Tire wear opinion
 

Hey guys, I took my BRZ to a local track this Sat and within about 1 hour of track time, I pretty much killed off my front left tire. The track had more right handers hence it's natural the front left would take the most abuse. The tires are Nexen SUR4G that has had a couple hours on them but the tire started the night off pretty worn pretty evenly. The wear in question is on the OUTSIDE, not inside. I have attached a couple images and wanted to know if the problem is my alignment (not enough negative camber @ -2.5), tire pressure (I was @ 38 hot) or user error (overdriving the tires). Any opinions?

Need more camber

Since Mac struts don't have a dynamic camber curve, any amount of body roll works to subtract from your negative camber. If you have -2.5* of camber but get 2* of body roll across the front axle it in effect is like having only -0.5* of camber.

You can A) Add lots more camber like >4 or B) stiffen the front to reduce roll or (A)+(B).

Alternately, you can also consider rotating your tires after every session.

Thanks guys. I didn't think of body roll as I am only on SACH + JDM pinks. Figured I wanted to be comfier this time around as I am getting older. I wouldn't want to add much more camber since this is a street car so maybe I will need to up spring rate and add just a hair more camber.

Stiffer front swaybar is a pretty streetable compromise, doesn't promote much understeer for whatever noodly suspension dynamics reason, just sharpens up the responsiveness and adds grip.

My aggressive street camber would be -3 up front.
Currently -4

I already find the car understeering at the limit. It will rotate with enough steering angle and lifting the gas but in large, it tends to push. I am scared the a bigger front sway will make this problem worse. But it's gonna get expensive though if my tires is going to look like that after every outing. hummmm......

The bigger bar keeps more of your tire on the ground. It may even make the car rotate more.

Yea a bigger front bar sounds reasonable seeing how much grip you added over stock. I noticed no understeer from going to Perrin adjustable bars front/back. If you do you can always play with the adjustment on the bars.

My previous race car had double A-arm front suspension so having roll across the front axle improved front grip because it didn't lose negative camber with roll and the roll put weight on the tire while properly working the contact patch.

So with this car, for the sake of getting the front to work (better) I started with the sway bar on the softer setting and experienced quite the understeer. So instead of going stiffer, which felt to me would make it worse, I added stiffness to the rear - now the car would understeer on entry and be even worse on exist with oversteer. Not an improvement. So I finally ended up going back to softer rear bar setting and the stiffer front bar setting and BOOM! The front end worked MUCH better on entry and rear was better on exit. Then it was a matter of fine tuning rotation with toe and tire pressure.

Keep in mind that I have to run specific bars due to the rules but they had soft/stiff adjustment points and I ended up soft rear, stiff front.

Good luck.

More front camber will reduce understeer as well. You are clearly not using the whole tire, pretty simple solution imho.

Even with a 6k spring and swaybar approx ~20mm solid full stiff I need -4 degrees to use most of the tire. I found the car decently balanced at -3 up front and -1.5 rear camber but everything else stock, that might work out based on just having the sti springs and alignment, you'll still get outer edge wear though, idk, you either add the grip and stiffness to the front or reduce grip from the rear to balance the car, I know which one felt faster to me.


You're not the first to avoid a stiffer front bar because 'that makes understeer' but it just plain works on this chassis, and you won't be the last to see that if you decide to do it.
Eibach 25.4mm or Whiteline 22mm might be a bit much unless you're playing with aero and slicks but on full soft they'll probably be good with the sti springs, perrin/whiteline 20mm bar would be my suggestion, maybe the perrin 22mm or Megan 25.4 if you plan on stiffening the springs and really going after the 200TW one lap hero TT class.

Total bullshitting out my ass but I think the stiffer front swaybar works because there's so much mass rolling around between the front wheels from the engine, the car is 54/46 static weight distribution, c.g. like a few inches in front of the shifter, car just wants a lot of roll stiffness up front to compensate for it and the OE spec is to make it a somewhat passable DD, not necessarily to make it 'balanced'.

I'm convinced all the car magazines call the 86 'balanced' because 99% of what hits the roads these days is an understeering pig and the bar is so low Subaru tripped on it and still got applause.

Yup. Just want to add some support to this logic. It's counter-intuitive, but it works. It's not just this chassis, but it's most every other platform that have a "suboptimal" relationship between dynamic camber and roll (among other factors). You've probably also heard of the logic that when you add stickier tires, you need stiffer suspension - this is part of that. With stickier tires, you now need to account for the increased load and resulting roll. It's just that this chassis is particularly bad when it comes to how much it rolls vs how much static camber it has (none) and camber it gains (loses) at that amount of roll (and steering). Reduce understeer by reducing roll to prevent/reduce the suspension going into the part of the camber curve where the tire contact patch becomes less optimal. It works until you start to exceed how much load the tire can handle, then you're getting into the conventional understanding of ARBs.

As a side note, perfectly even tire wear (including temperatures), isn't always a reliable indication of optimal tire performance, tire pressure, etc. There's a range of camber that every tire still generates peak/near-peak grip. Sometimes what's fast results in less than ideal or even wear and temps, so you're not always aiming for net zero camber when the car is loaded up in a corner.

If you're interested in comfy ride, don't bother with adding sway bar stiffness. I just went with Eibachs front/rear (a *lot* stiffer) and while it is a big improvement at the track, the ride is more busy on the street for sure!

You might consider getting Bilstien B6s, they are way smooover than the SAchs, and also have more bump travel which should give more front grip as I bet you're on the outside front bumpstop under hard cornring now.

Moar front cambers is a good idea. I run -3.5 to -4 front and -2.8 rear for street and track. It's WAY better than what you have now for track, and not as bad as you might think on the street. My street tires have seen some track time plus 8-10k street miles and have worn evenly overall. Now at ~3-4/32 remaining.

Thanks for all the suggestions. I feel like adding a bigger front sway bar and adding camber is the simpler/cheaper route to take, even if it means for a busier ride. However, it won't be easy adding front camber as i am only on bolts and i have maxed out the setting. Maybe it's time to get coilovers with camber top plates, like Fortune 500 or RaceComp T2 so you can dial in spring rates, get some adjustability and get camber plates. So much to do with so little money.... :)