Size matters. Or so I’m told.

Like many cyclists, I own a road bike. Well, 3 in fact.  For the purposes of this discussion I can dismiss my olde Claud Butler, as that is on Imperial sized 27 x 1 ¼” boots

My 2nd road bike is a very nice Pinnacle Dolomite, but that’s on 28c tyres for a little bit of comfort and pothole resilience.  It makes a nice fast commuter or day tourer.

Of more relevance to this essay is my Felt road bike.  Just like me, it’s slim, sexy, lightweight and purposeful.  Just like me, I love it.

As standard this speed beast is on 23c tyres.  However, these original hoops are cracking with age and it is now time to replace them anew.  My latest bout of tyre shopping has caused me to stumble on to the latest fashion trend/scientifically led debate (delete as you see fit).


The latest thing is that the fatter 25c tyre are, all things being roughly equal, supposed to actually be faster than 23c tyres.  “Rubbish!”, was my first thought.  How could a fatter tyre with higher rolling resistance be faster?  Well, it might actually be true, and perceived by so many to be true that it has now largely become the norm for tarmac racing.

Yes, like for like they will be slightly heavier than a 23c.  This brings increased inertial resistance to overcome, and factional extra mass to accelerate.  However, the difference is slight, and supposedly the benefits overcome this.  It would seem that, again, like for like, a 25c tyre has a smaller footprint that a 23c.  The footprint is fatter, and therefore shorter as it lifts the circumference of the tyre from the tarmac.  The NET surface area is correspondingly supposed to be slightly smaller, which means less rubber in contact with the road, less rolling resistance.

The extra volume of the 25c means it can be run at slightly lower pressures.  This means extra rider comfort and less fatigue, two of the most important yet most overlooked performance factors in performance cycling.  The lower pressure also gives a better suspension effect, which minimises the way the wheel bounces and loses contact with the road, thus reducing wasted energy

The benefit is supposed to be slight, and may riders report that they can’t even feel any real difference. I am as subtle and sensitive as a low flying sledgehammer, so I do wonder if I will notice the difference.  Nevertheless, the difference is supposed to be genuine, backed up with a small degree of science and testing.

A part of me, try as I might, remains skeptical.  Sure, the majority of thinking riders may have swung that way for their tarmac race setups, but just because a majority do something does not make it right.  Majorities have brought a chap named Adolf to power, brought us Brexit, and at one time even believed the Sun orbited the Earth – just because the majority go for something, it does not automatically make it right.

Nevertheless, my skepticism is also balanced by a healthy curiosity, and a will to believe that there really might be something in it, in much the same way I really would like there to be life on Mars, or that I have half a chance with Rosamund Pike.  Hope springs eternal.  That being the case, I am have opted for a set of 25c’s for the Felt, and I will report back in a future post the results of extensive testing on my butt-dynomometer.  Will I feel the difference, or will I simply be following the trend for no gain?

Stay safe.


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