The focus after drivers walked the track earlier this week were some of the aggressive kerbs around Singapore's new formula one street circuit.

But with three hours of practice under their belts, Nico Rosberg's headache and Adrian Sutil's bruised legs were testament to the new big issue: bumps.

"It's much bumpier than what we have experienced before," Renault engineering boss Pat Symonds said on Friday. "It reminds me of the North American circuits in the 1980s."

F1 veteran David Coulthard expects a lively weekend.

"It's like the cobbled streets of Paris and very unforgiving. I think there will be a lot of incidents," the Red Bull driver said.

Lighting was also a post-action talking point, after organisers' earlier boasts that the circuit would be four times brighter than a typical stadium.

"When I walked the track I was impressed, but behind the wheel at 300 kmh some parts of the track are a bit dark," said former world champion Fernando Alonso.

Other drivers backed the Spaniard, but some reported no problems whatsoever -- including F1's only bespectacled racer, Sebastien Bourdais.

"I even ran with a lightly smoked visor. There are hardly any shadows and you can see very well," said the Toro Rosso driver.

Bourdais is less impressed, however, with the pit lane entry, which on Friday he described as "incredibly dangerous".

"It could be quite difficult if a driver decides to pull into the pits at the last minute," McLaren driver Heikki Kovalainen agrees.

Ferrari's Felipe Massa believes the pit exit could also be "a bit critical" on Sunday afternoon.

"They are both pretty difficult and we will have to be very careful," his teammate Kimi Raikkonen concurred.

Source: GMM