I can only go by the feel/feedback I get when I'm riding. I get this through the bars, seat and foot pegs. My brain attempts to process what is happening at both ends as well as control my bodily functions that are controlling the bike and while working out what the hell is happening all around me and where I'm going next - probably why I don't know the answer
I'll push it as hard as I feel confident that the tyres will still grip, but that is partly suspension as well as the tyre working. Also, I rarely push it over the limit as I think I am a reasonable judge on grip and I think my corner speed is OK.
I'd also have to look at the tyre after some laps, to see if I'm chewing it up or what's happening.
Whats the real answer?
