Williams driver Pastor Maldonado was fastest in a wet second practice session at the German Grand Prix.
The Venezuelan, winner of the Spanish GP in May, was 0.088 seconds quicker than Mercedes driver Nico Rosberg, with Red Bull's Sebastian Vettel third.
In the drier, but still rain-hit, first session, Jenson Button headed McLaren team-mate Lewis Hamilton by 0.498secs.
Michael Schumacher crashed his Mercedes coming into the Stadium section in the closing minutes of the second session.
The German legend lost the rear of the car coming through the fast fourth-gear right-hander called the Mobil 1 Kurve and spun across the track into the wall.
"Basically I was not fully concentrated. I was on the radio and I was doing some other changes to the car, and touched the white line. That's it," said seven-time champion Schumacher.
"Cosmetically it looks [like] almost all four corners touched on the barriers, so that's not the nicest way, but the impact wasn't too big."
But he said he was confident of a good weekend.
"It's OK. Any time we've been out, we've been top end."
BBC F1 technical analyst Gary Anderson said: "Last two minutes of the session and probably £200,000 worth of damage, so that will be an expensive night for Mercedes."
In the course of two sessions in tricky conditions, only two other drivers terminally lost their cars.
Toro Rosso's Daniel Ricciardo, in the second session, and Williams reserve driver Valtteri Bottas in the first beached their cars in the gravel after losing control during braking for the Sachs Kurve, the hairpin in the Stadium section.
Hamilton was two seconds off the pace of Button when the track was at its quickest and Anderson said McLaren would have to look at why that was.
Hamilton was also slower than Ferrari's Fernando Alonso, the world championship leader, when running in the wetter conditions towards the end of the session.
The teams were trying out upgrades aimed at improving performance, with greatest attention focused on McLaren and Lotus.
McLaren have introduced redesigned sidepods, aimed at improving airflow over the car and closing the gap in performance that has opened up between them and championship pace-setters Red Bull and Ferrari.
Lotus were trying out their own version of the 'double DRS' straight-line speed boosting device pioneered by Mercedes at the start of the season.
Unlike the Mercedes system, the Lotus device does not work by ducting air from the rear wing to stall the front wing.
Instead, there are air intakes around the roll-over bar behind the driver's head and a new central pylon in the middle of the rear wing.
It appears air is taken in through the first, through the car and up the second, stalling the rear wing further and giving an extra boost in straight-line speed.
It is not yet known whether the device is linked to the DRS moveable rear wing system or - as seems more likely - operates when the car is going beyond a certain speed.
The system is being trialled this weekend and the team have not yet decided whether it will be raced.
If it is, it will only be on Kimi Raikkonen's car as it is too much work to fit it on team-mate Romain Grosjean's in time.
As far as McLaren were concerned, Button had said on Thursday that McLaren were optimistic they would be a step forward.
"Here we come with mechanical upgrades, aero upgrades, so hopefully they will work well. I have to believe they will, they're very straightforward, so we should put them on and go faster. It's a pretty good chunk.
"You'd have to say Ferrari and Red Bull are the two who have stepped forward compared to everyone else and I think that's just big updates.
"Ferrari have been consistently fast since Barcelona [in May], where they had a big update and their results have shown that.
"We haven't had a big enough update to be in the mix. Here should be that update and I hope it takes us back to the front."
McLaren sporting director Sam Michael said: "Today is all about testing them and so far it's looking pretty good. We have new sidepods and a few other things under the skin.
"Basically the undercut hugs closer to the car so you're not pushing the air so far out before it gets to the Coke-bottle area. It's just a much nicer solution."
Anderson said: "McLaren are pretty confident in their updates - they have decided to just believe in the wind tunnel."
Mercedes driver Nico Rosberg will drop five places on the grid as a result of a penalty for changing his gearbox. Romain Grosjean of Lotus has the same penalty after changing his after the British Grand Prix.