In an engine the piston rings have to fit very snugly inside the cylinders. They seal to the cylinder wall, a metal-to-metal seal. It used to be hard to make piston rings that accurately, so they would have to wear in over the first 1000 km or so. (The piston rings are softer than the cylinder walls, so they wear instead of the cylinders.) During this time you would drive under a certain speed or else you could get 'glazing'--the cylinder walls would harden from excess heat and the piston rings would never seal. Also after this break-in period you'd change your oil and the oil would be full of black powder which was what wore off the piston rings as they wore in. During WWII, new aircraft engines were hooked up to enormous electric motors that would just spin them for 24 hrs before they were put on an airplane.

These days, piston rings can be made a lot more accurately so the break-in period is not as important. But it's still not a bad idea. The last new car I bought (well, the only new car I ever bought) was in 1994, and they told me a break-in period was not necessary. But I did it anyway, and when I changed the oil at 500 mi. it was still full of iron filings from the piston rings.

Anyway, they tell you never to exceed a certain speed. But you can, just so long as you don't drive any particular speed for a long time. Taking the bike on the highway and riding 100 km/h for an hour would be bad.

30 miles and hour for 1200 miles? Seems a little silly. Most recommended break-in periods are 500 miles/800km.

Basically they want you to take it easy for a while so you don't break the bike. New parts need to wear together, hard riding can cause damage to parts that are still wearing in, mostly internal engine gears and other moving parts.

I think you're talking about wearing in a new bike, its engine and parts. Basicly, alot of people state that you should not hold it at high RPM's or full throttle etc for long periods of time. You want the new parts to wear in gently, without being to harsh on them. So, it's best to ride a new bike smoothly for a while, with the odd occasions of quick blasts, but not long ones. You dont want to ride it aggressively everywhere.

you'll hear alot of opinions .. what happens imo is this: when a vehicle is new EVERYTHING is tighter and moving parts are not 'polished in' ... what this can do is create increased drag and heat which can expand parts and cause them to wear in a way that is not ideal .. an easy slow break-in will insure everything initially wears in and smooths out without that unnecessary wear ... anyone that says 'modern' mechanical things dont need to broke in is swept away by the ignorance on the internet .. you'll even see some suggest 'hard' break-ins, which is the most sure way to turn your nice new bike into a pos you can do ..

its the break in period.