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Odd Tire Wear problem -Kumhos Ecstas

 
Old 09-28-2002, 08:35 PM
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RJay
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Post Odd Tire Wear problem -Kumhos Ecstas

Hi all! I've had a set of Ecstas on my car for about 6 autocrosses now and they'd been terrific up until this afternoons session. Setup for the afternoon was identical to the morning session, started 32/36 cold. After five morning runs, I started in the afternoon and the rear felt very twitchy. After the first run, I chalked it up to cold tires. After the second, I raised the rear pressure a couple of pounds. Nothing seemed to help. At the end of the day I examined the tires and the wear pattern on the tread was very odd. The fronts were fine. In the rear, the inner blocks seemed to be worn more than the outer and it almost seemed like the carass was cupped. OIn addition to the tire seemingly riding on the edges, the inner tread blocks were all worn at an angle, i.e. the side of the block closest to the outside of the car was lower than the side on the inside of the car, and all the inner blocks exhibited this wear pattern. Theres still plenty of tread (2/16"s or so) and the tires were heat cycled, but not shaved. I should mention this is a 2000 996 with 225/40, 285/30 18s.

So...has anyone else experiences this sort of wear pattern? Does anyone know what causes this sort of thing? Is this a tire defect or simply underpress/overpressure? I pointed this out to a couple of people at the event and they all seemed think the tires would quickly wear back to normal. Should I not worry about this for my next event or are the tires trash?
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Old 09-28-2002, 09:20 PM
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Bill Gregory
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I have Kumho Ecsta V700's (the DOT-R variety) and Kumho recommends roughly 35-40 hot. I normally run around 37-38 front hot and 38-39 rear hot. If you started at 36 cold and added a couple of more pounds, you could be in the mid-40's plus. Having done that once myself, the tires were twitchy at the mid-40's. The middle, inner wear you describe could be the result of overinflation.
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Old 09-28-2002, 11:26 PM
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Ed Newman
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I ran my set without too many problems, but a number of guys in the region have had problems with them going out of round, resulting in shaking, twitchyness and generally poor performance.
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Old 09-29-2002, 12:31 AM
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I measured the tire pressure after my third run...39.5 in the rear. It was a fairly cool day, in the 60's, an infrared pyrometer measure the surface temp at around 83. It was an extremely technical track. A lot of very tight corners, a skidpad loop, 3 very long slaloms (one was 7 cones spaced at 15 paces, maybe not hard in a Lotus but in a 996...whew...work!). All this tight craziness was followed by an 1/8 of mile straight (deep into 3rd gear), round a pivot and even longer straight on return, and then back into the tight stuff. FTD was a very well prepared 993 turbo on Hoosiers at around 1:40, with some times ranging to over 2 minutes. Point being it was a pretty wierd course and relatively long with a lot of rapid back and forth, could this have caused a problem?. My best early time was around a 1:43.5. In the after noon my best was 1:45.5...very disappointing. Blame it on the equipment eh? I'm going to the Zone 1 next week and I'm worried that I really need another set of rears before then. BTW are Kumhos dead when the tread blocks have worn off or do they still have some life after that?
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Old 09-29-2002, 07:03 AM
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RJay, sounds like you have a little too much toe-out on the rear wheels. Of the two alignment settings that could possibly produce the effect you have, camber and toe, the toe setting causes greater wear when it's out of spec. Add about 1/16" total toe-in and see how that works.
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Old 09-30-2002, 08:25 AM
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Thanks Danno! That makes a lot of sense, I'll have that done. Do you think the tires are shot, or might they wear back correctly after a run or two?
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Old 09-30-2002, 06:35 PM
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cfdarch
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RJay

I also have 6 autoX's on the Kuhmo Ecsta v700's and also have the the same strange wear pattern on all 4 Kumho's. It is quite pronounced. This problem is counter intuitive. I talked w/ another guy at an autoX yesterday and he's got it to. He referred to it as groove of death. It appears to be the tire and not the air pressure. BTW I have been running in the 35-40LB hot range. Was going to call Tire Rack today but by immobolizer system went down just prior to my 8th & final run yesterday. Dealer prognosis 2 bad computers from getting wet. A victim of Isadore last week. Keeping my fingers crossed on the ECU. Going to have to search the board for leaks <img src="graemlins/crying.gif" border="0" alt="[crying]" />
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Old 09-30-2002, 08:37 PM
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ARGH!!!! I was afraid of a tire defect. I've contact WheelEnhancement...sent them some photos, Hopefully something will happen. In the mean time it looks like I might have to spring for some Michelins...
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Old 10-01-2002, 07:58 AM
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Hmmm...lots of confusing opinions. Sent some photos to Dave over at Wheel Enhancement. He wrote:
[quote]Ron, from your photos, this looks like camber wear. If all of your tires look like these two shots, I'd find out how much negative camber the alignment was set at. This is definitely not tire pressure, it could possibly be excessive toe-in but you'd normally see scrubbing across the entire surface of the tire. The reason you see uneven wear across the face of each tread element is that the edges flex downward under load and don't wear as fast as the rest of the element. Please let me know what your suspension shop says after you have had a chance to talk to them. If you leave the camber as is, you can dismount the tires and swap them to the opposite side so you can "even" out the wear. Please let me know if you have any questions.
<hr></blockquote>

In any case, I had forgotten about the exchanging the tires from side to side trick, so as I don't have enough time to have the camber etc. checked out before my next event, I'm going to switch sides on the the tires. Thought others with this problem might benefit from this as well. Beats buying another pair!
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