Monday, March 18, 2013

My cycling in Singapore experiences - Pushing a bicycle up a slope

This is to share my experience and thoughts on how to push a small bicycle up the Braddell road bridge "connecting" the Kallang PCN between Bishan and Toa Payoh. Some background about this bridge can be found here, and here.

First, if you are pushing a full size and heavy enough bicycle, I don't think you would experience much issues. I have been pushing my old skool 26" hybrid bicycle up this place many times. However, I noticed many folding bike riders prefer to carry their bicycle up. I didn't know why until the first time I pushed my 20" Polygon Urbano 3.0 bicycle up this bridge. After doing so a few times, I think I know the issue. Below I'll share my experience:

Typically cyclists push their bicycles by holding the handle bar, allowing them to control the direction.The problem I had when pushing the folding bicycle is that the rear wheel kept slipping inwards on to the steps. This is irritating.

Thus, one way is to have one hand holding the saddle while the other holding the handle. However, with only one hand holding the handle bar, it is more challenging to control the direction.

Anyway, after exploring different ways of pushing, I found that I could push my folding bicycle easily with one hand at a lower position nearer to the frame (see blue arrow head in diagram below). For folding bicycle like mine, I can still control the direction holding here. My free hand can carry other stuff, e.g. my son's balancing bike, so I don't need to make another trip.

Partial force diagram illustration

Then, I gave some thoughts about it and figured out a reason for my method.

When applying force (red solid arrow) at the handle bar position, it creates a torque which is the product of a component of the force applied (red dashed arrow) and the displacement from the pivot point, which is the contact point between the front wheel and the ground. There will be an upward force (yellow arrow) on the rear wheel, reducing the force in between the rear wheel and the ground. This in turn reduces the friction and resulting in the rear wheel sliding down and inward on to the steps. Similarly for the case when a force (blue solid arrow) is applied at a lower position, but the displacement from the pivot point is smaller, leading to less reduction of the friction at the rear wheel.

Thus, I think by applying force at a lower position I avoid the problem of rear wheel sliding. Also, the heavier the rear of your bicycle, the less problem with pushing at the handle bar. Lastly, the problem is also avoided when pushing at the saddle, because there will be a downward force component on the rear wheel, and smaller force component in the torque.

Lastly, one final tip is to position the crank horizontally so that it won't hit the ground when you reach the top of the stairs.

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