We've seen a boom in 650b wheelsets and tyres over the past couple of years, fueled by the rapid growth of gravel/adventure cycling. These smaller diameter rims allow for larger volume tyres, or more compact framesets, or a combination of the two.
So, which is the better option? Many recent frames will accept either size. Dan, our lead Bike Fitter, takes a look from a bike fit point of view:
700c has been the standard for as long as modern road bikes have existed. However, with the recent boom in gravel bikes, handling and compliance are increasingly important considerations when purchasing a bike.
There are certainly benefits to running 700c wheels; primarily greater momentum and lower rolling resistance. However, the smaller 650b standard is a good choice for riders who prioritise grip and compliance, and who want to gain additional comfort from higher volume tyres, rather than prioritising flat out speed.
If outright top end speed is the goal, the bigger wheel is better (it's why elite mountain bikers still prioritise 29" over 27.5"). But for anyone looking for the 'fun factor' from an assured, comfortable handling bike, 650b should be a strong contender.
below: Cervélo's Áspero is part of a new breed of gravel/adventure frame that'll happily accept either 700c wheelsets for speed and longer road routes, or 650b for fatter tyres/bigger air volumes on more extreme terrain.
There's another benefit to running 650b wheels that's come about with the rise of gravel bikes - better geometry for smaller riders.
To use the mountain bike example above - Elite mountain bike riders want maximum speed, but subsequently the lengths the smaller riders have to go to shoehorn themselves onto a larger 29" wheeled bike is crazy.
As an example, 5ft 2in Emily Batty's Trek Superfly, seen here back in 2014 when 27.5/650b started making inroads, was still running 29in wheels, and the compromises required to make it fit are clearly visible. Nowadays Emily has a choice of Top Fuel or Pro Caliber - but both are in 27.5in form!
Smaller wheels allow multiple benefits in bike geometry. Less toe overlap and lower tube top tube height for improved stand over are two big factors that relate to a riders confidence. Plus unlike smaller frames on 700c there is less need to slacken the head angle and increase fork rake (which in turn, equals better handling on 650b).
This means for smaller riders who've had issues with comfort or handling of bikes (and in mine and many other bike fitter's experience, that is nearly every rider under 5'4) 650b presents a great option for both gravel and road riders. It's worth noting this has only become a realistic option as more tyre and wheel brands offer 650b choices, but nonetheless it now presents a genuine option for riders of all disciplines.
There is still a perception that small = less. But I guarantee that once you ride a 650b bike off-road, or if you've struggled with handling on small bikes previously, 650b will offer you the most fun and confidence you've ever had on a dropped bar bike!
Nearly all of the bike and wheel brands we partner with at Bespoke Cycling offer 650b options in their range. Get in touch to discuss your next build, and whether 650b could be an option for you on a new or existing bike.
below: The OPEN WI.DE. is another firm favourite that'll run either 700c or - as seen here - 650b wheelsets. The smaller 650b rims mean there's more room for super-chunky tyres like these 2.35in wide Schwalbe Rock Razors - giving tons of grip and loads of cushioning.
For many more examples of the WI.DE.'s versatility, check out our Build Gallery
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Cervélo have unveiled their first gravel-specific bike, and perhaps unsurprisingly given their history they've chosen to focus on speed.Read more