Halfway through a long gravel loop, the route leaves the farm roads and drops into a forest trail: roots, loose stones, a few sandy sections. On 40 mm tires, still at the pressure you set for the tarmac to the start, the bike starts skipping sideways and every hit comes straight through the bars. You back off, not because your legs are empty, but because the bike stops feeling planted.
That moment is where the 650b question usually starts. Not as a trend, but as a practical one: can I fit more tire, and what do I give up?
Same outer diameter, more tire
A 650b rim has a bead seat diameter of 584 mm, compared with 622 mm for 700c. That 38 mm difference is space you can fill with tire. Mount a 2.1″ (about 53 mm) tire on a 650b wheel and the total diameter lands within a centimetre or two of a 700c wheel with a 40 mm tire. For most gravel frames that means bottom bracket height and handling stay close to what you know, while the air volume goes up considerably.
That is also why many gravel frames built around 700c x 40–45 mm list 650b x 2.1″ or wider as an alternative. Always check your frame’s clearance with the manufacturer: the width at the chainstays is usually the limit, not the diameter.
What more air actually does
A wider tire can run at lower pressure for the same support. Lower pressure lets the tire wrap around stones and roots instead of bouncing over them. You feel that in three ways:
- Grip. A larger contact patch holds on loose corners and on climbs where a narrow tire starts to spin.
- Comfort. The tire absorbs the small, constant vibration that wears out your hands and lower back over a long day.
- Protection. More volume between rim and ground means less chance of a pinch flat or a rim strike on a sharp edge.
The trade-off is real: a 2.2″ tire weighs more than a 40 mm tire, and on smooth tarmac it rolls a little slower. If most of your riding is fast, smooth gravel, 700c is still the more efficient choice.
The rim matters as much as the tire
A wide tire on a narrow rim behaves like a balloon on a stick. At low pressure the sidewall folds over in corners and the tire feels vague. The internal rim width is what gives a wide tire its shape. For 2.0″ to 2.4″ tires, an internal width in the high twenties supports the sidewall, so the tire mounts broader, keeps its profile when you lean the bike over, and deforms less under load.
That is the thinking behind the Anath 650: a 27 mm internal hookless rim, sized for exactly this tire range. Our ART asymmetric profile evens out spoke tension between the drive and non-drive side, which keeps the wheel true when it carries a loaded bike over rough ground.
Who gets the most out of 650b
650b gravel wheels make the most sense when the route decides for you:
- Bikepacking and multi-day trips, where the bike is heavier and comfort over hours counts for more than speed over minutes.
- Routes that mix gravel with singletrack, roots and loose climbs.
- Riders who want one bike that handles rough terrain with more confidence, without buying a mountain bike.
If your riding is mostly fast gravel roads and the occasional race, a wide 700c rim is the better match. The Anath 423 SL uses a 33 mm internal rim for tires from 40 mm, and the SandStone SL goes wider still at 37 mm internal.
A second wheelset, not a second bike
Many riders end up with both: a 700c set for fast days and a 650b set with big tires for the trips where the road ends. With the same thru-axle standard and Center Lock rotors, swapping takes minutes. Use the same rotor size and a similar cassette on both sets, and the bike needs little more than a quick check of the brake alignment.
Want to see the details? Take a look at the Anath 650 in our webshop.
