Not that I want to go back and forth, but...I'm gunna go back and forth. Generally speaking, street tires are only good for 15 minutes with an experienced driver. A novice who's overcookin' street tires on a real road course (i.e. not autocross) is more than likely driving beyond his or her limits; an instructor would know this and tell the student to keep the pace down. Even if a novice was sufficiently talented to cook up a set of street tires during a 30-minute session, he or she would have an instructor in the car who would feel the tires starting to go and instruct the student accordingly.
As an aside, I've been doing this for three years and I still sometimes use street tires when I feel I'm getting complacent with R-Comps (i.e. when I feel that the R-Comps are saving me from my mistakes). So I go back to basics; and I don't over-cook my street tires; if I did, I'd slow down or come in.
Being on track is not just about going fast and having endurance; it's also about learning about your personal limits and those of the car and then acting accordingly. In other words, being on track is about learning personal restraint and responsibility; "growing," if you will.
I still maintain that 30 minute sessions are better. If a student can't handle a 30 minute stint the instructor will either instruct the student to slow or go in. It may be frustrating, but limiting yourself is one of this hobby's many challenges. Arguably, anyone who doesn't realize their limits or worse (e.g. realizes them and pushes forward with disregard) shouldn't be on track.
Last edited by Bayerische E46; 10-16-2012 at 02:53 PM.