Gravel riding — it’s all the rage right now. Gravel bikes are versatile. A gravel bike on the road is a slightly slow road bike at worst, while a road bike on gravel is a pending incident (even if this incident is just a pinch).
Gravel bikes and cyclocross bikes have a lot in common, but they are definitely not the same thing. Geometrically speaking, gravel bikes move in the same direction as mountain bikes in the ’80s (when they were also fully rigid), while’ crossers’ have a very roadie geometry.
The critical difference between a traditional roadie and a gravel bike is the tire clearance. If only you could put properly wide tires on a racing bike, you could ride gravel with little problem. While modern road frames equipped with disc brakes will accept tires that are much larger than any variant equipped with rim brakes, some even up to 32mm, most gravel frames will swallow a 45mm tire without. to complain. A large volume tubeless tire on a wide rim at low pressure offers much more smoothness for bumps, traction for corners and float on soft surfaces than a narrow tire at high pressure cannot.
I’m not the only person I know to have recently swapped their cross-country bike for a gravel bike. Mine could be 99% used as a commuter bike, but if I want to take an off-road detour, the bike is ready for it. Once you’ve purchased a gravel bike, the most important thing you can change to change the bike’s personality are the tires. There is a world of difference between 700×50 spiked tires operating at 20 psi and 700×28 slick tires operating at 80 psi, even on the same rim.
To help you determine which tires you should use, I present a table of most gravel tires below (as I tried to get them all, experience in these areas tells me that I will have missed something. thing).
To go with the chart, you will find a quick guide to the right type of tire for the location. I have excluded cyclocross tires from the list as they are special purpose and limited by the UCI to narrow dimensions (less than 33mm) which will suit some, but not most, gravel racers.
Most gravel bikes use the same 700c rims as road bikes. A smaller number use 650b rims, which are a bit smaller in diameter and provide room for a larger tire in a space similar to that of the 700c option. In fact, the 650b tires start roughly where the 700c tires end in terms of width, which means the rolling diameter of both sizes is closer than you might think.
… If your 700×40 doesn’t cushion your body enough on the rough surface, see if you have room to go all the way up to a 45 and anyway, try running less pressure…
The total weight of the bike, rider, and equipment being carried is an important consideration for the width of the tire you need. A 40 kg rider with a 10 kg bicycle and no additional equipment can use a much narrower tire than a 90 kg rider on a 15 kg bicycle with 15 kg of bicycle storage equipment.
Some bikers spend 90% of their time on paved roads. Others spend 90% of their time on real gravel. And gravel can range from very smooth to very rough, depending on where you live. The width and size of the button should vary depending on the majority of the area covered. A 30mm wide tire with an almost smooth tread will glide well on roads, but will still handle off-road getaways. A similar 45mm wide slick tire will be almost as good on the road, but much better off-road (or on really broken pavement) for the rider who ventures off the beaten track more often or further.
For those who spend most of their time on the land, a tread is welcome. If your roads are loose but smooth, you can opt for a tire with a tread but narrow (less than 38mm). Most people will appreciate the comfort offered by a wider tire (from 40mm).
There is no doubt that the wider tires provide more comfort. The extra volume of air in the tire allows for lower air pressure, which increases traction and compliance. In tubeless driving, low pressure does not come at the expense of significantly higher rolling resistance, a significant advantage for tubeless.
The bottom line
Road and off-road require competing tire characteristics. The road wants low rolling resistance, maximum cornering grip, high pressure, and resistance to small sharp objects (i.e. broken glass). The off-roader wants flotation, grip on soft surfaces, low pressures for comfort and traction, and resistance to sharp rocks and pinch flats.
The more weight the bike carries and the more time it spends off-road, the wider the tire should be. The tread, especially some corner knobs, can be nice, but the size of the tires is more important than the tread most of the time. You will have to assess your use of the gravel bike, your weight, your experience, your desire to go fast and then experiment a little to find the right tire at the right pressure that suits you.
My bike and I weigh around 110kg and am happy to speed through the gravel around Canberra with a 28mm tire pumped at 90psi. I’ve only had one minus in years – a sharp rock hidden in the gravel – but it’s the uncomfortable end of the spectrum (looks good on the sidewalk before and after chunks of gravel like this) .
If your 700×40 seems really slow everywhere, reduce the size a bit (while increasing the pressure) to find an improved speed. Or, if your 700×40 doesn’t cushion your body enough on the rough surface, see if you have room to go all the way up to 45 and either way, try to apply less pressure. Most people can run safely at a pressure well below maximum pressure for more comfort. In short, don’t be afraid to experiment.
Click below to download the Gravel tire comparison pages from the May / June edition of Bicycling Australia
Comparo Gravel Page 1
Comparo Gravel Page 2
Comparo Gravel Page 3
Comparo Gravel Page 4