BROOKLYN, Mich. -- NASCAR and Goodyear officials are switching the left-side tires and calling a special 6 p.m. Saturday practice due to concerns with tire blistering created by the higher-than-expected speeds on the newly repaved Michigan International Speedway. However, drivers will still qualify with the tires they've been using.
"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," said Robin Pemberton, NASCAR vice president of competition.
Fourteen Sprint Cup drivers topped 200 mph during Friday's final practice, led by Greg Biffle at 204.708 mph.
Goodyear's Greg Stucker said approximately a quarter of the 45 teams had issues with blistering, caused by excessive heat buildup that causes the tread to separate. That creates the potential for blowouts on long runs.
With lap speeds at more than 200 mph for the first time at a non-restrictor plate track, that creates a safety issue.
As a precaution, Goodyear offered teams race-day tires to scuff -- make a run on them to get wear -- which typically toughens the rubber and makes the tire more heat resistant. Stucker said many teams took advantage of the offer.
Biffle said his fastest lap was on scuffed tires, noting he likely would use those on race day.
"These are things that come along with a repave,'' Stucker said.
Biffle said he was comfortable with the speed a day after saying it was close to being dangerous by clocking 218 mph on the straightaway entering Turn 1.
"I thought it was [dangerously close], but not yet,'' said Biffle, estimating he reached 220 mph on his fastest lap. "I keep creeping up on it.''
Pemberton said Thursday he expected speeds to get slower as the track rubbered in and the temperature rose.
Instead they got faster. Tony Stewart's top lap on Thursday of 201.896 mph was topped by nearly 3 mph. Twice the number of drivers topped 200 mph in Friday's final practice than did on Thursday.
"It caught me off guard how fast the track was and how much grip it has right now,'' Biffle said. "Quite frankly, maybe the heat -- it is pretty damn hot out there -- maybe the heat is actually providing a certain amount of that grip.
"Normally it works in reverse. It could be the surface and the tire combination."