[This article was originally published November 25, 2015 and updated December 11, 2017]
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 impacts the handling of the bike and takes it further away from the responsiveness and agility that is the hallmark of a road bikes
Wider tyres are becoming more and more popular. Ggravel 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, 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 x42mm 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
Two 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 for 2018. Canadian brands Kona and Norco both have gravel bikes in their ranges with 650B wheels, as do the UK's Genesis, Chain Reaction Cycles house brand Vitus and boutique marque Mason Cycles.
It's not quite clear what's going on at Cannondale, though. The US range has shrunk to just two models, both with the Lefty suspension fork and Cannondale UK isn't bringing either of them across the pond. The original Slate was unarguably very clever, but It was never quite clear what it was for. Cannondale didn't help by describing it as "a full-tilt road bike with legit off-road chops" (a line they're still using) or fitting it with slick tyres. The two 2018 models have knobblies, and maybe the Slate will return to the UK when Cannondale decides exactly how and where we're supposed to ride it.
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 Mjölnir chromoly double butted tubing, with a full carbon fibre fork.
A Fugio frameset is £799.99 and there's a complete bike as pictured for £1,999.99 with a Shimano 105 groupset and RS-505 hydro brakes.
Norco Search XR — £TBA
Norco's new Search XR is a 650B version of the Search bike that Norco has been offering for a few years. There are five models, three with carbon fibre frames and two with frames in Reynolds 725 heat-treated chromoly steel, an unusual move that will no doubt endear the Search XR to UK steel frame fans. There's no word as yet on UK prices and availability.
The latest incarnation of Kona's venerable Rove adventure/touring bike comes with 650B wheels, though the frame will also accommodate 700C wheels. There are two aluminium-framed bikes, including the Rove NRB, above, and one with a Reynolds 853 steel frame.
A new model for 2018, the Substance V2 has a chromoly steel frame and carbon fibre fork and comes in two versions, with Shimano 105 components, above, or with SRAM Apex 1X. Both have hydraulic disc brakes, so the only major difference is whether you want the simplicity of one chainring or the versatility of two.
The Ibis Hakka MK 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.
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.