ldesfor1@ithaca

this is a question spawned for the sprint photos in a recent post.

What are the pros and cons of rocking the bike so dramatically in a sprint or tough out-of-the-saddle climb?

I know that a certain amount of rocking is nearly unavoidable, but at what point does violently rocking the bike actually begin to rob power from the rider (if at all)?

EventServices

There is no formula. Just go with what gets you there.

Don't try to fight it. You'll rob yourself of more speed if you try to hold the bike straight/upright.

waterrockets 

+1 don't try to hold it steady, and don't try to swing it. Those guys have a serious leg-to-arm strength discrepancy, so they may swing it more than us mortals just because the fight is harder.

JBS103

Would it be to put more body weight over each down stroke or is that negligible?

Compressed

If you do it correctly you can gain a good amount of power from rocking the bike when sprinting. It's a simultaneous push pull and serves to stabilize the core, set the stage for a powerful down stroke, aid the down stroke and to anchor the front wheel.

DannoXYZ 

It depends upon which way you rock the bike. What Compressed mentioned is when you rock the bike away from the power-stroke leg. So if your right-leg is on it's downstroke, you rock the bike to the left. This requires extremely strong arms and back to counteract the leg-muscles. This effectively raises your gearing as it artificially shortens your crankarm-length. I think this is the only scenario where rocking the bike helps.

If however, your bike is rocking towards the power-leg, that is, it rocks to the right as you're stepping down on your right-leg, then some of the leg's power is going into rocking the bike instead of driving it forward. You could probably pull up on the bars a little more in this case.

Compressed

That's exactly what I was referring to, good explanation. This is probably why I haven't completely lost my upper body developed from years of rock climbing.

see



and
https://www.youtube.com/watch?v=Ji_XcHvJvac

carpediemracing 

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.

a rocker,
cdr

carpediemracing 

Note also in the pic of the sprinters - if you draw a line straight down from their torso, it doesn't hit the tire where the tire meets the ground. When you rock the bike, the bike swerves, so the bike stays centered under the rider. The tires move laterally relative to the rider - the bike will seem to pivot at around the BB or so, maybe a bit higher (that's where the vertical line from the rider's centerpoint will intersect with the bike).

Since it is less efficient to move the rider's body back and forth in a sprint (say 150 lbs rider), it's better to move the 15 lbs bike. So the bike gets tossed around (swerves) while the rider's torso goes in a reasonably straight line. His arms and legs are moving but not his torso, not too much anyway.

Great pic btw.

cdr

wfrogge

Rule of thumb..


The stem should always stay inside of the shoulders. Take that pic above and draw a line from the riders shoulders to the stem. it wont go "outside" this line.... ever.

Bullseye

you posted THE VIDEO! god, I love that vid.

-bullseye

waterrockets 

Yeah, that McEwan video is great.

I downloaded it, transcoded it, split out a scene, and slowed it way down. Here's how you swing a bike in a sprint:
https://www.youtube.com/watch?v=1-OOdToL01c

Compressed

Hell yeah!