McLaren says its drivers have been surprised by the 'shocking' lack of grip during early running at the new Austin Formula 1 track.
Early practice was marred by a whole host of drivers locking up and running wide around the United States Grand Prix venue as the track surface proved very slippery.
McLaren technical director Paddy Lowe said it was too early to judge whether the lack of grip was down to a dirty track surface, or the actual asphalt characteristic.
"Going out initially, there is quite a shocking lack of grip," he said when asked about driver feedback from first practice.
"What remains to be seen is to what extent that is just dirt and to what extent it is the surface of the circuit.
"Obviously the circuit improves a lot during the session and there was a time when I wondered whether we would really get going, but everybody went for it."
He added: "Jenson [Button] was describing the experience as still very, very unusual. He says he is trying to almost rally the car around with so little grip, because you have to promote oversteer to get the car to turn. So, hopefully the track settles down."
Lowe said that the data provided to teams ahead of the weekend by Pirelli did not indicate that the surface would be particularly smooth.
"Pirelli do measurements that they supply to us and they would indicate that it is fairly similar to the roughness numbers to other new circuits," he said. "But it does seem to be at the moment behaving differently."
The tricky track surface has left Lowe in no doubt that the early times being delivered are not indicative of competitiveness for the Austin weekend.
"I think it is really difficult to read anything into what happened this morning, because the circuit was changing so much so quickly - and drivers were learning it at same time. The tyres went through quite an unrealistic cycle."