Mountain Biking - 24" rear Tire Why?

I have seen many many bikes up here with a 24" rear tire. I am trying to figure out why. I realize some bike are designed with that geometry in mind. But it sure wouldn't imrpove speed. Does it improve control it makes you sit back more allowing for greater control on tricks (is that true)...Just curious.

I have a 2000 Big Hit FSR, and I put a 24" rear wheel on it, even though it was designed for a 26". It rakes the front end out a bit, makes for crappy climbing (not that it climbed well before), and doesn't handle well on single track, but thats not what I use it for. Steep chutes, big drops and jumps are great, and it actually helps me go faster on the steep stuff because the wheelbase is longer, and the BB a bit lower. There is a picture of me riding it here (http://www.bikeforums.net/showthread.php?s=&threadid=11589)

The theory is that the smaller the diameter, the stronger the wheel. Plus, with the current trend to go to super fat tires(up to 3.5"), you need the extra room to fit such a fat tire into a standard frame.

Proponents of 24" wheels, claim quicker acceleration, and I buy that. Yet, I don't understand the longer wheelbase claim. Isn't a wheelbase measured from center to center? The frame must change in order to effectively change the wheelbase. Or am I way off here?

L8R

But with a 24" wheel wouldn't your overall speed be slower? And yes I can see the strength aspect my frames geometry would be screwed if I went with a 24" rear but I undertsand it. Possibly better balance.

As for wheel base. It is measured centre to centre but there is a wheel base measurement that is end to end. And a 24" wheel in theory would shorten your bike by 1". More useful for controlling? Just something I have been pondering for a while and considering every second rider out here seems to be doing it.

overall speed would be decreased because you'd pedal out faster, but initial acceleration would increase because of the smaller rotating mass in the rear.

First off – When going to a smaller rear wheel your overall gearing will be lower, but that doesn’t make for a slower bike, how often do you spin out the top gear on a downhill bike. I removed my big ring from my freeride bike, because I rarely needed that gear (gravity takes over), so my biggest ring is a 32. This allows me to run a much tighter chain, and what I loose in top gearing I gain in clearance and better shifting. I broke 45 mph in the dirt with a 32X11, of course I wasn’t pedaling.

Second, using a smaller rear wheel will increase your wheelbase. As the wheel gets smaller the rake on the fork goes further out, increasing the distance of the contact points of the tire. The shortest distance between two points is a straight line, right? Imagine a bike with 26” wheels; now imagine that same bike with a smaller wheel inside the rear 26” wheel. Now imagine two lines, both starting at bottom center of the front wheel, one goes to the bottom center of the 26” rear, and the other goes to the bottom center of the smaller wheel. The line going to the smaller wheel will be longer – it may not be much, but half of an inch is a long way in wheelbase.