In a recent white paper entitled Total System Efficiency: Making You Faster, engineers at Zipp put forward the idea that there are ‘five principal impending forces acting on a cyclist… wind resistance, gravity, inertia, rolling resistance and vibration’. To move forward, you must overcome these forces by putting more energy into the rider-bike system than the sum forces acting against the path of travel. So where do tyres fit in? The simple answer is everywhere. However, to find a way into this extremely complex subject, let’s start with that most touted term in regard to tyres: rolling resistance.
‘As a tyre rolls along it deforms and relaxes, resulting in energy loss – that is rolling resistance,’ says Oliver Kiesel, tyres and tubes product manager at Specialized. ‘This is elastic hysteresis loss, which happens inside the compound of the tyre as it rolls through its contact patch.’
As a tyre rolls along the ground it deforms – flattening at the bottom, bulging at the sidewalls – before springing back. As this deforming-relaxing movement happens, molecules inside the tyre compound slide past each other, which creates internal friction, which is energy lost to heat. In theory, wider tyres can limit such losses.
‘If we had a 23mm, 25mm and 28mm tyre of the same type and at the same pressure, rolling on a perfectly smooth road, the wider tyre would offer lower rolling resistance,’ says Kiesel.
This is because the wider tyre has
