The other day, with 1.5 laps left in a cat 3 crit, the guy in front of me reached down into his bottle cage, grabbed his bottle, and threw it wildly onto the sidewalk, almost hitting a spectator.
This process caused him to open up a two or three bike length gap in front of him which he then had to pedal hard to close... almost certainly negating any gains he made by losing the weight of the bottle for the final sprint.
So I'm pretty confident that this particular bottle-throwing instance was a poor decision, but it motivated me to look into the
actual savings of the bottle-throw, which is really just an excuse to blog about PHYSICS!! And who doesn't love MATH?!
IMPORTANT NOTE: Throwing your bottle creates trash. Trash creates unhappy residents on race courses. Unhappy residents create problems for race promoters. If you're throwing your bottle onto someone's lawn -- you are the kind of racer that all promoters hate. Don't do it.
Let's set some ground rules:
1) A full bottle weighs one pound (0.45kg)
2) The aerodynamics of your bike are basically the same with or without the bottle.
3) The placebo effect of throwing the bottle doesn't make you go faster.
We're going to use energy equations to solve this. The equation for kinetic energy is 0.5*mass*velocity squared.
The equation for potential energy is mass*height*gravity (9.8m/s/s).
If the sprint is uphill, what benefit does throwing the bottle give me?
My body and my bike also have significant kinetic energy here, but they have the same energy whether there's a bottle attached or not, so it doesn't matter.
If the sprint is flat, what benefit does throwing the bottle give me?
(Oh and there's probably no way you can accelerate from 35mph to 40 in 12 seconds, because you're a scrub, I was just using some really optimistic numbers to illustrate that throwing you bottle is basically meaningless here, too)
What if I'm at the bottom the steep part of Middlebury Gap with a full bottle on my back in the Cat 3 race?
If I could lose five pounds of old-man-metabolism fat between now and GMSR 2017... now I'm down eight pounds... at the same power I'd go over Middlebury gap 33 seconds faster... oh god this is how cyclists get eating disorders, isn't it?
So, uh, don't throw your bottle, ever. But if you're gonna throw your bottle, throw it along with your spare tube and CO2 and GoPro and 5 pounds of fat, so you don't get shelled by the freaking Cat 3 field on Middlebury Gap.