Originally Posted by Timbeau

Well... they can.

There's a large number of IGH hubs on the market, and they vary greatly in price, from a couple of hundred to a few thousand dollars.

They have advantages and disadvantages. Some say they put too much weight on the rear axle. Some think they may not handle high torque situations that one would find mountain biking. Some like them because there's no derailleur to break, or chain slap, that they're less likely to be affected by mud, etc. There's a lot of opinions on who's hub is best for this or that application.

I have read some positive things about this hub (Shimano Alfine 8 speed), and in particular, people's reports about their real world experience using it mountain biking. I'm not some Double Black Diamond rider, I don't do big hits, or anything like that. I ride fire roads, flowy singletrack, and love doing long downhill trails; this hub has no problems handling all of that.

That being said, ALL internal gear hubs are persnickety: they need to be set up correctly. Just so. Any number of little things can throw them off. I know some bike mechanics are less familiar with them, so be prepared to just learn how to do things yourself. That requires special tools, taking the time to learn how to do whatever it is you need to do. Removing/replacing the rear wheel takes a few extra steps. Can be a hassle (but certainly not impossible) to change a flat in the field.

But, when they're set up correctly, they're sweet as pie. I really like hub. It seems rugged, gives me a nice range, it feels faster than I was expecting. I'm very happy with it.

What do you have in mind for a klunker? You should totally build one. Everyone should build a klunker.