I am however curious.... as to why snowmobiles use this type of drive system?
I'm curious as to why sleds dont have "user shift-able" transmissions. Wouldn't it be even more reliable? Bang through gears like you can on a dirtbike, or a streetbike, and have a much wider range of track speed that way?
Sleds don't roll very well. There is a lot of resistance due to the track and the snow. Wheels roll, tracks don't. In order to shift a transmission with gears, the load must be removed momentarily in order to shift gears. It would be difficult to maintain momentum given the reasons I already mentioned. Yes, there are gear transmissions that can shift in milliseconds but they cost a fortune and are relatively heavy.
Motorcycles have 6 gears, and you can use each gear ALL the way through the motor's RPM to redline. It's not one consistant power, it's variable depending on which gear you're in.
What would be wrong with one consistant power...as long as its maximum power? Actually, the perfect transmission would allow you to hit maximum RPM (and thus max power) and stay there all the way through the transmissions' shift ratios. An even better transmission would automatically change gear as the load changed, with the engine staying at peak power. Go one step further and have an infinite number of gears available so you are always delivery this maximum power in the most efficient way. This, my friend, is what the continuously variable transmission...or CVT does.
On the other hand, a gear transmission forces you to let off the power, shift, then let the RPM build again to peak power, at which time you repeat this in order to get to a taller gear. Unfortunately, each time you shift, you momentarily lose power. Years ago the Williams F1 team put a CVT in one of there F1 cars and immediately proceeded to break the track record. The driver was able to keep the car at max power between each corner, never having to lift in order to change gears. The CVT was immediately band by the FIA. Even in today's F1 cars, although the gear changes take place within milliseconds and the driver doesn't even have to take his foot off the gas, they are still forced to spend time off of their peak power curve. These transmissions are built extremely light, at considerable cost, but I hazard to guess that if they allowed a team to use a CVT, the CVT car would win.
http://www.youtube.com/watch?v=x3UpBKXMRto