Why is it easier to balance a non-moving bike standing up than sitting down?

Question

When I arrive at a traffic light that is red I usually just stop the bike, stand up and balance it for a minute or two before going on, without ever putting a foot on the ground. Learning to balance a bike like that was easy, I estimate it took less than hour before I could stand indefinitely (well, the static load is quite high so I probably won't stand more than 5-10 minutes due to exhaustion). With some effort and luck I can also release one hand.

BUT, now I have tried to learn to balance the bike sitting down on the saddle and that is basically impossible. Why is that so much harder? Any hints on how to do it?

Answer 1

Just speculation, but I suspect that when we balance standing up, we move our hips laterally to make fine adjustments to the relative position of our center of mass over the wheels. When doing so, we push laterally from our feet on the pedals, which are low enough and far enough below the center of mass to make adjustments relatively easy to accomplish.

With your backside planted on the seat, the main mechanism to laterally adjust your center of mass is to move your shoulders and chest relative to your hips. Now you have a smaller mass on a relatively short lever anchored relatively high up. So a movement of the shoulders mostly results in a countermovement of the hips in the opposite direction. That makes it not only fairly difficult to get much movement of the center of mass relative to the wheel-ground contact, but also difficult to do so in a controlled manner.

Answer 2

Your centre of gravity (CoG) aka centre of mass (of you + bike) is balancing over the contact patches of the tires. In fact, over the line connecting the two patches.

Standing up raises your CoG higher up which helps some (try balancing a broom on your palm head-end up vs. handle-end up). A longer pendulum tips more slowly.

But much more importantly, having your butt off the seat lets you shift your weight sideways much further and faster. You're pushing sideways on the pedals (and some handlebars but mostly pedals) to do this.

This applies a sideways force to the ground via your tires, and an equal and opposite net force on your centre of gravity. So you can apply a centering horizontal force on your own CoG, letting you get it back over the balance point on the ground.

It also lets you tip the bike, moving some close-to-the-ground mass one way, and your torso the other.

If you start to tip left, you tip the bike more left, but move your body right. The centre of mass of the whole you+bike system moves to the right, because you were able to push sideways on the ground to make that happen.

If all you could do is lean your shoulders (because your butt is stuck to the seat), that's not helpful because you're moving a high-up part of your body.

The lever arm from pedals to ground is short, far below your CoG. I think this is relevant to being able to generate horizontal force on the ground. Tipping the bike left/right levers you sideways, like moving your palm under a broom handle that you're balancing. (I think).

Answer 3

I think it's mainly harder because there are more contact points between you and the bike, and the one in the center, your seat, makes the system a lot more rigid. Which makes it harder to shift weight around at the crucial moments which is what balancing is all about. Also when standing up you can do things like push the bike left/right while your body stays roughly in the same position which is pretty much impossible when sitting, because you'd be moving your body at the same time as the bike.

As for hints: start on a small slope without engaging brakes but using pedals to allow the bike to move forward by pushing the pedal and backward again by releasing some pressure. Apart from sticking out elbow/knees this allows more movement to counter the bike (and you) trying to fall. But that's about all you can do so for the rest: practice, practice, practice.

Answer 4

Balancing is done by shifting mass in a way that your centre of gravity is opposite to the side on which you are currently falling.

• When sitting, you can move the upper body and head by bending your spine but this movement is restricted to about 20 cm, and still involves only about half of your mass. Your centre of gravity will move by only half of that distance (10 cm), which gives a correction range of +/- 5 cm.

• When standing, you can easily move your entire body (except the lower legs and hands which must remain on the pedals/handlebar) by half a meter. Your centre of gravity will move by about 80% of that distance, (40 cm) with a correction range of +/- 20 cm.

If you lean 5cm to the side at the CoG level (10 cm at head level) while sitting down, it will be very hard return to equilibrium. While standing, you can easily return to equilibrium even from a 10 cm tilt.

Answer 5

When you're standing, the pedals are effectively the endpoints of two torque arms in the shape of a small "v". It's reasonably easy to adjust the amount of force applied to either by shifting your entire weight via your legs. When you're sitting, your weight comes to bear largely on the seat, creating a longer (single) torque arm that is more difficult to counteract. The principle agent, then, would be applying your upper body weight to either handlebar. Simply leaning in either direction would not oppose the torque arm once it were no longer vertical.

Answer 6

Also, two other effects:

1. When standing, it's much easier to apply different levels of force to each pedal. You can even pull up on one pedal if you're clipped in. That will make balancing while standing on the pedals easier.

2. When seated, a large amount of your mass will move with the bike - if the bike starts tilting left, your bottom half is going to move to the left with the bike. That will make balancing while seated harder.

Answer 7

I agree with Andrew's comment, and would add this: typically we trackstand by pedaling into the road crown, and letting the crown push us back. It is much easier to maintain force on the pedal when standing than when sitting.

Answer 8

I think this should be on physics stack exchange for an explanation. It's not exactly 'center of gravity' as @Nelson said, but you have to think about where the forces are applied. When sitting, most of the force is applied down onto the seat, and the rest to the handlebars, and this is transferred down to where the tires meet the ground. If you begin to tilt to a side, the bicycle seat is now on that side and most of the force is off to that side, tending to increase the tilt in that direction. If you try to lean to the other side to counter that, the force of your body moving actually initially makes the tilt in that direction worse as the opposite reaction is pushing the bicycle seat that way when you lean the other way.

When standing on the pedals, you can shift weight more easily from side to side, but the main difference is how low your feet are. Now you have a low point with most of your weight on it and a high point to use to tilt the bike: the handlebars. You can apply weight easily to either side using your feet and use your hands to move the top of the bike from side to side. In a sitting position you lose most of the downward pressure on each side from your feet and you are basically unstable. When standing if the bike tilts left you put more pressure on your right foot and pull on the left handlebar to get it vertical again. What move would you use when sitting to accomplish the same thing?

Answer 9

Unlike most answers assume, you can't laterally move your center of gravity when balancing on a bicycle, because there is nothing to brace against. Instead, the balance is maintained by moving the contact patch so that it is under the center of mass or just enough to the side to tilt the bike and ride in desired direction like an inverted pendulum (the "movable weight on a stick" mentioned in a comment). When the bike is moving, this is done with very small steering movements.

In a normal trackstand, the bike is held in place with front wheel at angle so that the contact patch can be moved left and right by going a bit back and forth. This is easier to do when seated, but not what the question is about.

The other way to move the contact patch is to tilt the bike. Because the tires are not a knife edge but have a round profile, they roll a bit laterally when the bike is tilted, just enough to move the contact patch. The center of mass of bike and rider does not move much, because there is nothing to push against. If the bike and rider were very close to balance when the movement started, this can be enough to maintain balance. Other forces that have very small effects are torque from deforming the tire and rotational inertia of the tilted bike. This trick requires that the bike can be tilted without the rider - which is possible only when standing up.

Yet another way to move the contact patch is to twist the handlebars. A video that shows all three techniques in action can be found here.

Answer 10

I think it's easier, since you can move more. Sitting down, you are limited to shifting your upper body abit which EASILY throws you off balance. But if you stand, you can eversoslightly move your hips, you can tilt left and right without shifting your entire body weight to either side.

I can't tell you why or if you are more stable standing up, but is way easier balancing because of what I explained above.

Answer 11

If you want to balance sitting down, just spin your cranks backwards, works for me.