Mountain bike gear damage?

The speed at which you are pedaling isn't important, but the amount of pressure you are putting on the pedals while shifting can cause damage if you frequently try to change gears while pushing very hard on the pedals. If you are riding hard, components wear, in particular chains and cassette cogs. Even in ideal conditions these parts do require replacement eventually. It doesn't matter that your bike was expensive, regular maintenance includes occasional replacement of drivetrain components. Abusive riding style can accelerate wear