trying it; I just need to know if it seems worth trying.  If not, I guess I'll have to stick with PS4S (the spindles are going in regardless) and just deal with alignment changes before and after each DE.

Thanks (for reading, if nothing else)!

Excessive sidewall roll is unique to PS4S.  Lotsa air can help, plus correct camber.  And plenty of wheel width.

But the better answer is different tires. 
 

I will never be convinced that changing SAI or caster have any meaningful effect on camber at the steering angles typically used on track, unless you are drifting.

Changing SAI will definitely affect the camber curve and roll center, which may or may not be beneficial, and changing caster will affect the tie rod height so it will affect bump steer.  But the effect on camber at the steering angles we are talking about is small compared to control arm deflection, upright deflection, etc.

Andy Hollis said:

Excessive sidewall roll is unique to PS4S.  Lotsa air can help, plus correct camber.  And plenty of wheel width.

But the better answer is different tires.

Thanks.  That's what I figured.

Think I'm on the right track with the ones I listed (AD09, R-S4, NT01)?

First off, 2.5-3* of camber is plenty streetable. For a front heavy, fairly heavy overall car, you really just want more camber. Beyond that like Pete said I don't think the steering axis effect on camber gain *from steering* is very substantial. But if you look at the front view of the suspension, it also has an impact on camber gain from suspension compression, in the other direction (ie more sai = more camber gain). The only slight downside is that leaning the strut in more reduces the motion ratio a bit which reduces the effective spring rate.

If it was me I'd do the knuckle swap and keep the camber plates maxed out, and maybe play with the toe a little bit to find a setting that drives well. Different cars react differently but I've owned/driven a few different cars with 2.5-3.5* camber and they all drove fine on the street.

IamFODI said:

 

Thanks.  That's what I figured.

Think I'm on the right track with the ones I listed (AD09, R-S4, NT01)?

Given the usage you mention, what you are looking for is a trackable street tire, as opposed to a streetable track day tire. 

PS4S is one option, but with the setup/wear downsides you have experienced.  Conti ECS02 is a better version of that style tire, with a bonus of being inexpensive.  Both of those are also amazing in the wet.

If wet is less of a concern for street use, AD09 is a fantastic tire. Read the two tests which include it.  Grade A driving dynamics.  A bit pricey though, but right there with Michelin.

Moving down your list -- RS4.  Cheap, super long lasting, not great in the wet. A bith rough on the street.

NT01 = meh -- super old tech.  More modern stuff is a better option, IMO.

Conti ECF is a pretty decent tire on the street in my experience...not sure if offered sizing fits your application.

My ATS-V has -3.0 front camber via Vorshlag plates, and works just fine on the street.

Andy Hollis said:

Given the usage you mention, what you are looking for is a trackable street tire, as opposed to a streetable track day tire. 

PS4S is one option, but with the setup/wear downsides you have experienced.  Conti ECS02 is a better version of that style tire, with a bonus of being inexpensive.  Both of those are also amazing in the wet.

If wet is less of a concern for street use, AD09 is a fantastic tire. Read the two tests which include it.  Grade A driving dynamics.  A bit pricey though, but right there with Michelin.

Moving down your list -- RS4.  Cheap, super long lasting, not great in the wet. A bith rough on the street.

NT01 = meh -- super old tech.  More modern stuff is a better option, IMO.

Awesome.

Not worried about street use, livability, or wet performance; these will be on a separate set of wheels for track use, and I'll keep my current wheels with PS4S for street use and/or a literal rainy day.

I read and loved GRM's tire tests.  Super helpful.  They're actually why I ranked AD09, R-S4, and NT01 in that order. 

Looks like AD09 is the move.  Driving dynamics, particularly communication, are super important to me – not just to learn with, but for fun.  So, if you think that tire will also offer the consistency I need with grip levels not too much higher than PS4S, I'll try it first.

Thanks again, Andy!

flyin_viata said:

Conti ECF is a pretty decent tire on the street in my experience...not sure if offered sizing fits your application.

My ATS-V has -3.0 front camber via Vorshlag plates, and works just fine on the street.

I can do ECF if I run 18" front and 19" rear, but

1.  I don't feel like hunting for another pair of rear tires, and
2.  I get the impression that ECF's main advantage over the AD09 is grip, and I don't want the car to be even better at hiding my mistakes than it already is.

Happy to hear if you disagree!

I don't think the ECF is *that* much stickier than the AD09, and tends to be less expensive (at least in the sizing that works for me).  They're unbelievably consistent for HPDE, my current set has I think 37 DE sessions on them and I could easily get north of 50.