how would those 2 drivers know the limit of the car and tires which change with every lap if they didn’t cross the line a few times?
Ah… now we’re talking! The answer is “feel.” All drivers drive, according to “feel.” The difference is HOW the drivers get their feel.
At the very basic level, a driver is like a calculator – but it all happens subconsciously and instinctively. They receive a set of sensations, which their brain instinctively processes, and this tells them whether or not they’re on the limit.
That’s a very basic explanation.
The difference which I said above, really, lies somewhat in the driver’s habits. Some drivers build up to it – others build down to it. Take the example of Button and Hamilton. Button will take time to get a rhythm, then slowly keep on increasing, until his spine senses that the car is moving around slightly too much, and backs off. A Lewis would, in his own words, “you try to go flat out first. Then if you go off – you back off. If you still go off – you back off a bit more. Eventually you reach the limit.” I think it’s quite clear which is which.
Now you’re absolutely right that because track conditions change – due to temperatures, rubbering in, cars change – due to fuel loads, temperatures, tyre state (I’m going to include the tyre as part of the car in this post – because for that moment in time, the tyres are basically a part on the car). Weather complicates things further if moisture and precipitation is involved. A car that takes Turn X on Circuit Y at 160kph, might only be able to take it at 155kph the next lap. Absolutely true.
But while the limit changes – the SENSATION of the limit does not. Try doing some track time, and you’ll know what I mean. (Disclaimer – as I’ve said before, I’ve never had kart time, and karts are a whole different beast in terms of vehicle dynamics, so I bow down to any kart knowledge anyone else has)
The car would feel slower when taking the corner the second time at 155kph, but the sensations in terms of the car’s responsiveness, rotation, and slip – would be, relatively speaking, the same to what the driver felt at 160kph the first time.
Judgment also plays a big part. There are some aspects of driving a lap where you generally won’t feel that it’s too late until it IS too late. Braking is such an example. What you do is, basically, go instinctively based on experience – of past laps, and how the car behaved in the corners prior to that. That’s why you see a lot of a driver outbraking themselves, or braking cautiously, early on – and only really being confident when they’re finally back in a good rhythm.
Lewis in Abu Dhabi was a good example. His restart lap he was obviously a bit cautious, and the lap after that, he decided that he should push X amount more into the braking zone at 8 – and his judgment on that particular occasion was wrong.
As a driver develops – even a beginner – what they’ll develop is a map of reactions – in other words, when I feel X happening, I do Y. This becomes very instinctive.
Obviously in a case where a driver is trying that little bit more lap after lap – they’re human, and so they’re prone to mistakes too.
But note that not all drivers are constantly straddling 100%, especially in a race situation. A driver such as Button often drives at a constant 99.9% (arbitrary number) – he’s a bit like Jackie Stewart in that sense, driving at 9 tenths rather than 10 tenths – but he doesn’t push his luck with 100%, because he knows he’s human and doesn’t want to risk losing time by overstepping the limit. But because he gets so comfortable with a rhythm of pushing 9 tenths, he can be very consistent. Take a look at data from India 2011 and you’ll see what I mean. It was just a masterclass in consistency as he strung something like 12 laps all within 5 hundredths of one another. Or take a look at Melbourne 2010 – Button was just taking his time and doing his thing, with a beautifully balanced rhythm – and his 52 lap stint on the option tyre was (almost, but not quite) an exercise in 156 green sectors on the timing board.