Checking the rolling radius -6 July 2008


  1. Experimental description of measuring the tyre compression under load
  2. Links to various web articles

1. Experimental description of measuring the tyre compression under load

Here are pictures of my experimental measurement described in the posting on the course measurement forum

The first is of me loading my bike with my weight while measuring how much closer the front wheel rim gets to the ground:

MCWS on his bike

Below is a picture of the scale showing the pointer attached to the wheel rim giving a reading of 18.4 mm (the zero of the scale was perversely taken as the long ruling opposite the centre of the hole)Under magnification of the original image it was possible to read the scale with a maximum error of about 0.2 mm. I am in position above the bike seat but I have no weight on the seat or the handle bars. I am standing on the books you can see on the floor in the picture above

unloaded bicycle

Now I have placed my weight on the bike and the handlebars in my normal riding position. You see in the picture below that the pointer is now reading 14.5 mm. The tyre has compressed by 3.9mm under my weight. If you look where the tyre is touching the ground, you can see that in the picture below (under load) the length contact point with the ground is decidely longer than on the unloaded picture above. (The two pictures are at exactly the same magnification.) It would be rather difficult to see the actual contact patch unless one were to photograph from below through glass.

loaded bicycle

An interesting experimental note is that during the setup we had the tyre and scale resting directly on the floow which is a slightly cushioned type of plastic floor covering. Our first reading of deflection under load was only 1mm. Presumably the bike wheel was deforming the floor covering! We sooned fixed that by placing a rigid bit of chip bopard (the white rectangle you can see in the top photo) on the floor and placing both the bike tyre and the scale on this firm base.


2. A collection of links

Page last updated 8 July 2008