This post is entirely unplanned. I was actually just messing around with Veloviewer and noted the info depicted below and decided to post something. I’ve been thinking about 650b and how it’s currently being sold for several months and I have some ideas and now some data as well.
If you hear 650b x 42 tires are as fast as a road racing tire in 23/25/28mm you’re not getting the full story.
The 650b tires may roll as fast when there is no pedaling but I think there are significant losses from pedaling as well as from the aerodynamics of a 42mm wide tire. I have performed no rigorous testing, I just went out and rode my bike each day. The image below is from my riding in exclusively in 2015. The comparison should really be between the regular 700c DX and the 650b DX but I liked how close the GTR and 650b DX were so that’s where I put the arrow.
There are 3 key players.
The DX; a disc brake cross bike ridden with 700 x 28 Forte Strada Tires (specs here), note that I rode this bike equipped with fenders (specs here) but do not have a picture. Tire pressure used was between 75-85 psi.
The GTR; a road bike ridden with 700 x 23/25 Continental Grand Prix (specs here) tires. Tire pressure used was between 80-100 psi.
The DX was equipped with 650b x 42 Grand Bois Hetres (specs here) tires. Tire pressure was generally 35-50 psi.
I rode all bikes with the same two water bottles and same saddle bag. The vast majority of my riding was on the same roads around the metro Atlanta area. I didn’t do any group rides in 2015 and none of the races I did are present in the data from Veloviewer.
So, for me, switching to 650b was worth exactly 0.5 miles per hour. A little more than 3% difference in average speed. About an 8% difference in time/miles ridden. If I were riding specifically to go fast or to go as far as efficiently as possible I would not recommend the 650b tires.
However, I think overall 650b is the best choice for a given recreational rider. The tires have had several advantages for me. They are significantly more comfortable to ride, both in how they feel while actually riding and the after effects of the ride. I had moderate piriformis symptoms all spring while riding the regular DX that vanished after I switched to the 650b tires. Like literally no issues after my next ride when I had previously been experiencing the issue within 2-3 hours of the end of my ride on the 700c DX.
The Hetres are also significantly safer than narrow racing style tires. The width helps maintain control over poor road surfaces, allows more control while experiencing a flat tire at speed and contributes to better traction on both wet and dry roads. They also allow riding on pretty much anything that can be qualified as a “road.”
Speaking of flats, the tires are also not nearly as resistant as espoused in BQ. I’ve had 6 flats in 3200 miles or so. This is a significantly higher ratio than any of my 700c bikes ever. The issue is that unless you are vigilant with checking the tires wearing a headlamp and peering into every tiny cut there are pieces of glass that get embedded in the rubber and slowly work through until they puncture the tube.
So this really ended up kinda rambling but I guess the point is that I rode 3 bikes and the 650b equipped one was slower.