MONACO (REUTERS) - Monaco's unforgiving street circuit proved a bone-jarring, eye-popping ride for Mercedes drivers George Russell and Lewis Hamilton on Friday as they wrestled with bouncing cars and a bumpy surface.

The champions were struggling on a hot afternoon as Ferrari's local hero Charles Leclerc and Spanish team mate Carlos Sainz finished second practice one-two.

Seven times world champion Hamilton, winner of a record 103 races, said it was "probably the bumpiest track I have ever driven".

He said the car was also bouncing in a different way to previous races this season.

"I am fighting the car. To put a lap together is, wow! Holy crap! I don't remember experiencing it like that before," said the Briton, who was 10th and 12th respectively in the sessions.

"When you actually do try to put a lap together, the grip doesn't feel terrible, it's just eyeballs coming out of their sockets."

This year's cars are bigger and heavier than in the past, and the city streets subject to the rigours of regular traffic when not being raced on.

Russell, sixth in the second session, said the car was so stiff it was hard to drive it on the limit while the Ferrari drivers appeared able to smash over the kerbs without any problem.

"There are sections where both the (front) tyres are off the ground," added the Briton.

"At turn five you've got the front-right up in the air, and it's so stiff even the front-left is popping up off the ground as well.

"It's almost like doing a wheelie, with no front wheels on the ground."

Trackside engineering director Andrew Shovlin said the ride problems were preventing the drivers from properly attacking the lap, especially on low fuel.

"We made a bit of progress between the sessions, but we need to pick through the data and understand whether we can achieve more," he said.