TT Video
 

The closing video of this year's TT
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and the fastest lap ever, this guy is nuts/smooth/fearless
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Do you think they memorize the course?

Absolutely.

Road racing is tricky enough even when you know where you're going!
It takes time, and a not inconsiderable effort, to get familiar with the, more than, 200 corners.

Rookies (well, sufficiently well funded ones) will hire a car, out of season, and do lap after lap, day after day, to try to ensure they have a decent grasp of which way the course goes.

I would think that in this day and age that sims are a big part of it.

I watched a race from the mid 50's last night on YT From IOM and they were haulin' butt, but there seemed to be a little margin left for error. A steel light post had one hay bail in front of it.