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In at least two of this season's first five Cup races, excessive heat in the right-front wheel area has led to tire failures for several teams.
Those early-season incidents, and the fact that there are still many unknown variables associated with the new Generation-6 car, have created an air of uncertainty among teams.
With Martinsville up next on the schedule, has that awareness become a full-blown concern?
Greg Stucker, director of race tire sales for Goodyear, said he doesn't believe the number of melted bead issues this year has escalated significantly, "but it is definitely up."
Teams continue to learn about the new car, he said, and the trial-and-error process was likely behind the problems encountered at Phoenix and Bristol.
"We've had so many conversations with teams and with NASCAR about this particular issue, it's really down to the teams to try and make sure they are doing everything they can to get air to the front end, to get it to that wheel," Stucker said.
Martinsville is the smallest track on the Cup series at 0.526 miles and among the flattest with 0-degree banking on the straightaways and turns on both ends of the speedway banked at just 12 degrees. It has long been considered the most punishing on brake components and thus likely to produce soaring temperatures in the wheel area.
Cars reach speeds of approximately 120 mph on the two 800-foot long straightaways before slowing to nearly half that as drivers work their way through the nearly nonexistent banking in the turns.
Toss in stop-and-go, bumper-to-bumper traffic, repeat the whole process 500 times in a roughly three-and-a-half hour period and it's not unusual for brake rotor temperatures to reach nearly 1,400 degrees during the race.
In most cases, Cup teams go to great lengths to cool that radiant heat and vent it away from the wheel and tire. Hoses pull air in from the front of the car, fans blow air across the brakes and metal shields help direct the flow of the hot air as it is forced away from the rotor.
But when too much heat builds up, "it actually melts the nylon, the fabric that wraps around the bead of the tire," Stucker said.
"Of course, (the tire) eventually lets go."
The melting point of the nylon used in the tires is close to 400 degrees.
There are other factors at play as well. At Bristol, for example, increased speeds may have played a part in the increased number of melted beads.
The tires provided to teams were the same compound and construction as those used at the track approximately seven months earlier, however, lap times "were running about three-quarters of a second faster," Stucker said.
"So the lap times were significantly lower; the speeds were significantly higher than we had raced there in the past. I think that's a function of the new car, (it's) lighter. I heard guys talk about how much it got up off the corner that much better. You're carrying a lot more speed when you do -- obviously that generates more load; they have to get the car slowed down. It seems to be a different animal."
Stucker said Goodyear officials evaluated the tires that failed at Bristol off-site and later met with Hendrick officials to discuss �what had happened and what factors might have played a role in the incidents.
In Gordon's case, the team had made a two-tire stop, changing only left-side tires, prior to his incident. The right-side tires remained on the car for close to 150-160 laps. And during the stop, Stucker said, "that tire is sitting there on that wheel, and the rotor is radiating heat up through that wheel ? and it transmits heat to the tire itself."
Alan Gustafson, Gordon's crew chief, said he couldn't totally discount Goodyear's findings, but that the amount of time spent in the pit box prior to the tire problem was insignificant.
"I know our brake temperatures ? when you're talking Martinsville temperatures where you've got 1,300-degree rotors, 300-degree plus calipers, I maybe buy into it a little bit more," he said. "But I really have a hard time believing that that heat transfer ? we were stopped in our pit box; had a 5.40 (second) left side tire change. So we're in our pit box for five seconds. I have a hard time believing (it was a factor)."
Instead, he said he believed the increased speeds, which didn't fall off noticeably with a two-tire change, had more of an impact.
"You're stressing that (right-side) tire to a way higher extent. ? If you put on four, obviously the right sides are (out of the equation). If you take no tires, you don't have the grip to generate that kind of speed," he said. "So that, in my opinion, is where left-sides ? aggravate the situation."
Running lap times as fast or faster with fresh left-side tires creates "an extreme amount of abuse" for those on the right side, he said.
"Ultimately, is that what blew that tire out?" Gustafson asked. "I don't know. None of us are going to know."
Excessive brake heat shouldn't be a problem at Martinsville, he said, because the team already provides the maximum cooling allowed under NASCAR rules to cool the tire and brakes there.
"You can pound the brakes and pound the brakes and they're fine," he said. "They can live at these elevated temperatures and there will be no signs that you're generating excessive heat. Until you fail the tire.
"That's why I think you see a lot more blown beads than you had in the past, because the brakes can live at such a high temperature and have zero issue."
While the brakes have improved to the point that they are nearly bulletproof, can the tire withstand the increased abuse along with the constant 1,300-degree temperatures?
"In the past if you were going to hurt a tire, you'd know it because your brakes would fade or you'd have to pump your pedal, there were a lot of different signs," Gustafson said. "Well, the brakes don't have any issues now."
The heat at Martinsville will be an issue, said Trent Thomasson, on-site representative for Essex Parts Services Inc. Essex is the sole distributor for AP Racing Brake and Clutch Systems, and services approximately 30 Cup teams today. The bigger concern isn't brake failure, he said, it's tire management.
"I've seen 1,350-, approaching 1,400-degree (rotor) temperatures on a regular basis (at Martinsville) on a Saturday during a long practice run," Thomasson said. " ? Real time on the track (in race conditions), they get up there, 1,400 to 1,500 degrees in the corners.
"Today, the brake fluids, the pads, everything has been stepped up so what they see now, what they worry about now is the tire beads melting."
On bigger tracks that feature longer straightaways, the brakes have more time to cool. And because drivers use less brake, different packages, and venting to cool those packages, can be employed. Closing off a portion of the openings in front of the car allows teams to create more front-end downforce, something that's not worth the tradeoff at Martinsville where aerodynamics isn't as much of an issue.
Keeping the brakes cool, and extending the life of the tire, is more crucial.
The amount of camber a team chooses to run will also impact the life of the tire. Negative camber, where the top of the tire leans in toward the car, improves grip by providing a greater contact patch between the tire and the race surface and helps the car turn.
However, it also generates additional stress on the tire.
"Let's face it, race teams' jobs are to push the envelope on every part of the race car and that's what they try to do," Stucker said. "They just have a little bit different package to work with now and I think that's what they are trying to understand."
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