George Russell sets the early pace in Miami
George Russell topped the timesheets on Friday as Formula 1 made its Miami debut.
Russell was second fastest in the opening session behind Ferrari's Charles Leclerc, but went one better in FP2 to set the fastest time of the day.
"We always knew that the warm conditions here in Miami would suit our car better - we've suffered with getting temperature in the tyres at previous races so that's a big factor here," said Russell.
"The car is running well but it's only Friday, we're not getting carried away."
Both Mercedes drivers experimented with set-ups on Friday as the team brought new front and rear wings to Miami.
"It's probably been the most productive Friday we've had this season in terms of learning," said Russell.
"We know that the porpoising will always be there but maybe it's working at a lower range compared to where we were previously."
Teammate Lewis Hamilton was eighth in FP1 before climbing to fourth in FP2, but the seven-time world champion echoed his teammate's call not to read too much into the Friday pace.
"Today is just practice and everyone is doing something different, not showing their true pace, so we won't get carried away," said Hamilton.
"The car feels similar to me but we seem to be quicker and we've obviously improved in places."
"We still have the bouncing so we haven't cured it but bit by bit, we're improving the car."
Times improved significantly through the day, with Leclerc second-fastest in FP2, and Red Bull's Sergio Perez in third.
Max Verstappen was on the back foot after having to make a gearbox change between the two practice sessions, but it Ferrari's Carlos Sainz whose streak of bad luck continued when he ploughed into the wall during FP2.
The field will return for a final practice session at 3.00am Sunday (AEST) before qualifying at 6.00am.