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Post AutoX tire wear; input?

JustDSM

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This past Sunday I attended my 2nd ever AutoX event after my first event earlier this spring pre-COVID. My first event the car was brand new, bone stock, and I was brand new to driving anything even remotely sporty after a long hiatus from having fun with anything related to autos.

I'm hoping to get some input from those of you more seasoned coneheads about what my tires are telling me here.. I have my suspicions that I ran too low of a tire pressure..BUT I'd love to get some input from those with a little more experience.

Car Setup:

FRPP Track Dampers (F/R)
BMR Handling Springs (F/R)
Steeda Full Length Jacking Rails

Front:
Steeda Camber Plates
BMR Adjustable Sway Bar End Links
Steeda Tension Link Bearings
Steeda Lateral Links w/ Extended Ball Joints (Roll-center correction)
Steeda Bumpsteer Kit
FRPP/ARP Extended Wheel Studs
OP Mustang 25 & 20mm Hub-Centric Spacers

Rear:
Steeda IRS Subframe Support Braces
Steeda Subframe Alignment Kit
Steeda Subframe Bushing Support System
Steeda Rear Camber Adjustment Kit
BMR Rear Shock Mount
BMR "Premium" RLCA Bearing
BMR Adjustable Sway Bar End Links
FRPP Toe-Knuckle Bearings

Alignment:
Front: -2.7Âș Rear: -1.6Âș Camber
Caster: 7.1Âș L/R
Front: 0.00Âș Rear: 0.10Âș Toe
Thrust Angle: 0.00Âș

The course was FAST and FUN! With the course being as fast as it was, I was a little too aggressive and over drove the car quite a bit. The car was vastly improved from what I can remember from my first event in a stock car. I was much more comfortable driving the car at/near the limit which contributed to an inflated confidence to over drive the car. Surface is a rough and rocky covered asphalt. I understand it has the nickname "gravel pit" from the locals..

er20_10_lsp.jpg


So both sides are comparable in terms of wear, so I'm only going to post front and rear from the drivers side. Tires are Michelin PS4S in 305/30/19 Square setup on 19x11's. I know these aren't "track" tires so don't hound me too hard for having street rubber :) Tire pressures were 32psi front/rear hot.

Front tire:
IMG_0674.jpeg
IMG_0675.jpeg
IMG_0676.jpeg


Rear Tire:
IMG_0677.jpeg
IMG_0678.jpeg
IMG_0679.jpeg



Is the wear excessive and just a result of my overdriving the car? Was this a pressure issue? Lack of Camber? Any input welcome!

Results for those of you who stuck around: #39

Screen Shot 2020-11-10 at 4.55.32 PM.jpg


PAX results: 54th/127

https://autocross.com/er/2020results/cc20_10_pax.htm

IMG_7774.JPG
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kz

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I am not sure where you see excessive wear. There is basically none. If anything, you likely have (no offense meant) underdriven the car. There is some wear on the sidewall so pressure could be higher but you should be able to feel tire flex in the corners rather than try to figure out the sidewall wear.

FWIW 305/30 Rivals at ~32psi on the front flex way too much (for me - on Perry's pics you can see it almost coming off the rim), I'm running 34.5ish.

Look at front left on this pics (sorry for pasting in the entire pic, don't feel like cropping the tire out) - this is probably ~34 psi.

kzielinski-5.jpg
 
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JustDSM

JustDSM

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I am not sure where you see excessive wear. There is basically none. If anything, you likely have (no offense meant) underdriven the car. There is some wear on the sidewall so pressure could be higher but you should be able to feel tire flex in the corners rather than try to figure out the sidewall wear.

FWIW 305/30 Rivals at ~32psi on the front flex way too much (for me - on Perry's pics you can see it almost coming off the rim), I'm running 34.5ish.

Look at front left on this pics (sorry for pasting in the entire pic, don't feel like cropping the tire out) - this is probably ~34 psi.
In hindsight, I think the "excessive wear" mention was the wear observed on the outside edge relative to the wear across the rest of the tire. It looks like I hammered the outer edge and didn't use much else of the tire. It is my hope to understand if this was a result of the pressures I ran, car setup, or my driving.

No offense taken! :) I'm pretty new to this stuff (it was only my 2nd ever AutoX) so it would not be out of the question to have my observations be completely opposite of reality! I do know that I entered the slalom at corner #2 quite hot and had to scrub a TON of speed by over correcting to get the car back on course. Same story to a lesser extend the 3rd gate in corner #3 was something I often overshot due to carrying too much speed on entry (or rather not setting the car up appropriately for the next gate).

I can see exactly what you're mentioning in your pic. I suspect from your picture and the pressures that was with, I was grossly under pressure. I appreciate you taking a moment to share your input!

Next event is the 22nd. I'll certainly experiment a little more with some added pressure in them.
 
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Dana Pants

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Probably somewhere between 34 and 36 psi front is correct. Use your hand to feel if the outside of the tire is significantly hotter than the middle, if so, add air.
 

strengthrehab

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Are these pressures y'all are talking about hot or cold?
 

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Dana Pants

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At least for me it’s the same pressure every run.

the last two events I drove a CS and a STS Miata and it was so nice to not do a damn thing between runs. They put less heat into the tires so the pressures are actually stable to within a few psi.
 

strengthrehab

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At least for me it’s the same pressure every run.

the last two events I drove a CS and a STS Miata and it was so nice to not do a damn thing between runs. They put less heat into the tires so the pressures are actually stable to within a few psi.
My question is:

Are you folks measuring the pressure with the tire cold (pre-run) or hot (at the end of a run?)
 

NightmareMoon

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They’re talking hot pressures.

Shoulder wear looks pretty good to me. You scrubbed down to about the right place on the sidewall. Might use slightly more psi but its a decent wear pattern. I’d start with the same 32 hot next time out and then after 2 or 3 runs increase it to 34 hot and see if it feels better to the seat of the pants.

IIRC I try to keep it between 34 and 36 psi hot with MP4S when I run those hard. 37 too high, 32-33 too low. (285/35R19 tho)

Keep in mind the shoulders are going to look a bit tore up from what you’re used to. Its the nature of handling courses, autox or track. Also the two types of rubber Michelin uses on the surface of the tire, the shoulders are a different compound that most of the middle and inside of the tire, they’ll respond to heat and abuse a little differently.
 

EFI

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I don't really see anything out of the ordinary, and you're certainly not going to get massive wear on P4Ss after a few short autox runs.
 

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SteveW

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That 305 is really wide for the size according to the Tire Rack specs. It will be hard to keep from killing the outside edges no matter what you did given it is actually pinched on an 11" wide wheel. More camber and a little bit more tire pressure would help.
 

DickR

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FYI according to some highly qualified autocross tire experts as good as the PS4S tire is unfortunately is it NOT good at resisting tire edge wear. The sidewalls are just not "stiff" enough to resist the "roll over" forces of dry pavement autocrossing like RE-71Rs, Rivals, etc.
 

Dana Pants

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That 305 is really wide for the size according to the Tire Rack specs. It will be hard to keep from killing the outside edges no matter what you did given it is actually pinched on an 11" wide wheel. More camber and a little bit more tire pressure would help.
I’m currently running 275 40 on a. 9 inch wide rim and need 39 psi.... so yep
FYI according to some highly qualified autocross tire experts as good as the PS4S tire is unfortunately is it NOT good at resisting tire edge wear. The sidewalls are just not "stiff" enough to resist the "roll over" forces of dry pavement autocrossing like RE-71Rs, Rivals, etc.
yeah it’s bad as an autocross tire, but the root cause is probably compound and carcas shape. I’m running the Yokohamas A052 now, and it’s the softest sidewall I’ve ever met, but damn are they fast.
 

kz

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yeah it’s bad as an autocross tire, but the root cause is probably compound and carcas shape. I’m running the Yokohamas A052 now, and it’s the softest sidewall I’ve ever met, but damn are they fast.
I'm inclined to try Yokohamas next year because I hate money. Have a choice of 295/35 and 295/30 and do not see any drawbacks of the 35 one other than sidewall flex - am I missing something (since you have the experienced with 18" wheels and now Yokos ;-) ) ?

Shorter one will impact gearing and I have been on the limiter (72 mph) on two national courses this year and very last local (which is scary given the lot size).
 

Dana Pants

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I'm inclined to try Yokohamas next year because I hate money. Have a choice of 295/35 and 295/30 and do not see any drawbacks of the 35 one other than sidewall flex - am I missing something (since you have the experienced with 18" wheels and now Yokos ;-) ) ?

Shorter one will impact gearing and I have been on the limiter (72 mph) on two national courses this year and very last local (which is scary given the lot size).
why not the 315 30 R18?

I see no reason not to go for the taller 295. In my experience, with the 39 psi the tire is plenty stiff...

they mount so easy I’m tempted to try the 295 on a 9 inch rim just to see what happens. (I probably won’t actually do this)
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