On tyres and their diameters

Tyre width is an important aspect to think about, and opinions vary on the subject, with two rather polarized camps. You get the weight weenies that are running those skinny pencil-thin tyres (usually 23mm – and this diameter can even get lower!). They run them whilst claiming that thin tyres roll faster due to less friction on the road, or some similar excuse.

This has been proven to be a myth, and in fact wider tyres roll faster because of a reduced tyre casing deformation and hence a reduced loss of energy. Detailed info can be found here:¬†http://www.bikeradar.com/gear/article/bicycle-tires-puncturing-the-myths-29245/ The same is true for larger tyre/wheel combos, bigger tyres/wheels roll faster too. 29″ tyres roll faster than 26″ tyres.

I am definitely in the camp of bikers who like to run fat tyres on our bikes. Fat tyres provide comfort, they have TONS more grip on the road. Ask anyone, ask your nan, even she knows! I recently acquired a pompino, which has a more aggressive riding position than my other bikes, and running the fattest tyre that I can find helps with the amount of shock travelling through the handlebars and into my hands and wrists. Not to mention – running a fat tyre means that I don’t need to worry about my front tyre skidding out sideways from under me as I take some of those aggressive turns. And I DID have a couple of wobbly moments where this happened using the original tyre that came with the pompino.

On the weekend I changed the original tyre (Vittoria Randonneur Cross Pro 32mm) for a fatter tyre I had lying around (Innova 40-622). The main reason I changed the original tyre is that despite it being advertised as a 32mm diameter tyre, on my rims (which has 13.6mm internal width) the tyre actually measured 28mm in width:

Vittoria Randonneur Cross Pro 32mm

Vittoria Randonneur Cross Pro 32mm only measures 28mm on 13.6 mm rims

The Innova tyre, which is marked with ETRTO (which is meant to be the most accurate system) of 40-622 actually only measure 34mm on my rims:

Innova 40-622 tyre

Innova 40-622 measures 34mm on 13.6mm rims

Now, I can tell you that riding the Innova tyre feels really very nice, despite the fact that the tyre came free on a Halfords bike. It is much more sure-footed, as well as absorbing shock very well, providing me with a sort of front suspension.

Another thing to keep in mind is that in a similar way to clothes and shoes, not all 35mm tyres will actually measure 35mm. Some will be much thinner in order that the manufacturer can boast a lighter 35mm tyre, when in reality they’re flogging a 32mm tyre as a 35mm. All about this here (http://sheldonbrown.com/tire-sizing.html) The best indication of tyre size is usually given by the ETRTO sizing, which looks like this: 622×40 which denotes a 622mm bead circumference (i.e. 700C wheels) and a 40mm tyre diameter. For mountain bikes, the ETRTO sizing is 559×40 (for example). The 559mm part will stay constant, as that is the bead diameter for a 26 inch mountain bike tyre.

So, if you want to ride more comfortably, on tyres that give you better grip, more suspension and generally a safer/better ride, then I would suggest that you consider some wider tyres when the time comes to get some new ones. Or, in fact when you’re looking for some nice winter tyres, they’re really great on wet roads and those rotting leaves.

Some things to look out for:

  • The real tyre diameter will depend on the size of your rim (as shown in the pictures above)
  • The real tyre diameter will also depend on the brand which is making the tyres. I find Schwalbe to be quite honest in their sizing.
  • Make sure you have the clearance in your frame for a wider tyre. Some road frames are limited to 23-25mm.
  • Check the internal width of your rim and don’t go over the maximum tyre width recommended for that rim.

Go on, try some wide tyres!

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