Ben Spies battled to fourth place in the Dutch TT after fearing his tyre would 'explode' when he upped the tempo in the closing stages of the race.

The factory Yamaha rider was battling with the satellite YZR-M1 of Andrea Dovizioso seven laps from the end when 'chunks' of rubber broke away from his tyre.

The revitalised Texan had been running in third for much of the race behind Honda duo Dani Pedrosa and Casey Stoner before he was overtaken by Dovi.

Spies, now tenth in the championship table, said: "Today the bike was good, I struggled with some front grip in the beginning but was able to ride around it.

"I managed to stay past Dovi and ride at my own pace then about seven or eight laps from the end I was pushing to get away.

"A chunk came out of the tyre and then a second; I couldn't do anything about it.

"I was hoping Dovi would get past me as I was worried the tyre would explode and I didn't want to fall right in front of him," he added.

"We've made some mistakes early in the year but the last two weekends we've had a bike to be on the podium but issues have prevented it.

"The bike and the team are working so well and I've been really comfortable on it so it's disappointing."

Spies was not the only rider to suffer serious rear tyre issues at Assen - Ducati's Valentino Rossi being forced to pit for a new tyre.

Bridgesone Motorsport manager Hiroshi Yamada said the company will now investigate.

"I am sorry that some riders experienced tyre problems during the race," said Yamada. "We are now investigating the issue and will report back to teams with our findings at the next race."