Mountain Biking - Bike question? How come..

If I am goin like 15+ mph, the wheels are goin pretty fast. I'm jus curious, but how does the bike wheel spin so fast in the center where it joins the fork area without makin so much heat or something that it would mess something up?

That's why they invented ball bearings ;) The contact area of the balls are so small that the friction is almost negligible. Since there is very little friction, the bearings don't heat up too much.

The centre structure of the wheel, that the spokes attach to, is called the hub. It is a hollow metal tube, flared open like horn at each end. The axle is the straight rod that goes through the hub and is bolted to the fork. Hidden between the axle and the inside of the hub, at each end, are about ten small metal balls that are coated in grease and roll between the hub and axle. They 'bear' the weight of the bike,so this kind of setup is called a "ball bearing" and it ensures smooth, low friction wheel rotation.

Damn, you guys are good....

I always thought the mud just kept everything insulated.

Also think bout how fast the centre is actually moving. The speed of the two rubbing metals (which there are ball bearing between to make the friction even less) is moving much much slower than the outside of the wheel.

Also think bout how fast the centre is actually moving. The speed of the two rubbing metals (which there are ball bearing between to make the friction even less) is moving much much slower than the outside of the wheel.

This really is the key to your question. The outside of the rim is moving pretty quickly. At 26 inches in diameter and the circumferance is equal to D x Pi. 26 x 3.14 = about 82 inches per revolution.

The hub axle is about 1/2" so you are looking at 1.57" per revolution. The hub is rotating very slowly in relationship to the rim.

Damn, you guys are good....

I always thought the mud just kept everything insulated.

On some of my bikes, it has :p