Advanced Driver Warmup
When I was an intermediate driver, and it was my first weekend at Watkins Glen, I got a ride with an instructor. What I remember from that session was how late the instructor started braking for turn 6 - on the out lap. I thought to myself "Hmm, this is pretty aggressive. Are we going to stay on the track?" As it turned out, the car experienced a suspension failure in that braking zone and we ended the session in the tire wall in that turn. The experience though remained.
Fast forward several years. I am now an instructor and people ask me for rides.
At VIR event this November a friend asked me for a ride. I have generally been wondering why i take as long to warm up as I do, and in that session decided to "go for it". We have been stationed in the South paddock, and I took the roller coaster, which is the first turn after pit out, at a good clip. After the session, my friend commented how he did not think we were going to stay on the track. In actuality there was still a substantial margin between what the car did and what it was capable of, even on the out lap.
So, what do I know about warmup now?
The tires can only cool down so much in the 30 minutes to an hour that instructors often have between sessions, especially if they take passengers. There is a difference between warming up a car that just came to the track on a trailer at 8 am and warming up a car that was doing hot laps half an hour ago. While the tires are certainly not at 10/10 pace temperature, they can easily be at 8/10 pace temperature in the first corner.
I am confident that the car can run the first lap of an afternoon session at 8/10, with experience to back up that confidence. This experience obviously comes from seat time, but not just any seat time - time spent pushing ever so slightly harder on the out laps.
If you mention "pushing harder on the out lap" to any track staff, you at best will get a nasty look. Doing the pushing just barely rather than all out is something that you learn by experience and, again, seat time. Before you start with this you should have confidence in your abilities to restrain yourself and push carefully.
Effective Cold Warmup
Why do some people spend an entire session warming up? It is because they are not doing the warmup effectively.
Driving in straight lines at easy throttle, at low rpms, and barely moving through corners is not getting heat in the tires when the ambient temperature is 40 degrees F. You need to put meaningful lateral and longitudinal loads on the tires for them to heat up. Effective warmup is like driving in the rain - you are constantly feeling how much grip the car has, and if it has more grip than what you are using, you go faster.
You don't want to flat spot the front tires during warmup, so take it easy in the braking zones. However, especially if you are on old tires that take longer to warm up, spinning the rear tires coming out of corners is not the end of the world, just like in the rain it is not. Be careful not to be so aggressive that you depart the track.
Effective warmup is a skill, as is driving the first lap fast. All racers need it, and time trialers in high horsepower cars typically need it as well.