Short answer:
So that the cyclist
does not slide back down
Long answer:
The main forces a
cyclist must conquer are air resistance and gravity. Air resistance increases
exponentially with speed. In the switch from cycling on a flat road to hiking a
hill, the decreased speed reduces air resistance to the point where drafting
other riders offers small benefit. At this point, smaller cyclists, who have finer
power-to-weight ratios, will be able to break away from the peloton. Climbing skill
can be improved by minimizing weight, and also by pedalling at a constantly elevated
rhythm. Large cyclists can attain greater downhill speeds, but on mountainous
courses smaller cyclists still have a benefit.
