Goodyear will alter its tyre allocations for NASCAR Sprint Cup's race at Michigan following blistering issues during practice.
NASCAR officials have notified teams that a different left-side tyre will be tested during an additional 75-minute practice session on Saturday evening, following Cup qualifying and the Nationwide Series event.
Kevin Harvick first voiced his concern following Thursday's test session on the new surface of the two-mile track, where he experienced blistering on the left-side tyres. A number of teams faced the same issue, some also having problems with right-sides.
Tyre code D-4554 will be replaced following qualifying with D-4020, which features a harder compound, different construction and mould shape compared to the tyres teams have run so far. Cup teams will have 10 sets available for the race and an extra allocation for Saturday's practice.
"We decided this move was best to provide quality racing here on Sunday," said Greg Stucker, Goodyear's director of race tyres. "In collecting data and speaking with drivers and crew chiefs throughout the practice days, we had two choices to make.
"Our first option was to make the team's race sets available to them before practice on Friday and allow them the chance to [scrub] them, in order to run them through a heat cycle to increase heat resistance.
"We did that, but after all the practice sessions ended on Friday, we concluded the safer option was to go to our contingency plan and bring in the 4020s.
"This code has been run before under similar track conditions and we have full confidence that it will give drivers and teams the enough grip to run a great race on Sunday, while doing so in the safest possible manner. Safety is always our No. 1 concern, and by bringing this tyre here this weekend, we will accomplish that goal."
The original tyre selection made by Goodyear was the result of a test session that took place on early April, where five Sprint Cup teams ran through different combinations.
Although speeds were already high back then, reportedly around 198 mph average, they have increased considerably during practice this weekend, resulting in higher operating temperatures.
A new track record is expected to be set Saturday in qualifying, when teams will run the same tyre selection they have tested since Thursday, before switching over to the harder compound for the race.