carnut101

I have a 2003 z06 that ive had out on the track twice. it has Kumho Ecsta MX tires on it, 275/40r17 up front and 295/35/18 in the back. I got the new tires near the end of June. They had a tread depth of 9/16". The last day of June, I went to Willow Springs (a high speed track), and after the day the tires looked very worn but were only down to 7/16". August 14th, I went to Streets of Willow, which is a slower, more technical track. After that day, I was down to 4/16" front and 3/16" rear, but the tires looked nowhere near what it was the first time (only a couple of spots with gummed up rubber). Since I had the tires put on, between the two times at the track, and driving it every day, I've put around 2500-3000 miles on the tires.

Today, on my way home, some idiot managed to end up sideways right in front of me. I was going about 40mph and had 3-4 car-lengths to come to a stop after I reacted. The tires squealed and ABS kicked in. For some reason, it felt like the car just wasn't able to keep traction while braking hard as much as it used to. Now it could just have been the adrenaline of the moment that kept me from feeling the braking force, but it got me wondering: Has the heat from on-track use badly affected traction on my street tires, even though they are only a little bit past half-worn?

asp04

You have probably got used to the all-out braking capabilities of the track situation, with hot tires. You then witnessed the effects of a cold tire in an emergency situation. There is no comparison. Hot tires stick, cold tires slide.

c4cruiser

I just finished a track day at Portland (Oregon) Int'l Raceway with my 87 that runs Kumho Escta MX tires. Going in, the tires were at about 50% tread depth (they are 3 years old). I noticed after a couple laps, the tires didn't seem to be as stick as they had been at other events.

I seem to recall reading a post a couple of years ago about how the MX tire compound that provides the otherwise great traction, goes away after the tire has worn down 50-60%. Whether or not that's completely true I have not otherwise heard, but I definitely did not have the grip the tires started out with when new. They did get hot and did pick up lots of rubber from the track surface, but it was pretty easy to get the tires to brake loose with the throttle.

Cold tire temps like you see for street use won't react as quickly as hot tires like you see on the track so braking will probably not be as good.

johninar

I think what you experienced with the MXs is normal. As was said above "hot tires grip", and the "heat of the moment" of an emergency situation, are probably right on the money. The heat cycles may have affected overall performance of the tire.

I'm at the end of life on my MXs. They might have 2mm left in the center, and zip on the edges. They don't grip hot like they did new, but still grip pretty well for what they are. I just compensate my driving for the push in the turns.

They do still appear pretty normal when they are cold, although I don't drive them cold much, I suspect that I would have a similar experience as you did. I don't have a big budget for HPDEs and have to stretch my track dollars as far as possible.

I don't know if my rambling is any help, JMHO

carnut101

Alright, thanks. I just wanted to make sure I wasn't prematurely killing my tires with heat.

By the way, c4cruiser, I remember reading somewhere that there is a traction-enhancing chemical in high performance tires that seeps out over time. After 3 years, even if the tires have 100% tread, they are beyond their lifespan.

67 fastback

age, heat cycles & ozone~ all kill tires

varkwso

Age and heat cycles will kill a tire. I often have lots of tread left on a street tire long after its grip is gone when I use them on a dry track. I retire them to limited street use till I need the wheels for new tires. But I often throw away street tires with tread still left since they are downright scary to drive.

But I suspect yours is more of a case of cold tires with some heat cycling thrown in...

V8 Juice

Jeff,
I thought (from reading your descriptive tell-it-like-it-is posts) you drove on tires until the cords slapped the fender so bad it drowned out the brake squeal from rivets on worn out pads rubbing against the few places on the rotor not grooved out!!
Art

JDIllon

LOL!!!!!!!!!!!!!!!!!! Thats very good, ART.

varkwso

Art - there you go giving away all my speed secrets .... I must say it is well written though

I do drive track tires to the cord and brake pads to the backing plate - it is the Scottish heritage I have somewhere I believe. Street tires that are work hardened and old will make a believer out of you though. I did 720 degrees on track at T5 exit at Roebling when I took out the old Pilot Sports that came on the 99 FRC. No warning just loss of traction. No telling how old they were....I swapped to nearly wore out Hoosiers and I was back home again sliding all over the place and having a great time...


My friends - you guys always have my back

yellow01

I used to use MX's as a track tire, they grip great when newer and hot. After a certain number of heat cycles they do get hard and even when heated won't grip so much anymore. Unless you are really sliding around and wearing them out, they will get hard long before you loose all your tread.

Granted like the others said, they were probably not very warm in a standard driving situation, but I have personally experienced MXs outliving their grippiness after track duty.

mathia

I've gone through two sets of Kumho MXs, both sets saw 5 or 6 track days about 15k of street miles. I probably could have gotten some more days out of the second set but I switched to Z06 wheels, which I put Kumho MXs on.

The heat cycling hardens the rubber. I found with both sets even though there was tread left, the grip deteriorated so much I decided to replace them. I did find with the second set they had more grip when I got rid of them. I think that's because as I become a better driver I don't slide the car as much and so I don't overheat the tires. The Kumho grip well hot, but overheat them and they get greasy and lose traction. After they cool they are never as grippy.