BROOKLYN, Mich. – With tires blistering and drivers expressing alternating signals of comfort and concern about 200 mph-plus laps, safety is taking center stage at Michigan International Speedway.  Jeff Gordon appreciates the need to be mindful of NASCAR's occupational hazards. But there's one option that the four-time Sprint Cup champion said shouldn't be considered: restrictor plates.  "It would be the worst racing we've ever had," Gordon said. "We'll go faster through the corners. It would be a huge mistake. I think Daytona (International Speedway) and Talladega (Superspeedway) are the only places that should ever have plates, and I question them there. So, we certainly don't want them here."  Vice president of competition Robin Pemberton said Thursday NASCAR wouldn't be implementing the plates, which are used to choke down horsepower and reduce speeds at Daytona and Talladega.  But after predictions that speeds would decline on the second consecutive day on the repaved 2-mile oval, they actually spiked in the final practice of the weekend.  Greg Biffle posted the fastest lap at 204.708 mph in his No. 16 Ford, and there were 14 drivers with laps exceeding 200 mph.  "The car was just really, really stuck to the ground," Biffle said. "It actually wasn't that hard to drive. It caught me off guard how fast the track was and how much grip there was. Maybe the heat is actually providing a certain amount of that grip. Normally it works in reverse."  So how fast is too fast? Biffle said he posted his lap in a setup specialized for qualifying, and he thought the race pace for Sunday's Quicken Loans 400 would be around 200 mph.  "I'm not worried about speeds for qualifying," said the Roush Fenway Racing driver, who led the Sprint Cup standings for three months before dipping to third last weekend. "The race pace isn't any faster than yesterday. I feel that's going to slow down some; we're well within where we were yesterday."  However, if the race pace were to increase, then so would the concern.  "It's right there on the edge of being too fast right now," Gordon said before Friday's first practice. "But too fast for what? For safety? We'll find out this weekend. Only time will tell. We're out there running single-car runs. Nobody has lost control or had any kind of a problem or failure, so at this point we're all good. But until that happens, we won't really know."  Greg Stucker, Goodyear director of race tire sales, said about a quarter of the 45 cars in practice experienced blistering — an excessive buildup of heat that causes the tread to degrade and separate (leaving a mark resembling a sunburn blister). Stucker said the blistering likely was a combination of several factors, including the speed and the track's new asphalt.  Friday's blistering prompted an 11th-hour change. Shortly before 9 p.m. ET Friday, NASCAR notified teams that it would be switching left-side tires for Sunday's race. A meeting of crew chiefs was scheduled for Saturday morning, and a 75-minute practice will be held after the Nationwide Series race.  The new tire will feature a tougher tread compound to help avoid the blistering Thursday and Friday. The compound tire was run at Charlotte Motor Speedway in 2006-07 after the track was repaved in 2005.  Goodyear is shipping in enough tires for teams to have 10 sets for the race, which is the original limit.  "With the new repave here at Michigan, coupled with the high temperatures we're seeing this weekend, we feel this change will help us put on the best race possible on Sunday," Pemberton said in a statement released by NASCAR.  On Twitter, Gordon had a positive reaction to the tire change: "I think it's a good move to go with harder left side tire. (It should) slow corner speed slightly and help tire blistering."  The prospect of tire problems had prompted the biggest concerns Friday. There were no incidents in 2 hours, 40 minutes of Cup practice Friday as cars approached 220 mph at the end of the straightaways.  "That is not that fast," three-time Cup champion Tony Stewart said. "We ran a lot faster in Indy cars. It's fast for stock cars … (but) the cars are stable even though we are running quick lap times. It seems like the longer we are doing it and the longer we are running these speeds, the slower it is starting to feel to us. It doesn't seem like it's a nervous 217."  While virtually all drivers expressed comfort in their cockpits, they also remained mindful of the danger.  "We don't feel bulletproof. Not at these speeds," Joe Gibbs Racing driver Denny Hamlin said. "You hate to think about what could happen, but running the speeds that we're running at the end of the straightaway, if someone gets turned the wrong way it could not be good going into Turn 1 or Turn 3, especially if you get turned in the right-rear.  "Anything can happen. We hope it's a safe race. At these speeds, we haven't tested (crashes) at these speeds."  Gordon said he was more concerned about the quality of Sunday's race (passing gets more difficult as speeds escalate) than with safety, but he acknowledged the issue deserved respect.  "I feel like our sport is extremely safe until something goes wrong," he said. "And it doesn't matter if you're going 220 mph or 150 mph. You don't want to hit anything. There's always that dangerous side everywhere we go. It's pretty cool that we're going that fast. The cars feel good. They're certainly stuck to the racetrack.  "But there's no doubt in the back of all of our minds, you don't want anything to go wrong at that speed, and that's part of racing."
Drivers say they're comfortable with their cars and predict speeds will fall during race, but excessive tire heat is prompting some concern.