dave968M3

I drove the DE at the Roebling Road PCA club race this wk-end in my 968 with Leda shocks, Racers Edge suspension upgrades, springs 800 lbs front/700 lbs rear, and new LSD. I had fun until my last run when I noted a decided wobble/shake in my steering. I pulled in and found a 12 in bulge on the inside tire wall of my L front Kumho Ecsta V710. The tires were new and heat cycled by Tirerack at the start of my day. I had the tire removed from the wheel and found the tire wall was "fatigued" per the Bob Woodman tire tech, as seen from the inside of my tire the tire had almost disintegrated at the junction of the sidewall and tread, it was thin to the point of nearly rupturing- thus causing the outside sidewall to balloon outwards.
I was very careful and started at 25 lbs cold inflation pressure and my first check after 8 laps showed a hot inflation pressure of 32 lbs, the next 3 runs the hot inflation pressures at the end of sessions were 33-35 lbs. The tired failed on my 5th run of the day.
The only other variable is my alignment, set at front -3.2 camber, 7.0 caster, -.10 toe and rear -2.7 camber and 0 toe.
???Could the front -3.4 camber have caused the tire failure. Kumho recommends camber -0.5 to -1.5, since "the tread profile of the Ectsa V710 is very round , the shoulder area must be allowed to work properly, allowing the tire to roll over onto the shoulder area by reducing the amount of negative camber".
I did have the other 3 tires dismounted and all 3 were fine, no fatigue or defects were seen, so it was only one tire that failed.
txs
Dave

fly2low

saw the same thing happen to a friend with same tires. Rather impressive - and scary

srf506

Were you banging the curbs? Unless there's a mfg defect in the tire that's the only other thing I can think of. Roebling is actually kind of benign on tires as I recall.

pat056

I've run 710's for 3 years without incident. I know when they 1st came out 5+ years ago the had some issue and I think actually recalled/replaced some of the tires.
Also, some of my BMW friends have spoken of abnormal LF tire problems at Roebling.
I would contact Randy or someone at Kuhmo and send them pics of the tire. Maybe even ask if they want you to send the tire.
That is rather unnerving. As far as Roebling. I ran 710's there in the race this w/e and the only issue I have at Roebling is increased overall tire wear. it's not as bad as it used to be prior to repaving, but it's still noticable.

Jim Michaels

I've had no direct personal experience with the V710, but they call for surprizingly little negative camber (-.5 to -1.5), at least compared to most other R-comps. Thus, your -3.2 degrees may be too much, which you're wondering about too. One can also get V-710s pretty hot on track, but I wouldn't think you'd have gotten them beyond the 220 degrees at the top of the optimum range. Those two self-inflicted contributions stand out in my mind, plus the possibility of a manufacturing weakness contributing.

BTW, thanks for not immediately placing the full blame on Kumho, as is the natural tendancy, it seems. Your approach of learning about possible contributing factors is not only more helpful, it shows more class.

randall951

Hey Dave;
I'm running a 951 in DEs & Club Racing (run in GT-3S class) with an almost identical set-up; typically running -3.5 front & -3.0 rear camber & alternate between the V710s & Hoosier R6s without issue. The only thing that caught my eye is the 25lb. cold start; I know a lot of the boys run that short but I don't. Typically start at 27 to 29lb depending on ambient temps etc., normally coming in around 35 to 37 hot.
So far so good....

What are your tire & rims sizes & at what vehicle/wet/driver weight combo??

Randall

dave968M3

Randall-
My wheels are 8.5inx18in front with a 245x35x18 tire and 10inx18in rear with a 285x30x18in rear tire
-Dave

dave968M3

Randall-
and my car +driver weighs 3150 lbs
-Dave

lowside67

Just a note re: camber.

My experience is with autox so take it with a grain in salt, but I have run several sets of 710s and the consensus in the BMW side of the world is we run these tires with between -3 and -3.5 degrees of front camber and 1 degree less in the back. I cant imagine running -3.2 camber being an immediate source of the problem. We had a guy locally who for lack of a better term got a "bad batch" of tires that after a very short amount of time developed tremendously bad cracks, and a big bulge. Kumho bought them back to cut open and see what happened. Perhaps you got a bad tire?

randall951

Looks like your setup is normal...I'd guess you just got a bad single tire, Murphys Law scenario....
Pats' idea of chatting with the guys at Kumho to see if they want a look at the tire is probably the best idea for a little peace of mind feedback...
I've seen 'bad' tires in every brand known at one time or another over the years...not that it is any consolation but...lol
Best bet is to inspect between each session to catch problems early on....

Randall

Professor Helmüt Tester

I've had failures similar to the one you described with BFG/Yok/Bridgestone/Kumho/Goodyear/etc. race tires over the years. Causes usually can be attributed to 1.) defective tire, which happens from time to time or 2.) curb-hopping/hitting stuff, which also happens from time to time.

Talk to Rudy or Jay or Mike at the Kumho Tech Center. They're all active racers themselves, and they'd probably like to talk to you.

mkd944

Roebling is actually very tough on Left Front tires. A short 9-turn track with only 2 left turns. The left front gets a lot of loading. I have ruined many left front Kumhos there also. You can swap L to R to try to distribute the wear but the left front is going to get abused no matter what you do. It was actually worse before they repaved last year.

Bill L Seifert

I had a sidewall failure on a 710 at Memphis Motorsports Park, and went off in turn one. I did not know it until then, but there is a gravel trap there. I made my oil cooler like a banana. I thought I had a puncture, now I am not so sure. The sidewalls stayed on the Fuchs wheel, but the tread went byby. Mine were 215-40-16's. I bought a new one, and ran a Putnam a few months later with no problem. I have not put them on since, because of an engine problem, but I still have the tires. I may try them at a DE.

Bill Seifert

1987 944S Race Car