lyrrad wrote:
Even though the spring rate at ride height is the same, the curve is different as you compress into the tyre.
This will show up on sharp edge features like joins in the pavement.
Here are the measurements I made:
Looking first at the force-deflection response against a flat surface (upper data series):
The non-linear part of the curve is in the lower left, with body weight around 40-50 kgf on each wheel, or roughly 1g (no bump). If I had the original data (not just this photo) I'd be able to zoom in.
Then as the wheel gets more heavily loaded (moving up and to the right), the curves basically straighten out. In the upper right you can see hand notes indicating where tires of different widths have roughly the same slope (stiffness) when inflated to the same pressure.
This is why I mentioned the spring rate depends more on inflation pressure than tire dimensions.
Then at the far right, you can see where each data series bends sharply upwards: force increases and deflection barely changes. This is the flat surface bottoming the tire against the rim. Here the "travel" depends mainly on tire height, not inflation pressure. This is one reason bigger tires are usually nice when your riding surface calls for lower inflation pressures.
Looking next at the force-deflection response against an 8 mm radius edge:
Not much relation, they all bottom out pretty easily!
Damon Rinard
Engineering Manager,
CSG Road Engineering Department
Cannondale & GT Bicycles
(ex-Cervelo, ex-Trek, ex-Velomax, ex-Kestrel)