Time for new tires?

[exhilR8]

My original Pirelli P Zero tires have about 3000 miles on them, about 100 miles of which are from 4 1-hour track sessions. Below are a couple of pictures of the current state of wear. During my last track session, the grip seemed much less than I had expected, although the ambient temperatures were quite low (40 degrees f). I didn't measure the tire temperatures, although the grip hadn't gotten much better after about 15 hard laps. Since I'm a newby to performance cars and racetracks, any longevity extimates would be most welcome.

[desperado]

A couple of thoughts after looking at your photos:

1. You are not down to the wear-bars, so the tires don't need replacing yet IF you don't drive in wet weather. (In wet weather, the car is not very comfortable or safe when approaching only 2/32 inch of tread remaining.)

2. The extreme roughness of the tire surface is unusual in my experience. A couple of things come to mind:

• The asphalt at your local track might be unusually rough; do you know if it meets FIA specs?
• The one hour long sessions are very long. Most track day organizers run 20 minute to 30 minute sessions. The amount of heat you are putting into the tire in a one hour session, especially if you are running very hard, might cause the chunking which your tires are exhibiting along the edges of the grooves.
• Are you getting a lot of understeer or sliding the car a lot? If so, you may be overdriving the tires. The optimum slip angle for high performance tires is in the 4-8 degree range (depending on the internal construction and the rubber compound). Any more slip angle than that is heating the tire a lot more, but the amount of grip (g force) exerted by the tire actually goes down.

[exhilR8]

OK, thanks, I didn't realize that 1 hour sessions might be too much. I get to use the track exclusively for 2 1-hour sessions every month, so I have been trying to get the most out of my $797/year.

The asphalt at Sandia Motorsports seems totally normal, so I'm thinking it must be sessions that are too long with too much overdriving. I didn't start to feel much understeer until my third session, and by then the rubber was starting to come off in lentil-sized chunks. By that time, it seemd like the understeer would kick in at lower speeds/turning angles. I haven't been intentionally drifting, but it certainly has occurred while I've been exploring the limits of friction. But it does seem like the friction limits are a lot lower than they used to be with these tires.

I wonder if it's possible that I've "overcooked" the tires permanently...

[desperado]

I'm not an expert on heat cycling, but my understanding is that the softer compounds used on R-Compound tires are subject to heat cycling but that street tires typically are not. Here is an article on race tire longevity you might find interesting:
http://insideracingtechnology.com/tirebkexerpt3.htm

EDIT: Turns out I have this book on my bookshelf, but haven't gotten around to reading it yet. Nice to find the pertinent excerpt online!

[desperado]

OK, thanks, I didn't realize that 1 hour sessions might be too much.

It's like qualifying vs endurance racing. Driver's qualifying times are never equalled during the actual race. If they did, the tires wouldn't last for a full tank of gas. Same thing for your track sessions. If you stay out for an hour, you can't drive the car as hard as you could in a series of 20 minute sessions with an hour of cool-down time in between. (BTW, the same thing applies to the driver! I'm starting to lose concentration and make mistakes at the end of a thirty minute session, but 20 minutes feels too short.)

[exhilR8]

That was an excellent article you posted in the link http://insideracingtechnology.com/tirebkexerpt3.htm

It said "For most tires the first lap or two are the fastest laps those tires will ever produce....In fact you can see the tires give up during the two-lap qualifying runs for the Winston [now Nextel] Cup races. The first lap is almost always the quickest and many drivers just run one lap and go back into the paddock."

I guess it's an ironic punishment for my early exuberance that I now have to drive slower and slower each time. I guess I'll have more time in the paddock to contemplate how I'm going to take better care of my next set of tires. Maybe Michelin Pilot Sport Cup+/N-Spec...

[mngolfer]

But just think how much fun you had driving on the track every month for two hours with an annual cost of only $795.

Four 30 minute sessions would equal a longer smile and with some reflecting maybe allow you to improve your driving.

[exhilR8]

I certainly have had fun doing damage to those tires, and thankfully, no damage to the car.

I ordered a laser pyrometer to start measuring tire temperature during track sessions, and maybe I'll try using up my hour with two 15 minute sessions with a half-hour break in between. I'll have to experiment to see how quickly the tires can cool down.

I changed my avatar to reflect my excess of enthusiasm...

[Fashion Cat]

However unlike Jeremy, you don't find the V10 to carry an overtly serious attitude and the car can actually smile? Maybe at a joke in German.

[M3R8]

Use cooling spray on that rubber!

Actually it might not be a great idea.