Table of Contents
This is the last article in the 700C vs 650B wheel-size trilogy.
The second test was all about using a rigid bike without any comfort-improving parts. I tested two different tire models, in two different widths, on two different wheel diameters.
For this last test, I’m focussing on one tire model only – the supple Soma Cazadero. I’m testing it in three different widths and on two different rim diameters.
And now, I am ready to tell you once and for all if you should ride 700C or 650B.
Summarising My 700C vs 650B Tests
The first test ended without any conclusive results. Essentially, the test showed there is much more variation between tire models than between tire widths (or rim diameters).
But I still really wanted to know how the supple Soma Cazadero tires would compare in different widths and rim diameters. So, I got my hands on Cazaderos in 700C x 42mm, 700C x 50mm, and 650B x 50mm.
The Bike Setup
I am currently testing a Canyon Grail SLX 8.0 ETAP gravel bike and decided to use it for this wheel size comparison.
I was only measuring the front-end vibrations. To make sure that the rear of the bike was not influencing the results in any significant way, my rear tire was always a 700C x 40mm Schwalbe G-One Bite (25 psi). And I used a Redshift ShockStop seatpost that helped prevent my body from bouncing.
I used the carbon DT Swiss GRC 1400 Spline wheels for the 700C test, and alloy WTB Asym i23 TCS wheels for the 650B test. Both wheels have rather wide inner widths (24 mm and 23 mm respectively) so the tires could be inflated properly.
But to my surprise, none of the 50 mm variants were actually 50mm wide. They were 47mm in both cases, whereas the 42mm tire was 42mm on a carbon DT Swiss rim.
The tires were set up tubeless to make sure that the inner tube is not influencing the results in any way.
Setting The Tire Pressures
I again set the correct air pressure based on Laplace’s law (read about it in detail in comfort test #2).
The 700C x 42mm tire was run at 25 psi. The 700 x 50mm tire was run at 21 psi. And the 650B x 50mm tire at 21,5 PSI (because it has slightly less air volume than the 700C variant).
Vibration Test Results
You can see my vibration measurement procedure & outdoor test courses HERE.
For those who have followed my work for a while, there will be no surprise that the right tire construction is crucial for riding comfort. Essentially, the more supple the tire construction, the better the overall comfort.
The supple Soma Cazadero tire diminishes the vibration differences between 650B and 700C wheel diameters. When you compare the results, you can only really see a steady decrease in vibrations between different tire widths, not wheel sizes.
This is especially the case on the bumpy forest trail where you only get 3% fewer vibrations when switching from 700C x 42mm to 650B x 50mm tires. And on the fast gravel route, it’s a bit more, but still only a 6.5% difference in vibration attenuation (in favour of the wider 650B tires).
The difference in comfort between tires of the same tire width (50mm) saw just a 2.5 to 3.5% difference on the two test tracks – favouring the 700C tire over 650B.
The biggest improvement was when switching from 42mm to 50mm on a 700C wheel. On the fast gravel road, the wider tire had 9% fewer vibrations. And on the bumpy forest trail, it was a 6.5% difference.
There is certainly a case for wider tires if your bike can handle it, and the terrain you ride demands additional comfort (faster, rougher roads).
I will stay with 700C wheels with 40 to 45mm tires because I think this is the best combination of rolling characteristics and overall comfort (when using supple tires).
Of course, 650B has the potential to be even more comfortable because there are now gravel bikes that can fit right up to 60mm (2.4″) tires. But let’s be honest here: you would have to run a 60mm tire at 18 psi to achieve the equivalent casing tension to those in this test. In my opinion, this kind of low tire pressure compromises the steering a bit too much.
Overall, I don’t think the minor difference in comfort between 42 and 50mm is worth it for the terrain I ride. Especially, when using the Redshift ShockStop stem and Redshift ShockStop seatpost, where I’d have a hard time noticing any differences between tires (in terms of comfort).
A supple 700C x 40-45mm seems to work best for my use case.
You can support the CyclingAbout Comfort Lab by purchasing Soma Cazadero tires on Amazon. Simply click HERE for 700Cx42mm, HERE for 650Bx42mm, and HERE for 650Bx50mm – and a small commission will come our way.