Road tyre widths: 23/25/28c – Which one should you choose?

If you, like many others, have taken your eyes off the changes in cycling technology for what seems like no more than a few minutes, you’ll be glad to know that your tyres and wheels are probably outdated. For years, everybody rode 23c, then suddenly we’re on 25c tyres with 28c tyres already on the horizon. But before you go out and buy a fat road bike to get ahead of the curve, you need to ask yourself a few things. Why is this happening, does it actually make a difference, and should I make the swap?

For a few years now, there has been research suggesting that slightly wider tyres might be faster than skinnier variants. However, any implementation of this was significantly hampered by the technology of the time – both rim brakes and wheel width prevented wider tyres. On top of this, the last few years have seen a drastic shift in the mentality surrounding cycling. More and more people are demanding do-it-all bikes, rather than sub-specialised bikes you can only ride on Tuesdays before a full moon. People want to explore more and leave flat tarmac far behind. Wider tyres are the easiest way to convert any bike into an all-day gravel grinder. Wider tyres also provide increased flat protection and provide far superior comfort, at no real added expense.

But for the racer, none of that really matters, does it? We want to know how to get from point A to B in the fastest possible time. For those who don’t care about the physics, the answer is a 28c tyre. They’re said to roll up to 4 watts faster at 40 kilometers per hour. Arguably more importantly is that with a wider tyre you’re less likely to get flats, and saving one flat will save you more time than minimising rolling resistance ever will.

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The Continental Competition, in a 25c, is the choice of many Grand Tour professionals.

Rolling resistance is determined by a number of factors – not only how much of the tyre is in contact with the road, but also the distribution of tyre that is in contact with the road. Perhaps counter-intuitively, the contact patch of a 23c and a 28c tyre is the same, but it’s the shape of the contact patch that differs. A 23c tyre has a long, narrow patch, whereas wider tyres have a short, wider footprint. A longer, narrower patch means that more energy must be expended to deform the side wall of the tyre, and this energy that’s going into the side wall of the tyre is not going into propelling you forward. Because a wider tyre has a shorter distance of side wall to deform, that means more energy is being transferred straight onto the road, meaning you’ll get from A to B in a faster time.

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This diagram from Continental nicely sums up the changes in resistance with increasing widths.

Before you go out and buy the fanciest 28c tyre you can find, it’s important to know that to fully experience the resistance benefits of a wide tyre, you need a wide profile rim that maximises the profile of the wide tyre. That means if you’ve been riding on 23c tyres and associated rims, if you just slap on some 28c tyres, it won’t roll faster than your 23c tyres. However, you will still get more comfort, grip, and less punctures.

You might have seen the videos of people testing different tyres and finding minuscule increases in speed with wider tyres. You can generally take these with a grain of salt, as none of the tests come close to being scientifically rigorous, and any data generated from them is unlikely to be statistically significant. To date, there has not been any double blind, placebo controlled trials of tyre widths and the impact they have on real world speed. However, the theory is sound. So if you want to save every possible second, the wider tyre might help, but if you’re after more comfort, grip and puncture protection, then swapping to a wider tyre is going to be the right choice.

About Tim_Davis@Pushys

I'm a Science Graduate and Medical student at the University of Queensland, specialising in anatomy and physiology. More importantly, I'm all for any type of riding; road, mountain, dirt jumping, I love it all! Let me know if there is anything you want to know about nutrition and health, and I'll do my best to help you out!

3 Responses

  1. Stevo

    Interesting the move to wider tyres. Do you have a reference to 4w @ 40kmh statement?
    That image of the tyre looks like a Conti, not a Maxxis as in the caption.

    Like

  2. I first noticed the value of wider tyres for a heavy load in the 1980’s. On my old 68cm framed tourer I was slower on slick 27 x 1″ (25c) tyres than a 27 x 1 1/4″ (32c but more like a 35c) Michelin World Tours. I put it down to the extra air in the tyres absorbing the bumps that the steel frame couldn’t cope with.
    Now I run Schwable 28c tyres at about 85-90 psi. Continental Grand Prix 4000 28C tyres measure 30.5mm, which is too wide and tall to fit my old Trek Domane frame. Newer Domanes have more clearance.

    Like

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