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Old 09-23-2015, 03:58 PM   #1
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Tire Issues - Why?

Michelin Super Sports, approx 12K, plus 12 days of DE. They're chunking on the left frt. Had a DE last w/e. They looked OK on Sat (I checked b/c someone else with same tire had chunking issue). Was having trouble with tires hooking up on Sat, so experimented with lowering pressures. Eventually settled on 3 lbs less / tire (29f, 34r, both 3 less than recommended).

So with all that info, did the lower pressures cause my issue or was the tire maxxed out from too many DEs?

And I have 2 day DE at Kansas Speedway this weekend.





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Old 09-23-2015, 04:32 PM   #2
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what way does your track rotate? that might determine why you have more wear on left vs right. also, i think you are underpressure all around (i run 36/38 hot) - it 'looks' like you are rolling over onto your sidewalls, but i have no experience with supersports. perhaps try chalking them at the next event or a pyrometer?
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Old 09-23-2015, 05:43 PM   #3
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Last weekend's event was at my local track which goes clockwise.
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Old 09-23-2015, 05:51 PM   #4
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Is it this weekend like in a couple of days? I am trying to move a set of hankook RS-3 in 245/40/18 and 285/35/18 that turned out to be too tall in the front for my 986, I got them from a guy with a cayman. Dec 2013 production and about 50 autocross runs on them. I have them for sale locally for $300, I get a good rate on UPS, I bet I could have them there Friday for less than $100 shipping. I can get a real quote if you are interested.
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Old 09-23-2015, 07:01 PM   #5
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Thx for the offer but I'm on 19s
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Old 09-23-2015, 07:01 PM   #6
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It looks like you have insufficient negative camber, and are overheating the outer edge.
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Old 09-23-2015, 07:17 PM   #7
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Slow Down

I think you need to slow way down, you're messing-up your tires.
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Old 09-23-2015, 07:18 PM   #8
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my 2 cents for what its worth...

Your tires look very similar to the Ventus V12's I was running. The V12's while great street tires, and not great on the track. Probably similar with the Super Sports

You may have the tire pressures off a little
I posted a thread with a good formula to calculate tire pressure for a balanced car.
Weight on front and rear


I have also found that at the track the tires heat up pretty fast and get very hot and had to drop pressure a bit. That was before I had the formula and I started off at 30/36. I calculated 32 f and 34 r for the tires I have now 225/45-17 and 255/40-17

For the stock sizes it give you 32 front and 31.4 rear on 17's 204/255 f/r! On stock 18" 225 / 265 its 32 front and 33 rear.

Those are cold pressure, so once they get hot, you will probably need to bleed them a bit

As Porsche with the factory pressures builds in understeer, going with the calculated pressure, the car is more neutral. I would imagine with extra understeer, the tires will heat up more as you are pushing them in the corners
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Old 09-23-2015, 07:23 PM   #9
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Quote:
Originally Posted by LAP1DOUG View Post
It looks like you have insufficient negative camber, and are overheating the outer edge.
I agree. I had a set of Hankook Z214 do this -1.5 on front. When I went to -2 the next set seemed to stop the wear. I ran a advanced DE Unlimited track time that wear pattern stopped even running 45-50 minute sessions.
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Old 09-23-2015, 07:46 PM   #10
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Here is some good information on tire temp
Using a tire pyrometer-949 Racing
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Old 09-23-2015, 07:54 PM   #11
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clockwise track means more wear on the left tire which makes sense. there's chunking on the inside too, so i think more a tire pressure issue than camber. i do agree it's due to the edges heating - pyrometer would help you with that - but heating because of under-pressure. and you can't go by cold pressure at all; temp of track, air temp, length of session, etc., will all affect how much the tire heats = how much the pressure changes. i tend to consider my first session as a throw-away, just to get my tires to temp so i can semi-accurately get my pressures right. first thing at end of session should be pressure check - even before taking off your helmet. my fronts can go from 29 cold to 40 hot depending on temps and how stupid i am driving; sometimes only half that. fyi, planet 9 has a lot of chat about track tire pressures for the cayman and even specifically for the super sports.
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Old 09-23-2015, 11:33 PM   #12
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Those tires are about done. Agree that shoulders are overheating. If you haven't already, get a performance alignment while you are mounting fresh RE-71rs and target 36-38 psi hot for 19s. You are getting faster and the tires need more TLC.
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Old 09-24-2015, 06:22 AM   #13
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Quote:
Originally Posted by JayG View Post
Here is some good information on tire temp
Using a tire pyrometer-949 Racing
I love 949 Racing, my son has their wheels on his Miata.

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Old 09-24-2015, 09:19 AM   #14
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Those tires aren't "chunking", they are just worn out. Chunking normally occurs when there is thick tread, the tire overheats, and literally, chunks of rubber separate from the tire. That is one reason why most track tires have very little tread, or people get their tires shaved for track use.

Your tires just wore down through the outer layer of rubber, the base layer is exposed, and then the tread layer quickly starts wearing away exactly like is shown in your pictures. In no time at all you will wear through the base layer, and you'll see the cords showing. Once the tires are at the condition shown in the pictures, they are done-for, and are no longer safe. You can get more life out of your tires if swap them on the rims side-to-side, so that when the outside edge gets worn, you dismount and then remount them on the rim the other way, so that the worn part of the tire will now be on the inside edge.

As others have said, you need more negative camber to keep this from happening. You can also alter your driving style to try and minimize this happening, but there is only so much you can compensate for.

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Old 09-25-2015, 09:39 AM   #15
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My experience would suggest the same as the other comments of not enough negative camber and the edge has overheated..of course that being dependent that the tyre edge was not already worn thin.

Do you know what camber you are running at the front?
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Old 09-25-2015, 04:57 PM   #16
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This would be a good time for you to go down to an 18" wheel if this is going to be your primary DE/autox car.
Every consideration favors the 18s over going another round on the 19s if you're putting in enough seat time to wear out expensive tires. You're going to need new tires either way. A nice set of forged wheels wil command good resale as well.
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Old 09-25-2015, 05:02 PM   #17
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12,000 miles AND 12 track days on a set of STREET tires?

They are fried. Over cooked. Done. Put a fork in 'em.
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Old 09-25-2015, 07:40 PM   #18
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Every consideration favors the 18s over going another round on the 19s if you're putting in enough seat time to wear out expensive tires.
The theory sounds good until you do the math. I just did a quick check on TireRack of 18s vs 19s - you'll save a whopping $100 on a set of Conti DWs and a whole $225 on MPSSs. It will cost $700-1000 to buy a set of 18s. My math skills say it will take at least 7 sets of Contis to break even, or 3 sets of MPSSs (which I won't be buying anymore).

Plus I already have a set of snow tires sitting in my meager 2 car garage. Another set would eat up more space. I'll probably dial up more camber in my next alignment but I'll have to keep it reasonable for daily driving. It would really suck to have dedicated track tires and the only mileage on them is track time and the edges wear out with lots of other tread left. I guess the good news with that is I'd pay for the conversion to 18s faster.

DEing is a slippery slope, esp if you continue to drive on the street. Hard to find the right amt of compromise between street and track.

I'm typing this from KC as I'll be driving Kansas Speedway tom and Sun. But not on these tires. Punkin is currently sitting on jack stands as I stole her tires to run on Sydney. It's good to have identical cars.
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Old 09-25-2015, 09:11 PM   #19
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The major advantage with 18s is a much wider tire choice, nearly unlimited. In 19" I would mount RE-11s for street/track duty. A much more track capable tire than Conti DW or Super Sport. JMHO
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Old 09-25-2015, 09:57 PM   #20
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^bingo. I really don't understand the push towards 19 and bigger on high performance sports cars.there's no advantage.

Run your 19s for winter. Get a tire tree for storage or mount on the wall of your garage.

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