I had read that in F1 unless they crash or have an equipment failure they use one chassis (ie body) until it breaks, problems are detected with it during testing or it crashes while changing the engine every 2 races and the gearbox every 4 races. They can also replace all of the others parts on that chassis as they want (ie suspension, wheels, etc)
I thought there was a rule in F1 that a driver must race the same chassis as they qualified in or else they have to start from the pit road (basically last place)
They do not have different chassis for different races the way that nascar does because they want the chassis to be as identical as possible so that if they crash/break one chassis they use the same settings on a replacement chassis.
Plus, I thought I read in an old article about the jaguar team (now defunct) that a team usually only builds/buys 5 identical chassis (ie body/frame only) for the entire season and only assembles 3 complete cars at one time. They bring 3 assembled cars and the parts for a fourth car to each race.
In fact, I thought there was a time many years when the ferrari team had a 3 rd driver testing in their 3rd assembled car crash during testing the friday before a race, then Michael Schumacher (main driver) crashed his car during qualifying so Schumacher then raced his co-driver's car (rubens barrichello) and rubens had to race the fourth car that was hastily assembled overnight before the race.
I have also heard that the really underfunded teams like Jordan or minardi in the past or super aguri in the present may only have a total of 3 assembled cars so if one driver crashes he gets the 3 rd car and if the other driver crashed he is out of luck.