McLaren team principal Martin Whitmarsh has aired his concerns regarding tyre degradation after today's practice sessions for the United States Grand Prix.

The 54-year-old admitted that his team have not got the best from their tyres in previous races this season and has targeted an improvement in Texas.

"Today the circuit seemed very shiny, I think it's exacerbated by reasonably conservative tyre choice here," said Whitmarsh. "So I think we're going to have to work hard - certainly we know we've got to work hard on low fuel.

"We found it a little bit easier on high fuel, which suggests we weren't working the tyres well enough on low fuel."

Whitmarsh spoke of the newly-opened Circuit of the Americas as it prepares to host its very first grand prix.

"Some of the corners have got some unusual challenge which makes it an interesting challenge," he added.

"It's slippery, there's some interesting cambers on the circuit and some interesting compromises you've got to find between the vast variety of corners that we have."

Championship leader Sebastian Vettel went fastest in both of today's practice session.