Almost any recently introduced gravel bike offers the ability to run both 700c and 650b wheels. The latter is a very popular option especially because it should offer better traction and overall comfort due to increased tire volume. I wanted to find out if this is indeed the case…
There is an increasing trend towards 650b wheels. They are advertised as more comfortable and more fun to ride. The bike with 650b wheels and tires should be more nimble and alive, yet at the same time more planted and secure due to the lower BB and wider contact surface. So on paper, this is a winner but I was not convinced. So I bought a set of used DT m1900 650b wheels (22,5mm internal width) and mounted on them a GravelKing SK 48 mm tires. I tested them both tubeless and tubed but for the sake of this comparison, I stayed with tubed version.
How does 650b ride?
The first big revelation with 650b wheels and tires is a different bike feeling. It feels… smaller. Not much but you definitely can feel the difference. So the bike is also more nimble but again, the difference is not that big. If I need to compare the feeling with let’s say a 700x50c setup I would say that while 700x50c feels like riding a big tanker the 650b 48 mm is much more like riding a tank. Small, very nimble but a tank. This means that you immediately start to behave like a hooligan on a bike with smaller yet wide wheels. You stop looking for the bumps and just hammers through everything. So yes, 650b can be more fun, but is it also more comfortable? Subjectively yes, but this is no magic carpet ride, especially at 30 psi tire pressure. And it can’t be really because at 30 psi you have more air in the tire (comparing to a 700x43c tire) and thus it will be stiffer. But you don’t buy 650b tire to run it with a relatively high pressure (with 700×43 you don’t have really a choice but with 650b you can safely go as low as 20 psi to really feel the benefits of a bigger tire).
So how about 650bx48 at 20 psi?
Yes, this is much better but still no magic carpet ride. And with that kind of pressure, you can start to feel some tire movement and definitely you feel slower on pavement than on a Panaracer GravelKing Sk 700×43 tire with 30 psi air pressure. So 20 psi is better in terms of comfort but how much better? My measurements show a 12,2% improvement (versus the 700×43 size with 30 psi air pressure) at the front and very modest 1,8% at the back (forest bumpy road). On a fast gravel track, the difference between 650b at 20 psi and 700c at 30 psi was again 12,8% at the front and a slight decrease in overall comfort at the back (3,3%). So, in general, 650b tire is better, yes?
Let’s compare 650b with a more supple 700c tire.
Panaracer GravelKing SK is not the most supple tie yet at a very low air pressure like 20 psi it starts to behave like one so to make the comparison more interesting I also tested it against a very supple 700c tire which is a Soma Cazadero in 700x42c variant run at 30 psi. This time the comparison both subjectively and objectively goes in the favor of a 700c tire. Riding on the bike feels just better – it is no tank but simply a very comfortable, yet still a fun ride. And the data shows it: on a bumpy forest road, Soma Cazadero 700x42c was 4,3% more comfortable than Panaracer GravelKing SK 650bx48 tire at front of the bike and 5,5% at the back. On a fast gravel route, the 700c tire was still 3,3% better at the back and exactly as much comfortable as 650b at the front (no difference there).
Now it is time to go even wider with 650b!
For now, it seems that a supple 700c tire is better than a 650b one. At least better than a Panaracer GravelKing SK tire. I would really want to have an opportunity to compare 700c with 650b wide Cazadero tire but until Soma introduces a 650bx50 variant I had to look for other solutions. Based on people’s opinion I found that Schwalbe Thunder Burt should be a good choice and thanks to a huge tire clearance of my current Lauf Grit SL fork I went with the biggest possible variant: a 2,25 inch one! Naturally, I could mount this tire only at the front of the bike (at the back was still a 650bx48 GravelKing SK tire) so I measured only the front end vibrations. But before showing the data lets talk about how the bike felt with so wide front tire… No surprise there. It felt like a tank. But not a very comfortable one. At least at 20 psi air pressure (again this was the result of the amount of air in the tire at the comparable psi – the more air the stiffer the tire). So to get most of this big tire I went even further and lowered the air pressure to 15 psi. It was still usable and only then I felt that comfort has increased. But to be honest I would not want to use this kind of setup on a daily basis. The tire felt too soft and bouncy and it affected the handling too much for my liking. But the data shows that at 15 psi air pressure the Thunder Burt 2,25 was 12,1% more comfortable on the forest route than Cazadero 700x43c at 30 psi. But on a fast gravel route, the bounciness of the tire showed its bad side and the level of vibrations increased about 10,6%. At 20 psi Thunder Burt was less comfortable no matter the test route.
Can we go even further?
At that point, it seemed that the 700cx42 tire was the best solution. Of course, I could lower the air pressure to 20 psi to gain even more comfort but as I said earlier it would compromise too much the handling of the bike and result in a pinch flat right away (tested and confirmed). But how about putting a 700x50c Soma Cazadero in front of the bike? Again, thanks to a Lauf Grit SL huge tire clearance I could do that and… I did that! Boy, it felt weird… But it was a nice weird feeling. Subjectively I enjoyed this setup the most (mostly because it somehow combined the tank but fun feeling of a wide 650b tire with the overall nicer feeling riding on a bike and not being on a quad, that can be associated with a 650b tires). So in my head, I was already seeing the great improvements in the comfort (compared to a 700x43c tire) and I thought I found the winner. Yet my objective measurements showed that the bigger tire was more comfortable only on a bumpy forest road and only by modest 2,3%. On a fast gravel route, the bigger tire was more bouncy and this resulted in a 10,6% increase in vibration level (the same result as with Thunder Burt 2,25 run at 15 psi tire pressure).
So we have a winner?
Based on my current measurements I can say that a bigger / wider tire trend is indeed beneficial in terms of overall fun factor and although subjectively you can feel more comfortable, objectively going for a bigger tire is not the best choice when the comfort is your priority. To be honest this was a shocker for me because I really (wanted to) believe that bigger is better. But this is not the closed case. As you may already notice I run all the tests based on my benchmark bike equipped with a Lauf Grit SL fork, a suspension stem from Redshift Sports and an Ergon CF3 flexing carbon seatpost. Those elements for sure influenced the overall results so in part 2 of this comparison I will rerun all of those tests but this time with a rigid bike (rigid for, no suspension stem or suspension seatpost). This could be interesting (excluding a Thunder Burt tire for obvious reasons). But for now, a Soma Cazadero 700x43c with a 30 psi air pressure stays on my benchmark bike as the most comfortable and most enjoyable tire solution currently available…