See recent posts for updates.....
First off let me say that I'm not some paid Hankook or Hoosier driver...
Anyone who knows me, knows that I've been running Kumhos forever and that I have always been very happy with their tires. The cost to performance ratio combined with the regional Contingency program is hard to beat.
However, we recently had our first real bad experience with Kumho in all these years of running them and I'm posting this not to embarrass Kumho but to alert anyone out there to a potential problem. Even if it was a bad batch or an already addressed issue...this info should be in the public domain for safety reasons alone!
The Tires in Question:
Kumho V710, size 225/50-15
The markings on the tires are as follows:
K60, 1305, YA5B, DOTH2MP
Mounted on brand new 15x7" wheels and run on the FRONT only of our ITS Corrado.
Each front corner weight: about 870 lbs.
Springs ~900lb/in.
Cold Pressure ~28psi
Hot Pressure ~38-40psi
3* of camber
Temps as they came off track just prior to discovering the problem:
~180/170/175 << dont draw any conclusions about camber. (quick cool down lap but long pit lane.)
But they were not over 200*
They were mounted and balanced correctly (inside facing inwards) and were never dismounted and remounted.
So here is the story.
The tires were purchased with Kumho bucks from an ITB victory in summer of '05 and then stored in bags until late this Spring when they were mounted for use. They were fitted to the car to make sure there were no clearance issues and removed. At the same time some 205 Kumho V710 were purchased and were used without incident in the first tests of the year and the first race of this year at Nelson Ledges. Also some 225 Victoracers (older) were used in tests without issue.
Watkins Test
In late July at Watkins Glen we had these 2 V710 on the front during some of our runs on the Friday test day. They were stickers at the beginning of the day. Since we were working on rear brake bias problems and splitter/air damn issues we never got to running them hard for a prolonged period and were in and out of the pits a lot. I'd say we did about 3 sessions and a total of maybe 10-15 laps on them. They were not on the car for every session. While they never felt bad we did record a high 233* on the inner left and 210 on the inner right when checking the tire temps during the hottest part of the day. (came in hot, pit #1) 40 psi HOT, track temp 100+
Pulled the tires off the car and put them in the truck. Didnt notice any problem. (Didnt look for it)
We then ran 205 V710 rears and Hoosiers in the front for the race weekend.
Next event: BeaveRun.
Saturday the 225 V710 were mounted to the front and again 205 V710 were mounted in the back.
Session 1: We were bedding in new brakes and checking for problems with our recently repaired suspension. All was well. No hot laps were run.
Session 2: Was sunny and dry so we went for a good time. I had plans to do only a few laps, bring it in to do tire temps (needed data at this track) and then go out and do a few more laps. We did just that. temps were in the 180*s. However during that second session we nearly took out a number of cars in front of us when going into the hairpin, immediately upon applying the brakes the car locked it's tires and pitched sideways. I immediately knew this was not a driver mistake and that something was amiss so I brought the car in where the crew saw the damage to the tires and told me they were "blistered". This was odd as I had not been locking the fronts other than maybe once and even then it was a very fast lock and release...they were not dragged along the track.
Upon removing the tires we were VERY surprised to find that the tread of one of the tires had actually began to simply peel away from the belts. And in the case of both tires there were "stretch" marks along the shoulder of the tire like the tread was straining to tear away from the inner plys. Also each tire had a large patch of "rubber" that had chemically altered it's composition. Even though they tires had cooled to the point where they could be easily touched, both had a large area that was the consistency of "Playdoh". IOW, it felt as if it was no longer rubber but a VERY soft doughy material with no elasticity. It was literally as soft as a wet kitchen sponge.
These areas of altered rubber were not in the shape of a sqaure "flat spot", they were also not on the inner side where the 3* of camber would cuase a flat spot to be located. Nor were there marks in any sort of radial patter that would indicate rubbing on the fender liner or bumper cover. They were simply large "blobs" on the middle and outer middle of the tire as if cornering heat from underneath had caused this. << Total guess on my part.
Below are the photos of the tires as they appear today. The "Playdoh" areas have settled a bit and have less of the "cottage cheese" look than they did when warm. The pics do clearly show the perfectly good peice of rubber that peeled away on the one tire and the beginnings of what appear to be another imminent "peeling" on the other.
I will be showing this info to the Kumho engineers who I hope can tell me this is indicative of a bad batch they had. I had heard of V700 problems a year ago but I am not aware of any V710 problems.
More pics:
http://www.bildon.com/pub/KTire32.jpg
http://www.bildon.com/pub/KTire31.jpg
http://www.bildon.com/pub/KTire30.jpg
http://www.bildon.com/pub/KTire29.jpg
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