Firestone to evaluate new IndyCar street course tyres in Sebring test

Based on feedback from drivers over several seasons, Firestone has sought to increase the gap in durability between its primary tyre and the softer alternate that offers more grip but has a higher rate of degradation.

The manufacturer has now committed to testing four different street course compounds with AJ Foyt Racing's Tony Kanaan and Graham Rahal (Rahal Letterman Lanigan Racing) at Sebring on February 26, as the new for 2018 aerokit is expected to induce a higher rate of degradation.

A significant reduction in downforce on the new aerokit means less lateral load is put through the tyres, but cars are more likely to skate across the track surface, causing a greater rate of wear.

Cara Adams, Firestone's chief engineer and manager of race tyre development, told Autosport: "We're testing four different street course compounds to try a few different things.

"One is to try and limit the amount of drop-off on the primaries for tracks like Detroit and Toronto, tracks where there are different surfaces. You have a lot of concrete in addition to the asphalt.

"We're looking to see if we can find a primary tyre that is more endurable over an entire stint.

"Some may be in the range of what a primary would be and some may be a little softer, could be used as either a primary or an alternate, depending on what we see from the test results."

While Firestone intends to introduce a new rain tyre at the Detroit double header in June, the new street course tyre would not come in until mid-July at the earliest.

"The earliest we might use them is Toronto," said Adams, "but it depends on what feedback we get from the first race of the year regarding current tyres. The introduction may wait until 2019.

"We'd like to see how the current tyres run in the first and second street course races of the season - St Petersburg and Long Beach.

"Based on our own data and feedback from those two events, along with what we learn at Sebring, we can then decide what we introduce and when."

There are only four street course venues on the 17-race IndyCar calendar, with Toronto the last of those.

Adams added Firestone would ensure neither Rahal or Foyt gained an advantage from its drivers being the first to experience the new rubber.

"It's written into the rulebook that we can only test with a single team twice," said Adams.

"If it's something like an alternate compound, we won't tell the teams that tested it which specific compound we've gone for.

"So they'll have tried several and won't know any sooner than the other teams which one of them we chose to put into production."

Carlin will share the Sebring track with Firestone next Monday, with other cars joining over the following two days.