With fatter tyres on smaller wheels, the 650B standard gives the same rolling size as regular 700C wheels with more cushion and grip. Should you consider a bike with this reborn wheel spec?
What is 650B?
This is a wheel size with smaller rims than the 700C road bike standard, but larger than the 26-inch size that was the standard for mountain bikes until a few years ago. Because the rims are smaller, fitting 650B wheels into road and gravel bikes that usually take 700C wheels allows the use of fatter tyres with little or no alteration to the frame design, assuming you have disc brakes.
There used to be loads of French wheel sizes, designated by the rolling diameter of the tyre in millimetres, and a letter. The road bike standard 700C is one of these sizes; it originally had quite fat tyres that bulked things out to a rolling diameter of 700mm.
Wheel size designations are a proper omnishambles. The only way to be sure a tyre will fit a particular rim is to look at the size of the bead seat, the part of the rim where the tyre fits when inflated. Your 700C wheels have a bead seat diameter of 622mm; for 650B it's 584mm.
The 650B size was popular with French touring cyclists back in the 60s, and has been brought back from the brink of extinction by the mountain bike industry. It has pretty much replaced the original mountain bike 26-inch wheels, which have a bead seat diameter of 559mm. Also referred to as 27.5in, the wheel size is now found on bikes from entry-level hardtails to downhill bikes.
But 650B is no longer just on mountain bikes. Road bike manufacturers from small independent frame builders like Hallett Handbuilt Cycles to mainstream brands like Cannondale have adopted it for all-purpose and gravel bikes.
The combination of a 650B wheel's 584mm rim and a tyre width of between 30 and 50mm gives about the same overall wheel size as a regular 700C rim and 25mm tyre, so the rolling speed and handling characteristics will be similar to a regular road bike.
Benefits include additional cushioning from the bigger volume of air, providing a smoother ride, and a larger contact patch which boosts traction, ideal for mixed terrain and slippery roads.
Do we need a new wheel size?
There has been a move to wider tyres on endurance and sportives bikes over the past few years, with bikes like the Cannondale Synapse and Giant Defy, which both cater for up to 28mm tyres, proving incredibly popular with cyclists that want a bit of extra comfort.
Even professional road race cyclists, once wedded to skinny 22 and 23mm tyres, are now switching to 25mm and 26mm tyres as standard. But it's arguably cyclists seeking comfort, especially with road conditions deteriorating due to lack of maintenance, that have been pushing manufacturers to develop bikes with space for wider tyres.
The adoption of wider tyres has been swift. With many cyclists cottoning onto the benefits of wider tyres, many are seeking bikes capable of taking even wider tyres. A mere 28mm just doesn't cut it anymore. The latest crop of gravel and adventure bikes massively increase clearance over the endurance bikes, accepting tyre widths between 30 and 50mm.
One significant benefit of 650B is to do with geometry. A 42mm tyre on a 650B rim provides about the same outside diameter as a 23mm tyre on a 700C wheel, so you can fit much wider tyres to the bike without requiring any drastic changes to the geometry of the frame and fork.
A bigger tyre on a 700C rim requires changes to the frame and geometry. The chainstays need to be longer, and with it the wheelbase and the fork needs to be taller. This can impact the handling of the bike and takes it further away from the responsiveness and agility that is the hallmark of a road bike.
Wider tyres are becoming more and more popular. Gravel and adventure bikes offer a new option for the growing number of cyclists that want a versatile bike to cover different road surfaces and terrain (and previously might have chosen a cyclocross bike) and with 650B is back in fashion in the mountain bike world. All of that has made bike makers look again at a wheel size alternative.
With the mountain bike industry geared up to developing 650B bikes, there’s now a lot bigger choice of wheels. There’s also a cross-pollination of ideas and engineering, especially with the growing gravel and adventure bike sector, which owes a lot to the mountain bike world. It was really only a matter of time.
How Cannondale went 650B with the Slate
When it launched the Slate a couple of years ago, Cannondale reckoned that a 650B rim with a 42mm tyre was the perfect pairing for a bike designed to be fast and agile on the road, like a regular road bike, but capable when the surface turns to dirt and gravel.
“On Slate, the decision to go for 650B was natural for us,” Cannondale's David Devine says. “We knew which tyre size we wanted, 42mm. We knew which chainstay length we wanted, 405mm. When we discovered the rollout of 700x22mm and 650x42mm were roughly the same, we decided it was the best wheel size for achieving our desired tyre volume within the set geometry. Traditional 700C wheels, paired with the 42mm tyre would have driven a longer chainstay length, and would have necessitated a higher frame stack while maintaining the same 30mm Lefty Oliver Suspension fork.
“650B wheels offer our desired geometry and tyre volume together in one package, rather than having to make a compromise with smaller tyres or longer chainstays,” explains Devine.
The bespoke option
It’s not just the big players in the cycling industry that are paying attention to the benefits of 650B. Bespoke frame builders have been closer to the cutting-edge of bicycle design than many of the bigger corporations for some time, with a closer relationship to their customers and able to produce one-off frames much more quickly.
Richard Hallett of Hallett Handbuilt Cycles has been dabbling with the 650B wheel size and appears convinced of the benefits, saying that ride comfort and grip are the big advantages.
“650B road tyres such as the Grand Bois Cypres and Hetre offer demonstrable improvements over 700C tyres up to 28c in rolling resistance, ride comfort, grip, all-roads riding and, importantly, safety,” says Hallett, “so using 650B wheel and tyres I can build a touring, audax, utility or training bike that offers superior performance in these respects.
“There is a weight penalty, the amount depending on tyre size, which is why they aren't used in racing. If someone wants a racing or sportive bike, I recommend 700C, up to 25mm.”
Road.cc took a closer look at one of Richard Hallett’s bespoke bikes last year, a steel frame and fork with 650B wheels and 42mm tyres. His aim was to build a fast, comfortable and fine-handling bike and put it through its paces in the 300km Dragon Ride sportive, a stern test indeed for any road bike.
We’ve been here before haven’t we?
Sort of, yes. Using smaller mountain bike wheels on a road bike is nothing new of course. There have been many road bikes designed with 26-inch mountain bike wheels that allow clearance for larger tyres: the Surly Long Haul Trucker is one such bike that can, as well as regular 700C wheels, take a 26in rim with a tyre width up to 62mm.
While such bikes have been a quirky oddity to most regular road cyclists, the growing popularity of wider tyres on all road bikes and a shift towards comfort over outright speed, could mean we'll be seeing a lot more new bikes that take a fresh look at the advantage of combining a smaller wheel with a bigger tyres.
Was Cannondale’s Slate the start of a new trend or simply a one-off? David Devine thought at the time that we were likely to see more manufacturers take an interest.
“I do anticipate that other bike companies will trend toward making 650B road bikes,” said Devine. “Already, we have some tyre manufacturers approaching us to make sure they are opening moulds that will be compatible with Slate. In addition to the tyres available from Panaracer, you will see tyres from some of the main brands already coming to the market in this size. The Slate will help broaden the tyre selection for 650B x 42mm tubeless, all-road tyres. It’s something that has been around in the hand built community for some time.”
While there are clearly some very good reasons for going to a 650B wheel sizes, there are some downsides. A 42mm tyre is heavy, about 400g, about twice the weight of a regular narrow road tyre, and that can extra weight at the outside of the wheel could impact acceleration and speed. Those concerns might be easily outweighed by the comfort, durability and robustness for tackling rough roads and gravel paths and off-road tracks, though. 650B could make sense to a lot of cyclists.
Perhaps the mainstream bike brands won’t have it all to themselves, argued Richard Hallett.
“The large-scale manufacturers seem to have put all their eggs in the 700C wheel basket so we see everything from race and sportive bikes on 700Cx23/25 to gravel and adventure bikes with 700Cx32/35 tyres,” he said. “These are inevitably heavier than 650Bx32 with no appreciable performance advantage, but investment in 650B would cost money, so I suspect 650B road bikes will remain a small part of the market for the moment.”
The latest 650B bikes
Three years later, it looks like Hallett was more or less right, but a few more manufacturers have taken the plunge and added a 650B-shod bike to their ranges. Canadian brands Kona and Norco both have gravel bikes with 650B wheels, as do the UK's Genesis, Chain Reaction Cycles house brand Vitus and boutique marque Mason Cycles.
And after being very hard to find, the Slate was back in the UK for 2019 with two models, both with SRAM 1 X 11 transmissions and the Lefty 30mm suspension fork. Cannondale still describes the Slate as "a full-tilt road bike with legit off-road chops" a rather confusing line, but at least the 2019 models come with knobbly tyres. We haven't been able to find a stockist of the 2020 Slates, though Cannondale does still list them.
One of the early adopters of the whole gravel/adventure/do-it-all bikes, the Cotic Escapade has had a few upgrades since its inception a good five or six years ago. Larger tyre clearances, a new carbon fork and a tapered head tube have now upped the performance and dropped the weight, making the new model an absolute joy to ride whether on or off road.
The WI.DE (Winding Detours) gravel bike from Open takes wider tyres than the company’s original UP from 2015 and is all the better for it, with supreme speed over all sorts of surfaces, infused with great handling and low weight.
Gravel bikes have been edging closer to the territory occupied by mountain bikes for a few years now, leading to many accusations they are nothing but glorified rigid mountain bikes with curly bars. The WI.DE suggests there's some truth in these accusations; it has space for up to 60mm (2.3in) tyres on 650b rims, as wide as many cross-country mountain bikes.
Our David Arthur rode the WI.DE with 57mm tyres and reports that it was nimble at low speed when swerving around trees on singletrack, while stable at higher speeds on loose gravel tracks. The steering is calm at high speeds making it a relaxing bike to ride on long distances because it’s not twitchy.
If you think the big tyres will mean a sluggish ride, think again. The WI.DE is stupendously quick over all terrain, whether it’s a road where it manages to not give out much speed to a pure road bike, or along rough gravel roads or forest tracks. The speed of the Open was its defining feature. The high stiffness of the frame delivers a sprightly uptake of speed and the low weight - 8.75kg for the pictured size medium test bike - ensures there’s no hill too steep or tough for the WI.DE to conquer.
The name is 'gravel' backwards, but there's actually nothing backwards about Saracen's 650B-shod gravel bikes. The Levargs are fast and fun bikes, well-suited to taming the UK’s poorly surfaced roads and bashing along dirt and gravel tracks.
The Genesis Fugio, above, is solidly a gravel bike, with 50mm tyres. It’s almost a mountain bike with drop bars, and fits the growing trend for big tyred drop bar road bikes that can go almost anywhere. The frame is made from chromoly double butted tubing, with a full carbon fibre fork.
There are two models, Fugio 20 and Fugio 30. Both have 1 X 11 transmissions with 11-42 cassettes. The Fugio 20 in Genesis' Mjolnir chromoly has SRAM Apex components, cable-actuated disc brakes and WTB Venture TCS tyres, with a 42-tooth chainring.
The more expensive Fugio 30 is made from Reynolds 725 heat-treated tubing, which sheds a bit of weight. The Fugio 30 is hung with Shimano's new GRX 810 groupset and drops the gearing slightly with a 40-tooth chainring.
A Fugio frameset is £719.99 if you want to start from scratch and build your own.
Four models of Kona's venerable Rove adventure/touring bike come with 650B wheels, though the frame will also accommodate 700C wheels. There are two aluminium-framed bikes, including the Rove NRB DL, above, and two with steel frames, including the special edition Swift Rove which comes with a set of touring bags.
Can't live without composites? Kona's Libre carbon gravel bike has switched to 650B for 2020.
This update of the gravel/adventure bike Vitus launched in 2018, the latest Substance has a carbon fibre frame and fork and SRAM Rival 1X11 gearing.
The Ibis Hakka MX is a descendant of the US company’s previous Hakkalugi cyclocross bike but geared much more towards the gravel and adventure riding, rather than racing in the mud. Like most of the bikes here it will take 650B or 700C wheels, though you get the fattest tyre option with 650B: the stock Schwalbe Thunder Burt tyres are 54mm wide. It's a long way from cheap even in the base SRAM Rival 1X spec above, but you're getting a frame from one of the best-regarded carbon shops in the business.
From the detail-obsessed mind of Dom Mason comes a highly capable adventure bike with a feature-packed aluminium frame, splendid aesthetics, and handling that ensures it's as at home on the road as it is on the trail.
Cannondale offers two models of Slate, with SRAM Apex and SRAM Force at the lower and higher price points respectively, but the more expensive Slate is now practically impossible to find. The cheaper version is getting scarce too - the link above takes you to a size M while there are a few XLs around for £1,999. Aside from the difference in groupset quality, the specs are very similar. Both have 44-tooth single chainrings with 11-42 cassettes and knobby WTB Resolute tyres.
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David has worked on the road.cc tech team since July 2012. Previously he was editor of Bikemagic.com and before that staff writer at RCUK. He's a seasoned cyclist of all disciplines, from road to mountain biking, touring to cyclo-cross, he only wishes he had time to ride them all. He's mildly competitive, though he'll never admit it, and is a frequent road racer but is too lazy to do really well. He currently resides in the Cotswolds.