How does a rider define his optimum racing line at the track? Why do the MotoGP riders use a different line to the 250cc and 125cc riders? Is it just about weight and corner speed? Are there other factors involved? It there is only one perfect line, then why do you see so many lines being used?
Like a lot of observations, you end up with more questions the more you look into it. This is why I love watching racing and guys on trackdays and even riders who overtake on the road, then pitch their bikes into a roundabout ahead.
I'm always watching and asking - why? Why did it look like that? What did he do different to me and again, why? The line a rider chooses will dictate his throttle application, but equally, his throttle application will dictate his line.
The two go hand in hand. That's why you'll see late apexes trading places with double apexing riders sometimes.
If you don't own the soft science of road racing by Keith Code, the get it and read Chapter 10, Riding Plans. It's an ideal insight into the different lines used by different riders.
It is a fact, the slower you approach the corner, the later you can turn. By the same measure, the faster you are going, the earlier you will have to turn. But bear in mind that the rate at which you can turn also has a bearing on where you can turn, and at what speed.
If you had two riders approaching a corner at the same speed, the rider who could turn quicker could also turn later.