It’s not about the bike (tyres) … or is it?

In my teens, I remember the aim was very much to have the thinnest tyres and push the highest possible gear – that was manly cycling! I still have to remind myself sometimes to knock down a gear or two and get the legs spinning – but now I’m also told that I should also be forsaking my skinny tyres.

The science is a bit baffling (not helped by not being entirely consistent) but the consensus seems to be that wider tyres have generally lower rolling resistance at the same pressure, compared to narrower tyres. I’ve seen a suggestion that a 25mm Continental GP4000 s2 tyre at 109psi has about 1.4 watts advantage over its 23mm brother. A lot of pro teams have gone to 25mm tyres and that tends to suggest the science is good.

I don’t have a power meter but Strava estimates my maximum output to be about 320 watts. That is about 5 watts/kg which is certainly OK – and would be positively good if I could maintain it for more than a few minutes … which I can’t.

Assuming the power is in the right ballpark, for a pair of tyres the power saving it is the best part of 1% of my maximum output. If the saving is constant (I don’t suppose it is) it would be closer to 2% of my average output on a more gentle ride. Some of the power saving can be traded in for a smoother ride by taking out some air form the fatter tyres (a smoother ride itself almost certainly being a faster ride) so the options are certainly attractive.

Although there are small weight and aero disadvantages they would be trivial in comparison – so switching to 25mm tyres seems to fall squarely into the category SNT (silly not to). Indeed, it is probably the category FSNT.

The tyres on my sportive bike are nearly down to the wear indicators and I have a slow puncture in the front so now looks like a good time to change. I have new 25s (Continental GP4000 S2s) so here we go to another silver bullet of faster cycling!

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