Why do some bicycles have so many gears?

Question: A lot of bikes have 21 gears - does anybody use all of them? How many gears do professional racing cyclists have? How many gears do professional mountain bikers have? You only need five gears, maybe 10 maximum, to get up hills, Sid. I remember people coping quite well with the limited number of ratios provided by the Sturmey Archer 3 speed as well. MR, you are an arrogant muppet. Shut up you fool!

Answer: Actually, you can't use all the gears in a bike. That means you shouldn't cross chain (use the leftmost gear at the front ant the rightmost gear on the rear, or viceversa). So a 27 spd mountain bike will likely have only 13 or 14 usable gear combinations. Having this range will make the bike adapt better for the type of riding you're doing at any single time. If you're on a long climb you could use a low gear, but if you want to clear a short steep climb, probably a mid-range gear would let you stand up and hammer. Or if you're on paved roads you would want a larger gear. About mountain bikes, most bikes comes with the crankset with 3 gears and on the rear with 7, 8 or 9 speeds. Mostly, the largest gear at the front is seldomly used. Some bikes go with only 2 or a single gear up front, depending again, of the type of bike (freeride bikes usually replace the largest front gear for a bashguard, and downhill bikes usually have only a single gear upfront with a chain guide). Most mid to high level bikes come with 9 speeds at the rear. Road bikes are sort of different, or the gear ratio are. Usually, I think they come with two gears at the front and 9 or 10 spd at the rear.

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