Lewis Hamilton blamed a decision to switch rear wings for his eighth place in Belgian Grand Prix qualifying.
Hamilton used a different wing that made his car slower on the straight than McLaren team-mate Jenson Button, who took pole position.
"Jenson has the new rear wing on, I have the old," tweeted Hamilton. "We voted to change, didn't work out. I lose 0.4 seconds just on the straight."
The tweet was later removed from Hamilton's profile.
It was one of a succession of tweets about his disappointment following qualifying and his determination to make amends in the race. Some of the tweets, which contained swear words or colloquial language, have been removed.
Hamilton arrived at Spa on the back of his second win of the season at the Hungarian Grand Prix at the end of July.
However, he struggled to match his team-mate's pace in final practice and, following a session debrief with his engineers tweeted: "Car is not fast enough at the moment but have made some big changes."
One of those changes would see Hamilton move to a high-downforce set-up, while team-mate Button was more comfortable with the new low downforce version.
The differences would mean Button would have more speed on the long straights in sectors one and three, and Hamilton more pace in the tighter middle sector but in theory their total lap times should have been similar.
Hamilton told BBC Sport: "It has not been a great qualifying session for me. We opted to use an old wing. After P3, the new one wasn't feeling so great.
"We went to the old wing and it was an awful lot slower. I'll just have to do the best I can. I will try and do as best I can to back Jenson up tomorrow."
Team boss Martin Whitmarsh said he thought the decision to put Hamilton on a higher downforce set-up was a "mistake".
But technical director Paddy Lowe said: "We had a special rear wing for Spa and Jenson stayed with that configuration.
Lewis was quite a bit slower than Jenson this morning and we elected to go for the high downforce set-up.
"It's a perfectly valid choice around here. It's not as though it's some sort of outlandish gamble. It's a choice we had seriously considered coming here.
"It's a long race. One of his principal competitors here, Kimi [Raikkonen], has gone the same way, and we'll see where it gets us.
"We will be looking at the differences and why we couldn't get the same performance, which ought to have been there on paper. The lap time is not explained by the differences in set-up.
"Perhaps we over-reacted, but it's a long race. Tomorrow is race day when you score the points and both will want to win and they're both capable of winning.
"Last year, Jenson came from 13th to third."