Lewis Hamilton says he was lucky to avoid a huge crash in Belgian Grand Prix practice

The McLaren driver suffered a major twitch approaching the high-speed Blanchimont left-hander during the morning session in conditions that did not seem suited to the intermediate Pirelli tyres he was using at the time.

"There was a huge river right the way across the track," the 2008 world champion said. "I must have been doing 150mph and had a huge tank-slapper.

"I'm lucky I was awake to correct it or it would have been all four wheels the front wing and the rear wing [off the car]. I'm glad I was on form."

With teams not allowed to change the set-up of their cars significantly between qualifying and the race, and changeable weather conditions expected for the rest of the weekend, Hamilton said that choosing the right downforce and gearing levels will be crucial to any chance of victory.

"Even before the weekend we knew it was going to be difficult because the DRS makes such a difference [to the way the car's downforce levels are set]," he added.

"You get past sixth gear and into seventh and in some cases, when DRS isn't engaged, you don't then get out of sixth. Also, with the fuel loads much heavier [at the start of the race] then it's going to make a massive difference.

"Setting up the car for qualifying is one thing, but making sure you don't lose too much time in race conditions without DRS is a big thing."

Hamilton was fifth quickest in the morning session before improving to fourth during the afternoon.