Join Date: Feb 2007
Location: Tariffville, CT
Bikes: Tsunami Bikes
Mentioned: 12 Post(s)
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BMX'ers intentionally don't rock their bikes when accelerating from the gate. At low speeds (under 10-15 mph), apparently it's better to not rock since it's advantageous to transfer pedaling power into forward motion as quick as possible, even if you aren't as efficient or powerful.
However, once they get going, they rock like anyone else. I guess ultimate power is better when rocking so it's better to increase power to max when going 30 odd mph in a tiny gear.
I found this was true when doing standing start ~100m sprints on a road bike. I'd accelerate sort of vertical and rigid for 2-3 pedal strokes then get rocking as I shifted up in speed and gears.
A shorter rider will rock their bike at steeper angles than a taller rider. The bars and seat move back and forth about the same amount for all riders, a little more for a taller rider, a little less for a shorter rider. This means the shorter rider rocks a lot relatively speaking and the taller one very little. Abdujaporov got a reputation for being a swervy sprinter but he simply rocked his bike appropriate for a sprinting 50-51 cm or so bike - his reputation might have been earned on what he did to get to the sprint position, the fact that he sprinted while looking down a bit too much, or that he tested positive a few times for a stimulant used by Soviet fighter pilots.
Since a bicycle stays upright due to slight steering motions, it's much easier to stay upright when working hard by letting the bike swerve back and forth a bit. Rocking the bike allows this to happen naturally.
At slower speeds (climbing), rocking the bike allows you to focus on pulling up hard since you can counter that force when rocking the bike. You can actually feel your hamstrings tensing up as you pull up if you're pedaling slowly.
"...during the Lance years, being fit became the No. 1 thing. Totally the only thing. It’s a big part of what we do, but fitness is not the only thing. There’s skills, there’s tactics … there’s all kinds of stuff..." Tim Johnson