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Excessive tire wear on outside shoulder on track, 305/30/19, normal?

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Need some help: I've been running a 305/30/19 square setup on my '11 GT on track for a while now and it's been great except that I keep getting excessive tire wear on the outside shoulder. I'm trying to figure out if this is a setup issue, a driving issue, or just normal on an S197 with such wide tires.

Basic setup is Cortex coilovers, 400/200 spring rates, Eibach 35 mm front bar on middle position, 18 mm Ford rear sway (or no rear sway), Vorshlag front cc plates with 3 degrees neg camber. I've been running tires 35 psi hot all around, careful to check right away coming off track. Unsure of the exact ride height but car is sitting pretty high, not slammed at all. Using spacers and extended studs up front and rotating tires corner to corner/front to back between events.

Car feels good and balanced and overall easy to drive quickly but by now I have now gone through multiple sets of 305/30/19 tires and keep getting significantly more wear on the outside shoulders as compared to the rest of the tire. I've been mostly using RE71, GY SC3, and SC 3R. Tires keep turning blue on the outside shoulder, and some of the Goodyears have blistered. None of the tires have seemed to be rolling over excessively, based on indicators on the tire sidewall. It appears most of the excessive shoulder wear is coming from when tires are mounted on the front. Car does not seem to have excessive roll.

I am torn between maybe stiffening the front roll rate, on the theory that the front might be rolling over too much and losing suspension geometry, versus softening the front roll rate on the theory that the fronts are carrying too much of the cornering loads? Any other thoughts or ideas on things to try? Any experience, advice, or tips on this would be much appreciated, thanks all.
 
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1.) If you have the funds for it, a tire pyrometer would be a good investment. Have a buddy take your temps (Outside edge, middle, inside edge) during a hot lap. Here's the one I have used: Pyrometer kit. Thinking out loud here: if your theory of the shoulder rolling over is correct, then the more grippy of tire you run, the more temperature excess (in percentage vs. the inside temperature of the tire) you should see on the outside shoulder.

2.) You comment that as-is, the car is balanced. So I think anything you do with the sway bars will change (and potentially worsen) that balance. Just something to keep in mind.

3.) With 3r's, I think -3.0 might not be enough camber, especially given your front spring rate for that tire. As you have probably found out, 3r's are very, very grippy. The more grippy of a tire, the more camber you need, and the more spring rate you need to prevent the rollover you are experiencing. @67GTA what camber do you run?

4.) Are you gradually letting the tires get up to temperature? Going out on 26psi cold tires and then giving them everything you've got will result in sidewall rollover in my experience.
 
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Good thoughts, keep them coming please and thank you. Answers to your Qs:

Daily driver alignment is zero toe with cc plates in most upright position. When I go to track I move to max negative camber (-3 degrees) so I have some toe out but I don't know how much.

Max neg camber is 3 degrees, strut towers uncut.

Pyrometer is a good idea, I will get one.

Like you I was wondering if 400/200 might be too soft. No aero btw.

Yes, I try to bring the tires up to temp gradually. I usually over-inflate slightly and bleed them down to 35 psi after first session.
 
Big bars can be a big help to add roll stiffness with softer springs. I went to the BMR 38mm front bar to help with softer springs (originally had BMR Handling springs, now on H&R Race), and it has been very effective.

It will bring some push (BMR 38mm is big, stiff bar), which you will likely want to balance out with more rear bar (25mm Strano rear bar in my case), but I have been pretty happy with the compromise.
 
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you can also "chalk" the sidewall and see where it scrubs off, These cars love light springs and small sway bars, and you sound about right, I'm assuming these are just the front tires doing this, so maybe more camber or... if you have not thought of this, all the caster you can get, by doing this you will get something called "camber gain" as you turn the wheel into the corner, so max out the caster and see what happens. Be careful of over pressuring tires, manufacturers will always tell you to add PSI, but it is a crutch, yes it will stop some of the side wall deflection, but it will do so at the loss of traction. It can also send you down a rabbit hole, because more psi - less traction - more steering input - more rollover - more psi - less traction - more steering input - oh look my car pushes and the tires are corded kind of thing. It is death on a banked track. Anyway .. I gotta go, heading to Sebring in 5.
 

Bill Pemberton

0ld Ford Automotive Racing Terror
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One simple question I often ask is , " How often do you rotate your tires ?" There are tracks I have run that needed 4-5 switches a weekend because they loaded up one side so heavily , whereas there were others that might only need one or two changes. Just another thought to toss into the ring.
 
I would do a new baseline alignment check with focus on the toe at max camber. If it's towed way out that may be what's going on. It's going to be a give and take from street to track. I got lucky with my vorshlag setup and have maybe just a tad more outside wear and have not experienced any major understeer. I don't know if my numbers will help or not but here they are -
- Street -1.3 camber +0.03 toe, max caster.
- Track -3.0 camber - 0.12 toe, max caster.
No cutting required.
Ford progressive racing springs 1" drop

I chose negative track camber rather than positive because I am new and preferred more straight line stability. I didn't want any surprises going 130 down a straight.

Here's the thing with my setup. The first thing I had to do is mark with a paint marker where the middle of the strut bolt sits in relation to the tower for my street settings.

Don't mind the 2 small holes. I was thinking I could do a bump stop for the street setting but realized that was a bad idea. If I misspelled stuff or something I'm bad on a phone.
20230310_080216.jpg
 
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Thanks all. I'm trying to keep spring/bar rates as soft as possible provided suspension geometry remains correct. But good points about stickier and bigger tires maybe needing more spring rate?

How do people like my 400/200 spring rate and swaybar setup? Too soft, about right?

@blacksheep-1 interesting point about caster and camber gain, that is new info to me and I need to learn how that all works. I'll do some research.

@Bill Pemberton I'm not rotating them as often as you mention.... but I rotate often enough that by the end of their life all four tires are worn equally and all have this excessive wear on the outside shoulder. So I THINK I'm evening the tire wear out pretty well?

Toe out wouldn't cause wear on the outside shoulder of the tire, would it?

I'm currently at -3 degrees camber, does -4 with cutting the towers sound like a logical next step to try?


Appreciate the help and insights
 
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A little followup, @s9669s kindly took his comments offline but gave me some really great feedback that might be useful for others. After chatting with him a bit, looking at pictures of his tires, and thinking about my own driving, I think I've fallen back into a couple bad habits especially on turn entry on slow corners. First, I am pretty confident I am turning in too abruptly and inducing understeer and then second, I think I am reacting to that understeer by adding more steering input. I'm just over-driving (or mis-driving) these tires. I don't video but I am pretty sure this is my problem.

Driver error, imagine that. Will keep practicing. Thanks all.
 
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Thanks all. I'm trying to keep spring/bar rates as soft as possible provided suspension geometry remains correct. But good points about stickier and bigger tires maybe needing more spring rate?

How do people like my 400/200 spring rate and swaybar setup? Too soft, about right?

@blacksheep-1 interesting point about caster and camber gain, that is new info to me and I need to learn how that all works. I'll do some research.

@Bill Pemberton I'm not rotating them as often as you mention.... but I rotate often enough that by the end of their life all four tires are worn equally and all have this excessive wear on the outside shoulder. So I THINK I'm evening the tire wear out pretty well?

Toe out wouldn't cause wear on the outside shoulder of the tire, would it?

I'm currently at -3 degrees camber, does -4 with cutting the towers sound like a logical next step to try?


Appreciate the help and insights
I think you want to be cautious about combining a lot of negative camber with toe out. -4 is a lot, so maybe make a smaller adjustment. Also, I have not yet tried BS1’s suggestion to increase the caster, but that’s my next step.
 
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@67GTA what camber do you run?
I’m running 3.5ish on the same tire. Wear has been pretty even as long as I don’t get lazy with rotations.


First, I am pretty confident I am turning in too abruptly and inducing understeer and then second, I think I am reacting to that understeer by adding more steering input. I'm just over-driving (or mis-driving) these tires.
Are you trail braking at all? If not, it may help keep the outside front loaded up and resist understeer.
 
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I don't video but I found this view from another car at a BMW day this past fall. I'm the gray Mustang at 4:50. To me it doesn't seem like my car has excessive body roll but I'm not totally sure?
 
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I don't video but I found this view from another car at a BMW day this past fall. I'm the gray Mustang at 4:50. To me it doesn't seem like my car has excessive body roll but I'm not totally sure?
I had a 2011 GT and a 2014 GT500. Both handled well with about -3.4 degrees of front camber, which I got with Vorshlag plates and crash bolts. From the video, your car's stance looks good, so I don't think suspension mods will help, especially if the car's easy to drive as it is. What about brakes? Is it possible that your brake balance is "forward" and the front tires are doing more work than they should? I did a lot of reading about the development of the 2013/14 GT500 and someone from SVT had said in an interview that the ABS firmware had a brake balance change that shifted some of the brake loading from the front to the rear in Track mode. I always thought it was to improve handling, but it could have taken some load off the front tires as well, given the weight and forward weight balance of the GT500. It's just a guess, but, from the looks of your car, I don't think it's a suspension problem.
 
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I drive a 2014 Mustang GT and one of the things that helped my tire wear after all else that was explained here was getting the bump steer spot on, as well as a good 4 wheel string alignment.

My actual geometry would not be much help as I am running a Cortex SLA, but the commenters are on the mark as we have found those same things on my friends car that is running coil over strut suspension. The driving style comments are right on as well.

The bump steer has to be set with the bump steer kit and the bump steer gauge. Try borrowing one if you can. We have three of four of us that share those types of expensive tools. There are several write-ups on TMO, especially @Fabman. In order to do it correctly you have to take out the front springs and re-assemble everything so you can measure from ride height then in compression and extension. It will help handling as well as tire wear.

For the 4 wheel alignment, you will need adjustable rear LCA to get the rear square if necessary. We have corrected several of our track Mustangs. Again, a good tool to share among friends.
 

Dave_W

Cones - not just for ice cream
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Connecticut
I had "over-driving corner entry" in tire wear bingo, but didn't have time to post until now.

Remember, it's much easier to over-slow by 5% and then ease off the brakes early to maintain apex speed, than it is to under-slow by 5% and have to scrub speed between turn-in and apex. Try using your fingertips to hold the wheel to get better "feel" when you start to understeer (more nerves in the tips of fingers), or at least make sure you're not using a death grip on the wheel (pressure deadens the nerve feeling). Be smooth on your turn-in, try turning the wheel less but earlier for turn-in, then turn some more to the apex. You're making a parabola instead of a constant-radius arc.

Just back up your braking point a bit earlier, so you can be mostly off the brakes at turn-in, and keep a bit of trail-braking to apex. The primary goal of trail-braking is to keep a bit of weight on the nose, not to slow the car - that's a by-product. Get most of the braking done in a straight line.

And remember to have fun.
 
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What about brakes? Is it possible that your brake balance is "forward" and the front tires are doing more work than they should?
I have the usual 14" Boss 4 piston caliper setup in front and GT500 in rear, GLOC 12 front and 8 rear.
 
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I have the usual 14" Boss 4 piston caliper setup in front and GT500 in rear, GLOC 12 front and 8 rear.
Unfortunately, G-LOC doesn't show information about mu for their pads, so it's hard to know whether the bias is too far forward. But then, as @Dave_W said, trail braking takes a lot of load off the brakes and off the tires, so maybe give it a try to see if it helps.
 

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