Most recently introduced gravel bikes offer the ability to use either 700C wheels (with narrower tires) and 650B wheels (with wider tires). The latter is a very popular option for off-road riding because it offers better traction and overall comfort due to increased tire volume.
But I wanted to find out if this is indeed the case…
There is an increasing trend towards 650B wheels, which are also commonly known as 27.5″. They are advertised as more comfortable and more fun to ride.
A bike with 650B wheels and tires should be a touch more agile in terms of steering, yet at the same time, feel more planted and secure due to the lower bottom bracket height.
On paper, 650B might be a winner… but I was not yet convinced. So I bought a set of used DT Swiss M-1900 wheels (22,5mm internal width) and mounted various 650B tires.
For the sake of this comparison, my vibration results will be using tubes.
Comfort Testing 700C and 650B Wheels
I am vibration-testing two different 650B tires and three different 700C tires on my benchmark bike. The bike is my trusty Jamis Renegade steel with a Lauf Grit SL suspension fork and Redshift ShockStop stem.
I will be using 20 psi in the wider 650B tires and 30 psi in the narrower 700C tires. This is simply because wider tires have a higher casing tension than narrower tires at a given pressure.
The first thing I noticed when I fitted the 650B wheels is that they make the bike have a different feel. The bike feels… smaller. Not much smaller but you can definitely feel a difference.
Subjectively, the wider 650B tires at 20 psi feel more comfortable than the 700C tires at 30 psi. But I was actually quite surprised at how little difference there was between them.
Right, let’s collect some data.
Vibration Testing With Different Rim Diameters, Tyre Widths & Pressures
You can see my vibration measurement procedure & outdoor test courses HERE.
When we examine the level of vibrations across all tires here, the differences are not as large as you’d think. In fact, there is much more variation between tire models than between tire widths. This is really valuable information to know.
For example, the Soma Cazadero (700C) had fewer vibrations than the Schwalbe Thunder Burt (650B) despite a significant difference in both tire width and pressure.
To try and extract something useful from this data, I decided to average out all vibration levels between 700C (30 psi) and 650B (20 psi) to see if I could tease out a trend. This is not particularly scientific but might allow us to say “X rim diameter is more comfortable than Y in this very specific case”.
It turned out that the difference in vibration levels was between 0.6 and 1.8% across all individual tests. That’s not even worth writing about!
One interesting data point is between the 700C Soma Cazadero in 42mm (30 psi) and 50mm (20 psi) on the fast gravel road. In theory, the wider version of the same tire should attenuate more vibrations. And subjectively, I thought the 50mm Cazadero rode more comfortably than anything else. But when you look at the vibration levels, the 50mm had 10% more vibration than the 42mm. This is likely because the tires are simply too bouncy at this pressure and on this road.
I should note that I also tested the 650B x 2.25″ Thunder Burt at 15 psi because it felt a bit too stiff at 20 psi. The tire was still usable at 15 psi, and it was only then that I felt the comfort had increased.
When using less pressure, the data shows that the comfort increased significantly at the front of the bike on the bumpy forest trail (15% fewer vibrations). But I would not want to use this kind of setup on a daily basis as the tire felt soft and bouncy, and it affected the handling too much for my liking.
Summary
The biggest thing that you should take home from this is that the model of the tire is more important than the rim diameter or tire width when it comes to comfort.
I can highly recommend the supple Soma Cazadero tires. Even with twice the pressure of the Schwalbe Thunder Burt, these tires were able to attenuate more vibrations, suggesting that the tire construction is significant in a tire’s level of comfort.
I have some ideas to improve my next 650B vs 700C test, it will be coming up soon…
