Despite having had a lot of opportunity to test on a wet track as rain continued to dog the F1 circus in Germany, McLaren duo Jenson Button and Lewis Hamilton remain cautious about the potential of McLaren's latest upgrades should qualifying and the race be afflicted in the same way as practice at Hockenheim.

Although the pair put the heavily revised MP4-27 at the head of the timesheets in morning practice, they did so in relatively dry spells at either end of the 90-minute session. When the heavens opened and prevented a return to those conditions after lunch, Button managed only eighth place, with Hamilton way back in 19th, although Button did manage to momentarily sit at the top of the pile as the order revolved during a brief drying spell.

"We only had a couple of laps in the dry and we didn't get to back-to-back them so that we could start off with the car from the last race and then put the new stuff on," Hamilton told Sky Sports News, "We won't know [where we stand] until tomorrow and, if it's wet, then we might not know until the race. It's definitely a step forward - the car felt reasonably good all day, so a really good job from the guys - but how much [of a step] it is, I can't really tell you."

After a disappointing performance in its home race two weekends ago, McLaren has brought several developments to its car in Germany, with both Hamilton and Button running with a host of cosmetic tweaks - including a redesigned engine cover, sidepods, brake ducts, diffuser and rear wing - as well, according to team principal Martin Whitmarsh, an equally substantial list of changes 'under the skin'.

Button was immediately on the pace in Friday's morning session, vaulting to the head of the times in the opening 20 minutes, and then watching as his rivals attempted to play catch-up between the showers that swept across the Rhine region. On the final quarter of an hour proved good enough for improvements, with Hamilton coming closest to toppling his fellow Briton, before eventually ending the session half a second shy in the company of Fernando Alonso and Michael Schumacher. The afternoon, however, told a different story.

"Trying to get these wet tyres working is one of our big issues," Button told the BBC, "There's a lot of work needed to prove we can be quick in the wet because I think it could be wet tomorrow."