Improving Your Shifting
Most mountain bikes have three chain rings in the front and six to nine gears on the rear cog set.
The number of speeds on a bike is determined by multiplying the number of front rings with the number of gears in the rear. For example: 3 X 8 = 24 speeds – BUT, there aren’t 24 “usable” speeds. I’ll explain further….
The lowest, or easiest, gear in the front is the chain ring with the smallest diameter and the lowest gear in the rear is the gear with the largest diameter. So, for the steepest of hills, you would be in the smallest ring in the front AND the largest gear in the rear. The highest gear (used when you’re traveling the fastest) would be the opposite: the largest ring in the front and the smallest in the rear.
Problems occur when you start to “cross-chain”, which means having your chain cross from the smallest chain ring in the front to the smallest gear in the rear – or vice versa – the largest chain ring in the front to the largest gear in the rear. In the first case the chain will be too loose and will slap around when you hit bumps and can easily come off – jamming up your drive train and possibly causing damage. In the second case, the chain will be too tight AND will be traveling across from front to rear at an angle. This sideways strain being put on the chain which will wear it out prematurely. Try these configurations and you’ll see what I mean.
So, remember, never “small to small or big to big”.
Many cyclists don’t realize that those same gear ratios can be obtained using other combinations. You can go to the middle chain ring in the front and use the full range of gears in the rear because now you’re not stressing your chain sideways as much – AND you’ll be able to find the same gear ratio.