This is a very complex question, and it depends on many variables, the most important one being tyre wear.
As a F1 tyre is used, it evolves, getting better as it heats up then worse as it wears out. Cars on new tyres are faster than cars on old tyres, in general, so the trick is to work out the best time to get new tyres.
The teams often use computer simulations to work out the best time to pit.
Generally, coming in to pit too early means wearing out your tyres towards the end of the race, but pitting late means 1) Going to long on gone off tyres in the first half of the race and 2) Wasting good tyres when you can't attack because you're in fuel saving (the cars are often short fuelled).
In practice that means the top teams often pit about 1/3rd of the way into the race: they start on used soft tyres from qualifying, which don't lost as long as the hard tyres they switch onto. This also means that when they go into fuel saving late in the race their tyres are worn so they can't get that much speed out anyway.
Also, if you are being held up behind a slower car, you might consider pitting then. That way you end up able to lap at your normal speed, and then get ahead of them when they pit.
so that they know how much weight they have lost
Formula One race cars
A Formula One race is called a grand prix.
Only one driver can take pole for a particular Formula One race
The iggest race in Australia is the Formula one race
1983
The winner of the 2011 Formula One race in India was Sebastian Vettel.
The second formula one race ever was held in Monaco on May 21st 1950.
Yes
Yes, it is one of the stepping stones up to Formula 1
twenty (20)
No he does not or he would not be able to race in Formula one.