Does Kumho have a serious problem? Answer = No

[Bildon]

The rubber compound did permemantly change consistency after it blistered / tore away or whatever.
It never returned to the same state as it would have had it not separated from the cords and "balled up"

New tires arrived today. Will let you all know how I make out with the low presure, lower camber testing.

[Colin@KW_Suspensions]

I can understand some blistering and that type of thing from too much camber and improper tire pressures, but the "playdoh" type rubber consistency is baffling me. Other than an impurity in the rubber or some sort of chemical getting on the tire, I can't see how that is possible.

[JamesB]

Well not that I have seen that before, but you never know if the bonding agent they are using is having a bad reaction with too much heat in that area of the tire thus turning the normal blistered rubber into something mushy.

[gprodracer]

Not being an expert by any means, rubber does not "uncure" by excessive heat. It will melt, and turn "mushy" (sort of) but will harden back up when it cools back down. This will be interesting to follow up on, as I agree that this sounds more like some sort of "chemical" reaction, not one of just excessive heat buildup due to too much camber.

Please keep us posted!

Mark

[Bildon]

>> Please keep us posted!

OK so far the new V710s, while perilously close to the Corrado have shown no signs of fatigue or failure. :P
Will update you all after WGI.

[Bildon]

OK we finally were able to get out to another race on the Kumho V710s.

We followed Kumhos advice and lowered our pressures and camber settings.
The result was that we were able to run through the qualifying session (front row) and 90% of the race with no tire related problems. Temps were well within spec and the hot pressures stayed under 35 psi as instructed.

Unfortunately we suffered a transmission related failure due to damage from our wreck at WGI earlier in the year... so we didnt get any full race length data afterwards. But the tires appear to be fine outwardly.

We qualified the car in 2nd place, took the lead at then ran in 2nd place for 9 laps until trans broke. (see that report elswhere)

We will continue to keep our eye on these as we run the remaining races this year. Will update here if there is anything of interest to report.

[erlrich]

Bill - not challenging your findings, but it occurs to me that if indeed your first set was from a defective batch you would probably have had similar results this weekend, don't you think? I would like to ask, did you noticed any difference in the feel of the car with the new setup?

The reason I bring this up is that I ran the Labor Day double at Summit on a nearly new set of V710s (had run 6 - 7 laps for heat cycling back in July). I decided to go with the recommendations you had passed along from Rudy (even though I'm in a rwd car) and so droppped my starting pressures to 28f/30r (normally start around 34 with Toyos) and my front camber from almost -3 to around -1.5 degrees. I left rear camber at around -2, since it is a much bigger pain to adjust on my car.

I unfortunately had to miss qualifying, and so started the Sunday race from the back of the pack with an untested setup. Long story short, the tires held up fine but the handling suffered (although I was still almost a second faster than on Toyos). The car developed a nasty understeer thorugh T10 and just generally didn't feel as comfortable to drive. So for the Monday race I said wtf and went back to camber & pressures that were closer to what I had been running with the Toyos. Specifically, I upped starting pressures to 32f/33r and moved camber back to -2.75 degrees. The car felt much, much better, and the tires still looked fine at the end of the day.

Now obviously I didn't get the chance to do any real testing, and I know every car is different and will need to be set up differently to get the most out of these tires, so I will withold final judgement for the time being. But my gut is telling me that the problems you (and others) have had may be less a result of improper setup than other issues. I have already made plans to do the test day before MARRS IX, so I should have more conclusive data to base an opinion on after that.

[dj10]

Bill - not challenging your findings, but it occurs to me that if indeed your first set was from a defective batch you would probably have had similar results this weekend, don't you think? I would like to ask, did you noticed any difference in the feel of the car with the new setup?

The reason I bring this up is that I ran the Labor Day double at Summit on a nearly new set of V710s (had run 6 - 7 laps for heat cycling back in July). I decided to go with the recommendations you had passed along from Rudy (even though I'm in a rwd car) and so droppped my starting pressures to 28f/30r (normally start around 34 with Toyos) and my front camber from almost -3 to around -1.5 degrees. I left rear camber at around -2, since it is a much bigger pain to adjust on my car.

I unfortunately had to miss qualifying, and so started the Sunday race from the back of the pack with an untested setup. Long story short, the tires held up fine but the handling suffered (although I was still almost a second faster than on Toyos). The car developed a nasty understeer thorugh T10 and just generally didn't feel as comfortable to drive. So for the Monday race I said wtf and went back to camber & pressures that were closer to what I had been running with the Toyos. Specifically, I upped starting pressures to 32f/33r and moved camber back to -2.75 degrees. The car felt much, much better, and the tires still looked fine at the end of the day.

Now obviously I didn't get the chance to do any real testing, and I know every car is different and will need to be set up differently to get the most out of these tires, so I will withold final judgement for the time being. But my gut is telling me that the problems you (and others) have had may be less a result of improper setup than other issues. I have already made plans to do the test day before MARRS IX, so I should have more conclusive data to base an opinion on after that.

[/b]

You need to compare apples to apples. If your springs, shocks, sway bars are set for one setting of camber, and car in general you would need a good test day to change setting to compare the things you are talking about with the tires. Doing it on a race weekend would not be what I would call a good test. IMO

Good luck

[Zneed4speed]

Hey Bill,

Please send me Rudy's contact info. My car started to wiggle under braking at Roebling Road a couple of weeks ago and my crew spotted a weird looking tire. It looks like it is de-laminateing--if there is such a thing.
Not nearly so bad as yours, but we caught it early.
The tires have about 5 track sessions on them. I had heat cycled them once then ran them a couple of months later for 4 sessions when the problem occured. PSI is good but I do run more camber than Rudy told you.

Thanks.

[erlrich]

Hey Bill,

Please send me Rudy's contact info. My car started to wiggle under braking at Roebling Road a couple of weeks ago and my crew spotted a weird looking tire. It looks like it is de-laminateing--if there is such a thing.
Not nearly so bad as yours, but we caught it early.
The tires have about 5 track sessions on them. I had heat cycled them once then ran them a couple of months later for 4 sessions when the problem occured. PSI is good but I do run more camber than Rudy told you.

Thanks. [/b]

Here are Rudy's phone and e-mail info:

1-330-670-2619
1-800-HI-KUMHO

RConsolacion @ mail.kumhotech.com (no spaces)

For what it's worth, I had almost the exact same failure as Bill (minus the gooey patch) at my last event at Summit Point in November. A patch about the size of my palm blew out in the center of the front left tire. Fortunately there was no catastrophic failure, in fact I didn't even realize it had happened until after I got back to the paddock and was checking over the tires. The tires were on their 6th heat cycle, and while I was running more front camber (2 3/4 degrees) and pressure (around 38 psi hot) than Rudy recommended to Bill I still think this is completely unacceptable. If Hoosier, Goodyear, Hankook, and Toyo can all get their tires to hold together under the less than perfect setup conditions many (most?) of us club racers subject them to, I see no reason why Kumho can't also.

Now that they have come out with a 225/45/15 I will be starting next year on Hankooks.

[charrbq]

Until this year, I've used Kumho Ecstas for enduro's and damp track situations and never had even a remote problem with them. Then Kumho quick making 13" so I had to change brands.

One thing I didn't notice...or maybe missed...was that no one checked or reported the DOT number on the side of the tires in question. They are "street" tires, so they've got to have one. This is an absolute must in tracking a tire's history. It tells the week of manufacture and the location of the plant...along with other things. Every manufacturer has the potential for mistakes, but the good ones, like Kumho, try to correct and to avoid them. But, there is a good chance that a raw materials supplier had a problem. This is not unheard of in the industry, but is more difficult to track. The tire manufacturer should get the info needed to track the production and the distribution of the tire, and this is best done through the DOT number. If they have the tires now, then I would assume they are doing/or have done that.

Contrary to what we might think, the making of a tire is an amazingly complicated process with tons of variables, anyone of which could cause a problem.

Also, Tire Rack is an excellent company that I've enjoyed doing business with for many years, but when it comes to diagnosing problems with the products they sell, you'd have a better chance at Walmart.

The Kumho rep should be commended for taking the time to listen and act in the manner that he did with the problem.

[philstireservice]

Just another bit of info on the Kumho V710......

Autocross sweet spot temperatures are ideally in the 140 - 150 degree area (in most cases)
Roadrace sweet spot temps ideally in the 180-200 degree area (in most cases)

Hoosier makes an A6 for autocross and a R6 for roadrace.....

Kumho makes one tire, one compound....V710.....

I should add that the Kumho V710 was the hot tire last year in autocross before Hoosier came out with the A6.

[iambhooper]

Performance wise, how do the Hankook's compare between the Khumo 710 and the Hoosier? Also, do they only pay contingency to the top overall finisher's in the group, or is it per class (like Khumo)? Khumo has an excellent contingency deal, yet I want to be on the safest most competetive product I can afford.

Those that are running Hoosier's on your ITC Honda's, what tire sizes are you running?

Thanks!