Alonso blames poor Spa result on tire strategy
Alonso, who topped Friday practice but qualified in 10th, said Ferrari did not have enough fresh sets of soft tires.
"In final qualifying I had one new set. We put it on at the end as we thought it was best but it rained," he said.
"Everybody had two new sets of soft tires but I didn't. The performance of the car wasn't for 10th."
The changeable weather during qualifying meant the teams had to switch between intermediate tires – meant for a damp track – and the harder and softer of the two types of dry-weather tires at the will of Spa's skies during the three parts of qualifying.
Red Bull's Mark Webber set his pole-winning time of one minute 45.778 seconds during a window of drier conditions but Ferrari failed to anticipate the final flurry of rain.
Alonso set his fastest time – 1.663 seconds slower than Webber – in that same window but said that lap was set using the same tires that he had used in the second part of qualifying as the team chose to gamble on the assumption that the track would stay dry enough for a final run on a fresh set.
"Everybody needed the same thing, one timed lap and then another timed lap," added Alonso.
"But they then had two new sets of soft tires because they didn't use them in Q2 so that was the only thing.
"I'm not surprised because when there is wet qualifying anything can happen; we nearly went out in Q1."