I have been following the IOM races since 1966. Back when they had 50cc, 125cc, 250cc, 350cc, and 500cc classes. They were all very exotic machines back then. Some of the little 50cc bikes were twins with 14 speed gearboxes. Honda had a 125cc DOHC four valve five cylinder that would turn over 20,000 rpm. All this through (if memory serves) a ten speed box. Man- the music that little bike made when running through the gears!
The riders all wore little "pudding bowl" helmets and thin leathers back then too. Skinny little tires on alloy wheels that wore drum brakes hooked to suspension that had maybe three inches of travel. Then men that rode those wicked little bikes has some serious cojones back in those days.
I used to have a 33 1/3 LP of the IOM races that I would play over and over listening to all the exciting machinery of the day. I wish that I still had it or better yet could find it on CD. You just aint lived unless you have heard the sounds of Mike Hailwood slamming through the gears on a six cylinder Honda 250!