Tire Degradation & Data

[GSpeed]

We've run nine hard, hot sessions on our RE71Rs (245/40R17) over the past month or so. Here's a graph showing lateral acceleration and speed:



Blue- Yesterday’s second morning session. 1:27.2
Orange- July 30th morning session. 1:26.4. RE71Rs & Tarmac 2s
Green- July 18th morning session. 1:28.1. RE71Rs & stock suspension

Track temps were within a few degrees of each other, so we can consider that a constant. Given the setup changes, the Blue session should have been noticeably faster than the other two sessions, but it wasn't. Why? We simply were not developing the lateral load that we had been in previous sessions. The RE71Rs are still soft, and have about 4/32nds left (rough average). But the grip just isn't there.



Here's the IR tire temps of those same laps. The blue session was as warm as the orange session, with the exception of the big sweeper at the end of the lap where the orange temps got much hotter. I can't help but wonder if we wouldn't see the same thing on the left tires through that shorter sweeper a few turns earlier where the grip was noticeably higher.

You'd think the tire temps would get hotter as they dropped off, but it appears here that the temps aren't getting as high. It looks like since there's more sliding friction and less static friction, the specific µ is lower, the force being imparted on the wheels is lower (evidenced by the lower lateral acceleration), so less work is being done. That plateau through that last corner might be a visual representation of the limit of the tires.

Anyone have any input?

[strat61caster]

They heat cycled out, there's only so much heat and deformation rubber can take before it loses it's desirable properties. A lighter lower powered car will put less heat and therefore less wear into the tire compound than a heavier or more powerful car, racing karts the upper classes only got 1-2 days out of a set of tires, the novice groups could run the same tire for a whole year. Not sure what kind of input you're looking for?

Tire science is probably the last black magic art of racing. I remember talking about the hysteresis of rubber and trying to determine it's life but googling wasn't helpful.

It would be helpful for the rest of us if we could understand what you mean by "9 sessions" before noticing a dropoff in grip, we talking 9 track days of 100 minutes on track or 9 20 minute sessions. I know I'm not the only one considering RE71R's for next year but the reports of short life makes me want to stick with a more durable "200TW" tire.

[CSG Mike]

How many laps do you do in a session, and what kind of temps are the tires seeing? Do you have any pyrometer data?

[GSpeed]

Originally Posted by strat61caster

They heat cycled out, there's only so much heat and deformation rubber can take before it loses it's desirable properties. A lighter lower powered car will put less heat and therefore less wear into the tire compound than a heavier or more powerful car, racing karts the upper classes only got 1-2 days out of a set of tires, the novice groups could run the same tire for a whole year. Not sure what kind of input you're looking for?

Tire science is probably the last black magic art of racing. I remember talking about the hysteresis of rubber and trying to determine it's life but googling wasn't helpful.

It would be helpful for the rest of us if we could understand what you mean by "9 sessions" before noticing a dropoff in grip, we talking 9 track days of 100 minutes on track or 9 20 minute sessions. I know I'm not the only one considering RE71R's for next year but the reports of short life makes me want to stick with a more durable "200TW" tire.

As far as what kind of input I'm looking for, I would love to hear someone else's thoughts on that plateau in temps at the last big corner, more specifically my theory relating to sliding vs. static friction. I've got some books on the way to hopefully provide some more insight on that behavior.

Regarding the hysteresis of rubber, my understanding is it's all extremely proprietary and compound specific. I think the only way for us to determine the "heat life" of these tires is anecdotal.

Originally Posted by CSG Mike

How many laps do you do in a session, and what kind of temps are the tires seeing? Do you have any pyrometer data?

Sessions range from 8-15 laps, max 25 minutes. When I get into the shop in a few hours, I'll post up some more detailed information about the session duration. I don't have pyrometer data for the last half dozen sessions.

Basically, I'm aware the tires are heat cycled out, but I'm trying to narrow in on the best way to confirm that with the IR data. If that plateau at the end is what I think it is, that's a clear sign that we reached the tractive limit of the tires much earlier than before.

[GSpeed]

July 10th, Session 1- 10 laps
July 10th, Session 2- 18 laps
July 18th, Session 1- 8 laps
July 30th, Session 1- 16 laps
July 31st, Session 1- 19 laps
July 31st, Session 2- 17 laps
Aug 7th, Session 1- 8 laps
Aug 7th, Session 2- 13 laps
Aug 7th, Session 3- 13 laps

Total laps- 122

[Alan]

I have 15 days of 3-4 sessions (20-30 mins) each on a set of Hankook RS3s and they are an absolute mess. I have four more days scheduled this year and will try to make it work. Finding a way to keep tires from heat cycling out (or at least slowing it), especially for us budget track day folks, would conquer the market. I guess the answer is cancel one weekend each year and use the money for a second set of tires.

This board should find a way to organize a tire exchange so non-track folks can use our heat cycled yet still plenty of tread track tires. They still work pretty well on the street.

[strat61caster]

Originally Posted by PST

As far as what kind of input I'm looking for, I would love to hear someone else's thoughts on that plateau in temps at the last big corner, more specifically my theory relating to sliding vs. static friction. I've got some books on the way to hopefully provide some more insight on that behavior.

Regarding the hysteresis of rubber, my understanding is it's all extremely proprietary and compound specific. I think the only way for us to determine the "heat life" of these tires is anecdotal.

Sessions range from 8-15 laps, max 25 minutes. When I get into the shop in a few hours, I'll post up some more detailed information about the session duration. I don't have pyrometer data for the last half dozen sessions.

Basically, I'm aware the tires are heat cycled out, but I'm trying to narrow in on the best way to confirm that with the IR data. If that plateau at the end is what I think it is, that's a clear sign that we reached the tractive limit of the tires much earlier than before.

I think you're not too far off with your hypothesis, however I would put it in a simpler frame of reference, consider a hard low grip tire. Under duress compared to a stickier grippier tire, the hard tire will flex less, heat up less, and do less work providing less cornering force.

As the sticky tire has heat cycled out and lost it's compliant grippy nature it has morphed into a harder less sticky tire more resistant to cornering forces and heating up like the sticky rubber was.

Under what mechanisms it does that, well you'd have to infiltrate a tire manufacturer's racing division or a privileged race team to get anymore insight than the books your ordering.

But it sounds like you're getting <100 quick laps which translates to <130 minutes of hard running out of RE71R, that's not even 2x track days for us regular folks...

[GSpeed]

Originally Posted by strat61caster

I think you're not too far off with your hypothesis, however I would put it in a simpler frame of reference, consider a hard low grip tire. Under duress compared to a stickier grippier tire, the hard tire will flex less, heat up less, and do less work providing less cornering force.

As the sticky tire has heat cycled out and lost it's compliant grippy nature it has morphed into a harder less sticky tire more resistant to cornering forces and heating up like the sticky rubber was.

Under what mechanisms it does that, well you'd have to infiltrate a tire manufacturer's racing division or a privileged race team to get anymore insight than the books your ordering.

But it sounds like you're getting <100 quick laps which translates to <130 minutes of hard running out of RE71R, that's not even 2x track days for us regular folks...

It would be REALLY interesting to see some temperature data on these tires, more than anything else. We routinely saw a second's worth of time lost between morning session and afternoon session based off grip alone. If someone were running these tires in a cooler climate, I doubt they'd kill them as fast as we did. We're probably doing them a disservice by running them this hard.

I feel like we're approaching the limit of what Bridgestone would share with us.

[solidONE]

I wanted to try these or the Rival-S. I think I'll stick with the RS3 Hankooks after seeing this.

[CSG Mike]

Originally Posted by PST

As far as what kind of input I'm looking for, I would love to hear someone else's thoughts on that plateau in temps at the last big corner, more specifically my theory relating to sliding vs. static friction. I've got some books on the way to hopefully provide some more insight on that behavior.

Regarding the hysteresis of rubber, my understanding is it's all extremely proprietary and compound specific. I think the only way for us to determine the "heat life" of these tires is anecdotal.



Sessions range from 8-15 laps, max 25 minutes. When I get into the shop in a few hours, I'll post up some more detailed information about the session duration. I don't have pyrometer data for the last half dozen sessions.

Basically, I'm aware the tires are heat cycled out, but I'm trying to narrow in on the best way to confirm that with the IR data. If that plateau at the end is what I think it is, that's a clear sign that we reached the tractive limit of the tires much earlier than before.

Typically tire temps will drop as they lose friction; while sliding generates friction, it's not as much as deformation under grip/light slip angle.

[GSpeed]

Originally Posted by solidONE

I wanted to try these or the Rival-S. I think I'll stick with the RS3 Hankooks after seeing this.

I would be hesitant to draw that conclusion from this data. It's very likely we would have destroyed either one of those tires, too. It's not like these tires aren't fast anymore, either. Keep in mind we're a second slower than we used to be, but that's still a full 4 seconds faster than stock.

[solidONE]

Originally Posted by PST

I would be hesitant to draw that conclusion from this data. It's very likely we would have destroyed either one of those tires, too. It's not like these tires aren't fast anymore, either. Keep in mind we're a second slower than we used to be, but that's still a full 4 seconds faster than stock.

But is it as fast as or faster than a similarly aged RS3 is the real question.

[GSpeed]

Originally Posted by solidONE

But is it as fast as or faster than a similarly aged RS3 is the real question.

I don't know, and to be blunt, that's not what we're trying to answer. We've got to focus on the fact we're testing the car, not the tires. So we'll be ordering another set of RE71Rs for this thing, and see how that affects the lap times with the current setup.

[solidONE]

^ looking forward to seeing what you guys find, and moar graphs.