Is an autocross compound and curb hopping bad?

[docs302]

Pocono TNiA yesterday. In all fairness these A7's are several years old but I keep them wrapped up and climate controlled during winter. They were still hanging in there. I was all over the left side curbs during session one and kept getting air over the same one. At the beginning of the second session lap two I dove into the fast, sweeping right hand turn 1 and suddenly was going straight off track. Very lucky the tire let go when it did. Wheel may have survived too.

I'm thinking failure from trauma? Pressure was 30 hot before I went out. No warning but I did notice I was pulling to the left before it happened. Anyone else running the A7 see this?

 

[blacksheep-1]

The "pull" that you experienced was most likely a loss of air pressure, as for the cause, sort of hard to tell at this point, but since you were using the curbs, it is a possibility. 30 psi was your hot pressure so you can bounce off curbs at that pressure without much risk, unless it was on an outlap and the pressure had not built up. It was lap 2, so it might have rolled over enough for the wheel rim to cut the tire.. stay off the curbs for the first 3 laps.
If the feel of the car suddenly changes, that's a good time to bring the car in for a look over, they don't magically fix themselves.
Oh, and BTW the A7 is not an autocross compound, there have been many..many SCCA and NASA national champs that run A7s regularly on road courses.

 

[docs302]

Oh, and BTW the A7 is not an autocross compound, there have been many..many SCCA and NASA national champs that run A7s regularly on road courses.

Yeah, should have termed it "ready-to-run-cold" compound or "autocross-like" compound.

 

[Dave_W]

BTW the A7 is not an autocross compound, there have been many..many SCCA and NASA national champs that run A7s regularly on road courses.

While road racers may use the A7, I doubt there are any autocrossers that use the R7.

Generally speaking, the A7 compound is designed to come to optimal grip quickly, and the R7 is designed to tolerate heat buildup from multiple laps without losing grip. What I saw from the TV coverage, the guys running A7s at the Runoffs employ the "run and hide" strategy of using the better "cold/warming" grip of the A7 to build a large lead, then pray that the guys on the R7s don't run them down & pass them when the A7s get hot and greasy and their lap times fall off. Drivers using this strategy fare better when they can drive very smoothly. Full course yellows also help a lot.

On a side note, I find it interesting that there isn't the same competition around the "R-compound" DOT-legal 0 treadwear autocross tire as there is for the 200TW autocross tires. Hoosier has had the market cornered for years.

 

[67GTA]

On a side note, I find it interesting that there isn't the same competition around the "R-compound" DOT-legal 0 treadwear autocross tire as there is for the 200TW autocross tires. Hoosier has had the market cornered for years.

Sounds like Hoosier is gearing up to challenge in the treaded tire arena early next year. I had a Hoosier rep ask me why I was using Goodyear 3R’s for the warmup session in NASA Time Trials. He said I won’t need them anymore come April, with the new tire being contingency eligible as well.

 

[blacksheep-1]

While road racers may use the A7, I doubt there are any autocrossers that use the R7.

Generally speaking, the A7 compound is designed to come to optimal grip quickly, and the R7 is designed to tolerate heat buildup from multiple laps without losing grip. What I saw from the TV coverage, the guys running A7s at the Runoffs employ the "run and hide" strategy of using the better "cold/warming" grip of the A7 to build a large lead, then pray that the guys on the R7s don't run them down & pass them when the A7s get hot and greasy and their lap times fall off. Drivers using this strategy fare better when they can drive very smoothly. Full course yellows also help a lot.

On a side note, I find it interesting that there isn't the same competition around the "R-compound" DOT-legal 0 treadwear autocross tire as there is for the 200TW autocross tires. Hoosier has had the market cornered for years.

I respectfully disagree, I've seen Aquilante, Bodle and other cut each others throats for an entire SCCA runoff race using A7s, as well as the rest of the top 5

 

[ajaquilante]

Pocono TNiA yesterday. In all fairness these A7's are several years old but I keep them wrapped up and climate controlled during winter. They were still hanging in there. I was all over the left side curbs during session one and kept getting air over the same one. At the beginning of the second session lap two I dove into the fast, sweeping right hand turn 1 and suddenly was going straight off track. Very lucky the tire let go when it did. Wheel may have survived too.

I'm thinking failure from trauma? Pressure was 30 hot before I went out. No warning but I did notice I was pulling to the left before it happened. Anyone else running the A7 see this?

Did you have vibration before failure? look around the tread for a puncture - maybe a slow leak - but usually that would just peel the tire off the bead. looks like it was cut/damaged. maybe damage on a curb is possible, but i can't think of a curb at pocono that you can' use far enough to drop a tire off the inside on the north/south layout i've used.

While road racers may use the A7, I doubt there are any autocrossers that use the R7.

Generally speaking, the A7 compound is designed to come to optimal grip quickly, and the R7 is designed to tolerate heat buildup from multiple laps without losing grip. What I saw from the TV coverage, the guys running A7s at the Runoffs employ the "run and hide" strategy of using the better "cold/warming" grip of the A7 to build a large lead, then pray that the guys on the R7s don't run them down & pass them when the A7s get hot and greasy and their lap times fall off. Drivers using this strategy fare better when they can drive very smoothly. Full course yellows also help a lot.

On a side note, I find it interesting that there isn't the same competition around the "R-compound" DOT-legal 0 treadwear autocross tire as there is for the 200TW autocross tires. Hoosier has had the market cornered for years.

The only class where the idea of the A's falling off comes into play is GT2 and that is because of the massive difference between the types of cars and tires. So much of it is setup and driving. Hoosier and I get a laugh out of the announcers and some competitors constantly banging on about waiting for the A's to fall off. So far I haven't been beat due to the tires yet. Much of that is setup and driving. You setup and drive to what you are using. Tire management is a fact of life on all racing tires from the perspective of driving and setup and the parts you use.

 

[Sam Strano]

A means autocross, R means road race. It isn't a secret that's what those letters mean, been that way back to A and R3S02s, 3's, 4's, 5's as well as a6/r6. Does not mean you can't track or road race A compound, as plenty have shown. But that wasn't their primary purpose in life.

Construction is also the same, compound only changes so if you want fast A. If you want more durable, R.

 

[Dave_W]

So if the A doesn't fall off for an entire Runoff sprint (given setup and driving style), I'd argue that Hoosier is holding out on the autocross community and could make the compound even stickier for sub-2 minute runs.

 

[blacksheep-1]

So if the A doesn't fall off for an entire Runoff sprint (given setup and driving style), I'd argue that Hoosier is holding out on the autocross community and could make the compound even stickier for sub-2 minute runs.

Try running drag radials at 50psi and see what happens.

 

[DaveW]

So if the A doesn't fall off for an entire Runoff sprint (given setup and driving style), I'd argue that Hoosier is holding out on the autocross community and could make the compound even stickier for sub-2 minute runs.

One can pretty easily overheat an A7 on an autocross course on a large car, 2 drivers, concrete. Not Yokohama levels of overheat but it is not uncommon to spray on 90 degree days.

I see this disparity on tire heat/wear a lot between track and autocross. Stuff that overheats at autocross, some people can track day all day. I think it is the violence and frequency of turns in autocross versus track. Driver skill and style is a factor on both types as well.

DaveW

 

[docs302]

Did you have vibration before failure? look around the tread for a puncture - maybe a slow leak - but usually that would just peel the tire off the bead. looks like it was cut/damaged. maybe damage on a curb is possible, but i can't think of a curb at pocono that you can' use far enough to drop a tire off the inside on the north/south layout i've used.

Not so much a vibration but I felt the wheel pulling hard to the left side right before it failed. After inspecting the carcass again I found a huge gash right smack in the middle of the tire so it looks like you are correct. Cut the tire, lost air and then high G turn did the rest. No harm so I am lucky. If that happened accelerating around the tunnel turn I would have hit the wall hard.

 

[Dave_W]

Stuff that overheats at autocross, some people can track day all day. I think it is the violence and frequency of turns in autocross versus track.

Yeah, very good point. Autocross is like taking a road course, shrinking all the corners to 1/2 or 1/4 the radius, then removing all the straights between them except one, and that you make into a slalom. Corner-for-corner, a road course turn may put more energy into a tire in one turn, but there's time for the tire to release that energy before the next turn. In autocross the tire doesn't get much chance to cool down between turns.

If you think of the tire like a brake rotor where braking & turning put energy into a tire like slowing the car puts energy into a rotor, on a road course you're applying the brakes and then releasing them so the rotor gets to cool down between turns; in the autocross version of the analogy you'd be riding the brakes the whole run, so the rotor just keeps getting hotter. Extending the analogy to think of brake pad compound like tire compound, on a road course you can have a pad that takes some time to get to working temp but can handle higher heat because you have the warmup lap(s), whereas in autocross you need a pad that can provide all its bite at (close to) ambient temp. But it also needs to keep working with that hotter rotor at the end of an a/x run. Tires getting overheated & greasy in autocross (or on the track) is like a "street" pad overheating into "pad fade" when used too hard.