Originally Posted by
black_box
I'll take a stab at this and say "a little." The potential energy you gain from climbing the hill = mass * gravity * change in height. Going down the hill converts that potential energy to kinetic energy (0.5 * mass * speed^2) but the faster you use it up (i.e. higher speed) the more is lost to wind resistance (doubling your speed = 4 times as much wind resistance). Basically, going down the hill faster will be a less efficient use of the energy you stored when you pedaled up the hill.
Good explanation of the energy equation!
The simpler explanation is that you can't really go fast enough to make up for the loss of time that going slowly uphill costs.
Originally Posted by
WhyFi
Stupid but honest question - he's doing loops and ending at the same elevation that he started out at... shouldn't he be making up a little time on the down side, anyway?
Let's say there's a 10 mile run up a mountain. Let's say one travels up at 5 mph for 10 miles (2 hours) and coasts down at 40 mph (0.25 hours) (reasonable numbers for "normal" people on a "good" grade).
That ends up being 20 miles over 2.25 hours. The average speed would be 8.9 mph. If this course was flat, 15mph (in an aerodynamic position) would be fairly easy to do.
If you could increase your downhill speed to 80mph (just like umd), your average speed would be still low: 9.4 mph.
It's very hard to go fast enough (due to aerodynamics and the simple reluctance to go very fast on a bike) to make up the loss of speed going up hill for such a long time. (In my example, it took 8 times as long going up as going down.)
Hills do horrible things to your average speed!