Bicycle Mechanics - modifying my old mountain bike

My old mtb bike needs a total overhaul and I got to thinking about some modifications to it that would be more suited for the use it's been getting.

I thought about replacing the stock 7-speed rear hub with an internally geared hub. This, to accomodate the new and beginning riders (such as my girlfriend) who've been using it who find proper shifting a real challenge. There's been times I wished I'd had a way to shift while stopped on that bike myself.

I haven't had a bike with internal gears since I was a child. What happens whe you need to change a flat? How difficult is it to detatch the wheel with such a gearing system? Easier?

Are these things a bad idea?

Hub gears are a great idea on utility bikes, not only for beginers.
You can change on the move or when stopped. These days, 5 speed is a good minimum, and 7spd is better.

You need to have rear dropouts that are horizontal, so that you can move the axle back and forward to adjust the chain tension.
If the dropouts are vertical, then you need to add a chain tensioning device which adds complication.

Changing the wheel out is not that difficult. The Sachs models are probably a bit easier than Shimano (and all round better hubs).

http://www.sheldonbrown.com/seven_speed.html

Changing to an internal hub is very easy - assuming you don't have to rebuild the wheel yourself.

I like internal hubs. They make a lot of sense; cleaner, easier mainenance, enclosed gearing.

However, I don't think they would hold up well to really punishing mountain trail use.

I've only used old Sturmey Archer Three Speeds, and changing a wheel on them is pretty idiot proof, and takes no longer than on a derailleur geared bike.

Richard

Rohloff internal hubs are specially made for off road use.

Sachs 7speed hubs have been used for expeditions across Asia, and hold up well to years of hard all-weather commuting.
They are not designed for pushing hard at very low gears, but for jut riding trails, they are quite strong enough.

If you replace your cogset with an internal hub, you will be stuck using only one chainring, unless you keep the rear derailleur as a tensioning device. Doing so will give you an incredibly wide 21-speed gearest.

Like John said, keep the rear derailleur as a tensioning device, and run two or three chainrings up front. If you choose to have a coaster brake, the removal is a little more difficult when flat fixing.

Anders K
Sweden