Suspension mods to even out inside-outside tire wear...
 

Hello, I have what I hope is a simple question for the group.

First lets go over the car set up:

2016 Scion FR-S
TRD lowering springs F - 1.0" drop - 3.6k rate, R - 1.0" drop - 4.9k rate
Bridgestone RE71-R 245x40
Wheels RPF1 17x9
Camber bolts
Latest alignment numbers show aprox. -1.5 camber on all wheels
Stock (non-TRD) sway bars
Stock struts

Tire usage:

Tires replaced after 4,000 street miles and about 8 autocross events of 8-10 runs each (55-75 sec per run). Total autocross time about 1.5 hours.

Hot tire pressure 32-30 psi front, 30-28 psi back.

Tires were rotated once (front-back), never side to side (by unmounting)

Car feel balanced with a hint of understeer.

Question for the group is what suspension mods will even out the inside-outside tire wear shown in the pictures. I am assuming that an even tire wear will also give better grip and will make the tires last longer since the load will be distributed across a larger area.

The car is not used on track and it is not a daily driver so the goal is to optimize the suspension for autocross. I just got a set of new tires so now is a good time to do suspension mods that can improve how the tires will wear out.


The first two pictures below are front tires, third picture is back tire.

Any comments or suggestions are welcomed.

You need more front camber if you can get it. You would also benefit from rotating your tires side to side (remounting after about the first third of their wear).

At autox, with anything under about 3 degrees of negative camber in the front you'll get lots of outside shoulder wear (around 2 degrees in the rear seems to be enough).

If you are class limited to just the camber bolts (like in DS), you're pretty much out of luck. If you are prepping for STX or SSC you can get more camber and that'll help.

Camber plates are what you need (for the fronts).

Your parts are strange, looks like whoever you run with don't use SCCA classing.

Even at -3.5° of camber in front I wear a bit unevenly.

You're already in STX, cheap solution is to make sure you have two sets of camber bolts on the front struts and max 'em out, should be good for -2.5° or more which will be a noticeable improvement, a good shop should be able to maximize the camber with your equipment. Leave the rear at -1.5 or maybe increase to -2.0.

Stiffer swaybars can help but it's a bandaid. If you want to run up front in STX you'll need to get more than -3.5 and likely a more dedicated suspension setup. If you're not classing by SCCA and using some other local system you can explore options there but most build the car for SCCA, or fun.

At -4.5° of front camber, I also have slightly more outer wear on rough concrete. Similar hot pressures with same tire, tire size, and wheel width. If you're on asphalt, you may be able to get away with less than -4.5°.

Get as much camber as you can from camber bolts, and get the rest from camber plate adjustment up top. Also consider getting a camber plate that lets you get more caster.

Definitely need more camber on the front and maybe a touch more in the rear, but the rear doesn't need that much. Adding stiffer bars and springs and such will just add more load to the tire and make this worse.

SPC bolts & the 14mm strut bolts got me about 3.2-3.5 per side. Add in the camber plates and I can get over 7 degrees. I'm sitting at -4 and that seems to be a good balance between braking performance and contact patch use, without killing the inside of the tire.

You need more camber, and stock springs.

^^ Like mike said, get US TRD spring out.

Stock diameter springs, 245/40-17 on 17x9 +45 wheels (only offset for 17x9 rpf1), I'm very surprised you can get *any* camber from camber bolts! What's your clearance from wheel/tire to strut/springperch?

You'll need camber plates to get decent negative camber up front, but they'll take away bump travel. I'm suffering over minor bumps with camber plates and front lowered 1.25", front suspension bottoms out too easily. 1" lowered will be better but might still be an issue...

It helps to get camber plates that don't raise ride height (HVT, Raceseng, Ground Control, AST, KW, etc.).

In my camber plates which do not raise ride height (one of the ones you mentioned), the radial bearing does reduce available bump travel. With the factory setup, the middle of the spring perch where the bumpstop makes contact is offset ~10mm above where the spring seats. On most camber plates there is a radial bearing housed in the middle of the spring perch and the bumpstop contact is offset ~15mm *below* where the spring seats.

I'd estimate ~25mm lost travel before the bump stop makes contact *in addition* to the lost travel due to lowering.

Bummer. I'm guessing you have the Raceseng plates. Scratch that off the list.

Thanks all for the reply. In San Diego, CA I can attend two types of autocross events, the BMW club autox where my class is non-BMW (anything goes) and SCCA events where the aftermarket wheels put me in STX. In the SCCA SD region this class has several BRZ/86/FR-S so it is the best for competition.


The consensus is that I need about -2.5 to -3 camber in front and about -2.5 in the back to improve tire wear. To get that amount of camber in front I need camber plates. The downside is reduced suspension travel in the front and possibly rub from the TRD spring against the tire. (wheel is 9" wide, 35mm offset)

Is reduced travel and rub also a concern with coil overs? Aren't they designed for camber adjustment and aftermarket wheels?

You need more camber for even wear... SSC cars are getting up to -3 on bolts and eibach springs, and I think a different hole size on the konis. Smaller springs as most coilover packages have add clearance. Also, wheel offset and width matter on what you can get.


If you're serious about this, time to plan ahead a bit and figure out what is your next step.