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.... :)

Look into pedders top mounts. They can get you over -3° with your current setup.
They're hard to get a hold of lately due to backorder but will add roughly .75° additional over just running bolts.

If you're worried about understeer, get front *and rear* sways. In addition to taking load off the outside front, a stiffer rear sway will further limit roll, reducing camber loss

Since we got that out of the way, driver inputs are probably a huge factor. I know the OP mentioned adding steering angle and snapping off throttle to rotate the car. You are probably going to burn down your tires regardless of camber if you do that much at all.

I certainly wouldn't ruling out that I over drove the car but I should clarify the comment above. I am not turning the wheel more while the car is pushing and lifting to cause rotation. What I meant was that when the car is turning with grip with a certain steering angle and if I lift off, the car will rotate. I have also noticed that power oversteer is easier to achieve with more steering angle.

Interesting data about adding front ARB adding front grip by optimizing dynamic camber.

To folks who experienced that first hand, what camber did you have where this helped?
Does it help primarily if you have insufficient camber to begin with (e.g. -1.7º),
or does it help even if you have 3–4º of camber in the front?

What is the typical º of roll a car with say 6 kg/mm springs has with stock ARBs and 200–260 TW tires?

It would depend on tire grip level as well I think.

There is some really good information on swaybars in this thread. https://forums.nasioc.com/forums/sho...d.php?t=879235


Attached is a suspension calculation spreadsheet that was posted on NASIOC back in the day. I don't see why it can't be adapted to the BRZ/FRS by changing some of the parameters.

This is awesome, thank you!

It is probably more important with less camber, but if you look at the STX setup thread, you'll see that most people there are running -4 to -4.5 degrees camber and a bigger front bar.

I use Pedders top mounts along with double camber bolts on Koni Yellows and TRD springs.
My alignment guru found he could get maximum -3.5 front camber although we settled at -2.75 for my combination of 99% DD (commuting) and 1% lapping.
I’ve yet to track this set-up due to COVID closures and moving across the province recently but hope to bolt on the new A052’s and get at it soon. Perhaps Friday.

Yup, at -4 with a 6k front spring super 200tw tires and I wouldn't go back to a stock front bar, just keeps the front end planted through sweepers and makes the car mega responsive through slaloms.

Again I think they under spec the front bar because 95% of these will never ever be driven at the limit. Just because the factory sticks it on doesn't mean it's good for track/autox, car probably would've been a little better with a 21-22mm tubular or 19-20mm solid

Well, I guess past a certain amount of total roll stiffness the benefits for AutoX are not in dynamic camber but rather quicker transitions; meaning that steady state cornering / grip in "longer" corners start to suffer.

Eyeballing at photos of my car at the track, the dynamic camber at steady state cornering looks pretty decent even with stock ARBs.

I'm not sure I follow your statement.

I don't track my car, but a lot of those folks do track their cars and even do time trials with minimal to no changes to set up.

<-- sees a thread he posted in almost 16 years ago.
closes laptop, goes for a walk.

- andrew

Let's consider two extremes.

If a car keeps doing circles around a skidpad, the grip can be optimized by picking some total roll stiffness, and optimizing camber for the amount of roll that given tires generate. Then the relative front/rear roll resistance can be changed to fine tune the balance.

At slalom, the car rolls left to right and back all the time. If transitions take a lot of time, camber changes all over the place. If the suspension settles quickly though, it can provide more consistent grip, and thus better times.

Different race tracks and different AutoX courses fall somewhere in between these two extremes, and possibly benefit from different approaches.

Sure, I also do the same. Doesn't mean that the same setup is necessarily optimal for both applications.

Personally I also use SX2 tires at the track that generate less grip than RE71R's I use for AutoX. I presume the "optimal" amount of total roll stiffness would be different for these different tires, even on the same course.