Valentino Rossi looks set to continue with a new Yamaha chassis for the remainder of the British MotoGP weekend, but has doubts over the latest swingarm.
The Italian had requested to try the parts again as soon as possible after a positive impression at the Brno post-race test.
Yamaha duly provided them for Friday practice at Silverstone, which Rossi finished in sixth place, 0.841s from Andrea Iannone.
"At the end, I like the new chassis that I tried in Brno. I have more-or-less the same feeling, so I think we will continue," Rossi said. "I have more doubt about the swingarm. For me I don't feel a great improvement. So I don't know if we will continue to use it tomorrow."
As in the Czech Republic, the new chassis helped Rossi on braking and corner entry, plus "the feeling of the bike on the bumps, with the brake. Also for turning is okay. Is nothing very big, just a small modify, but it improves the front end."
Trying the new parts meant Rossi had a busier than usual Friday, and was therefore grateful that the MotoGP class got two dry - if cool - sessions.
"Difficult day I think for everybody because the conditions are quite bad, because it's cold and the track from the beginning was quite dirty. So not a lot of grip," Rossi said.
"This made everything more difficult, but at the end with the MotoGP we are lucky because we are able to make both practice sessions with full dry conditions that for me personally was important because I have the new stuff to try.
"Also, here especially the rear is quite difficult with both tyres. The soft that I try at the end you can make a better lap time, but I don't know if it's enough for all the race. Also the front the situation is quite similar."
Rossi - who starts round twelve of the championship 53-points behind title leader Marc Marquez - was particular impressed by the form of Friday leaders Iannone (Ducati) and Maverick Vinales (Suzuki).
"I'm similar to Lorenzo and Marquez, but have especially Vinales and Iannone stronger than us. Because with the hard tyre they are able to make very very fast lap times. A lot faster than me. Also with the soft they have a quite big advantage," he said.
"I think that they are in a great moment of shape because also if you compare with [their team-mates] Espargaro and Dovizioso the difference is quite big. That means they are riding very well. And looks like me and Jorge are in a little bit more trouble with the Yamaha.
"We are not so far but we have some places on the track where usually Lorenzo is always very strong and also he suffer. So we need to improve the balance and improve the speed. We hope that we can recover the gap to the top guys."
Lorenzo was fourth fastest and Marquez one place ahead of Rossi, in fifth.
By Peter McLaren