I'm talking about tyres. And why I prefer a road bike with thin tyres.
In this vid, the bloke with the fat tyres gets away first, followed by the other roadie. The fat (tyred) bloke then pedals madly all the way down the hill.... and pedals madly up the other side.
But you may notice that after a few seconds, the guy on the road bike stops doing any work with the pedals and coasts. I was coasting long before he gave up pedalling. When we got to the hill, I was actually hauling on the brakes going up hill because the fat bike slowed down so dramatically.
It's all about lower rolling resistance and friction. Having thin tyres mean you can go faster, and that's what I like.