Strange Tire Sidewall Deformation

[Mike Feinstein]

Both front tires exhibit a sidewall deformity that goes around the outer circumference of each tire. It's about 3/8" wide and is on a set of Khumo Victoracers with about 3 DE's use on them. I run them at about 28-29 psi cold / 35 psi hot. They are 225-50-16's on 7" Fuchs. I pulled them off and installed another identical set and finished the DE with no problems last weekend. My other set has no such deformity and the rears (245-45-16 on 9's) are also fine. Car is an 89 Carrera.

Any ideas? Are they safe for on-track driving? I'd hate to have a sidewall failure at 100 mph through the esses. Could be really ugly. Here's some pics:

[Victor]

Pressure too low?

[scottb]

Originally posted by Victor
Pressure too low?

Looks that way to me, too.

[Joe Bob]

Send the pics to Kumho.....ask them.

[Mike Feinstein]

Khumo recommends hot temps at 35-40 psi...I run them at about 35 hot on the front and about 37 on the rear. I spoke with others at the track who run them lower with no problems. Also, if they were run too low, there would be wear showing on the side of the edge blocks. In the top picture, you can see an arrow in the rubber that identifies the proper "rollover" wear. The arrow is unscratched indicating proper inflation.

I contacted Tirerack and e-mailed pictures earlier. Awaiting a reply. Will try to find Khumo and do the same.

[Mike Feinstein]

Ed,

No bubbles at all and the inside sidewall is fine.

[cstreit]

I run mine at 32 hot and don't have that problem. I bet you got a defective set. I'd write them or the seller and ask for replacements or, at a minimum, a discount on the next set.

[ischmitz]

You need to deinstall that VarioRam motor and ship it to me. It's too much power for the rubber

Seriously, I have never seen that but it looks like the sidewall got really hot for some reason. Maybe it was a defective set or pressure was too low.

BTW: I still love my exhasut. Your setup was the ticket.

Ingo

[Mike Feinstein]

Originally posted by ischmitz
You need to deinstall that VarioRam motor and ship it to me. It's too much power for the rubber

Always looking out for my best interest! What a pal!

Seriously...glad you're happy with the exhaust...now...prove you're a man and go melt those sidewalls!!!

[ischmitz]

Mike,

One more oilchange/valve adjustment and I am back in business. The motor just finished about 600 medium hard miles. Meanwhile, I sourced adjustable Koni's for the front, Carrera brakes and some other goodies that went on. So when I am back it's going to be meaner and leaner.

And sure, I always look out for my pals with some good advice

Take care,
Ingo

[Joe Bob]

Originally posted by ischmitz
Meanwhile, I sourced adjustable Koni's for the front, Carrera brakes and some other goodies that went on.

HAH....he stole them off the 914 race car...."sourced" my buttocks.....

[Bill Verburg]

I wouln't drive on those. Seems to me there was a rash of Kumhos w/ disintegrating sidewalls like that a few years back. As I recall the issue was related to air pressure or lack there of. Everyone blamed everyone else, very ugly and no satisfactory resolution that I ever heard of.

[masraum]

Hmm, looking at the pics it looks like you are really wearing the outside edge, but getting nearly no wear on the inside edge. Could be that alignment is a big part of the wear and sidewall issue. My guess is too little negative camber. You should be getting SOME where on the inside, but it looks like you're getting next to none.

About the tires I don't know if it is worth driving on them or not (I would definitely send the pics to Kumho), but I think I would check into why they are wearing like that.

[Mike Feinstein]

Steve,

Car has been recently aligned and cornerbalanced (following engine swap). Running 1.6 neg camber in the front. If you look at a new set of Victoracers, the treadblocks are much deeper on the inside. The outside almost looks bald when they're new. I've looked at many others and all seem to wear this way, so I think they are OK. I'll try to find a pic of new ones.

Bill, that's interesting. I wonder what the response from Tirerack/Khumo will be. Hmmmm.

[Mike Feinstein]

Here's a pic of new ones from their website.

[89911]

Whatever variables your running, I still think your tire pressures are too low, at least for the initial few runs until they heated up. Your using 16" tires also which will make for even more sidewall flexing. The area you indicated looks to be where that flexing point would be. Because it happened to both wheels, I would rule out defects. I've used Khumo for the last 3 years and one thing for sure is you will get plenty of opinions on what the right pressure is. The general consensus is 38-40 hot. If its not a hot day and you are jumping from a cold pressure of 28 to 35 and not driving the tires off the car, check out the front alignment also. You may have too much toe in or out.

[Mike Feinstein]

Just heard from Rudy at Khumo. He said my pressures are fine and he wants to see the tires to evaluate the problem. He offered to send me a new set right away along with return shipping papers to send these back to him. Can't ask for better service then that!

[Kevin Stewart]

yep Khumo recalls tons of these tires, Kevin

[CRH911S]

It's possible the sidewall ridge has something to do with ply overlap. It doesn't appear to be a low inflation condition. But I could be wrong. I recall seeing something similar but it was a start stop thing and not continuos as the picture indicates. I'd check with the manufacturer and if they can't answer then I'd remove tire just to be on the safe side.

[Kevin Stewart]

Serious the tires are recalled, Kevin