Joe Weinstein

Hi all. The tires have worn down to the wear bars in the big circumferential
grooves. Assuming even wear, are they near completely done or can I
continue to get stick with them till they go bald?
thanks in advance,
Joe Weinstein

Professor Helmüt Tester

You can run them until you see cloth, or all the air falls out. How much stick they have depends on how many heat cycles you've run them thru, rather than 'total rubber remaining'.

Joe Weinstein

thanks. Now, is there a minimum upper temperature that defines a heat cycle?
I understand that 20 minutes of track time is a heat cycle for sure. Is driving a
tire 50 miles on a freeway a heat cycle?
Joe

38D

You should ask yourself if it's worth crashing when a tire fails just to squeeze out a couple more laps.

Willard Bridgham 3

I quit using Kumhos when I ran them bald once and the tread belts separated way before I saw fabric.

It is reasonable to ask if you want to risk your safety as well as other's safety to save a few bucks.

If you crash or cause others to crash, the cost of a set of tires is infinitely small.

Joe Weinstein

I understand your concerns, and they are my fault for not saying my application
is autocross, not on-track mostly.
Joe

Professor Helmüt Tester

It may not be. Are you getting to the magic 170-180+ deg. F. range ? If not, your tires may not have noticed the event.

It's all about temperature. If you haven't gotten them hot, then probably not.

I'm comfortable in saying that I've driven more Kumho's down to the cords (or wires) than all of Rennlist combined, and can give as references to attest to that Rudy, Mike, Jay and the other Mike at the Kumho race tech center. If you don't run them down past the wear bars, you're throwing away good tire. Whe you bust a belt or run into the first layer of fabric, you'll know it. It is painfully obvious when the tire is 'done', and with a DOT race tire you still have a pretty good safety margin...good enough to get back to pit lane.

Anecdote: At a 24 Hour a bunch of years ago, we were having our usual set of tire woes...burning the fronts off about 5-15 minutes before we'd hit our fuel window (140hp fwd race car, it cords a set of tires every tank). Our usual mantra is "You can't come in until the car coughs", so some of those tires were really hosed by the time we'd finally pit (think 'wire brush'). We sent a guy down pit lane with a pair of binoculars, and had him watch the sunlight glint off the wire belts of the front tires as the car turned onto the front straight. When the 'shiny stuff' (wire belts, below the cloth layers) got to be ~25% of the tire width, we'd come it, regardless of fuel situation (damn....). Nobody crashed. Nobody lost control. Nobody hit anything. Extreme case ? Yes. Is there a message enclosed inside that extreme case ? Yes:

Throwing away tires just because the 'groves' are getting thin is a waste of tire, and a waste of money.

Joe Weinstein

gotcha. Much thanks! I am very impressed at the longevity and performance of
Kumho 710s in autocross. Hoosiers have a re-use life like kleenex in comparison.

Jim Clark

Great example of thriftiness or plain full utilization of a consumable..............How about multiple heat cycles? You covered endurance conditions but what about sprints? Did or do you utilize tire treatments or softeners to extend the grip so all the rubber was used? And if so, what kind? I have been ready a number of threads on this but information is available from a source such as you with the vast experience than that create good information and direction to follow. Thanks in advance for the help.