Choosing 650b Vs 700c for gravel and adventure bikes
What’s the best tyre and wheel combo for your dirt rig?
Words and photos - James Raison
I remember when the Cannondale Slate knocked our collective, UCI-compliantly tall, socks off with the original Slate rocking 650b and 42mm tyres. It was one of the first times we roadies got exposed to smaller wheels and chonky (sic) tyres giving you similar diameter as the road wheels we’re all used to. Fast forward to present day and the burgeoning gravel/adventure scene is loaded with wheel and tyre options, and riders are looking for upgrades to their rigs.
So, what are the strengths and weaknesses of 650b and 700c setups from a rider’s perspective? We thought it was time to extend our series of sensible advice articles (to date including such guides as Putting together an adventure bike and the Bike buying advice) to the wheel and tyre choices faced today.
Before we dive in, a quick refresher on terminology to avoid confusion. 700c and 29” are the same. 29” wheels aren’t even 29 inches because… reasons? 650b and 27.5” are both the same too but are named differently according to MTB or road context. I don’t blame you for not knowing this, the bike industry can be silly and confusing. Onward!
The Continental Terra Speed is one of our favourite gravel tyres, just don’t expect a long life out of them!
GEOMETRY
A crucial consideration is what the wheel and tyre choice does to your bike’s geometry and handling.
It’s all about trail which is the measurement when you crunch head angle, fork offset, and the total diameter of your tyre when it’s on the rim. The trail value is the main determinant of how a bike steers, and your tyre choice changes it substantially. Bigger tyres means a bigger tyre diameter and slower steering. The opposite is true of smaller tyres where you’ll get sharper or twitchier steering.
Most bike geometries are optimised around a specific range of wheel/tyre sizes. With adventure and gravel bikes comes a wide range of wheel and tyre sizes and thus broad range of handling characteristics.
There’s a handy calculator that give you a total circumference based on entering a wheel and tyre dimensions. The minor inconvenience for gravel and off-road tyres is the tread does add to circumference. So use the calculator as a guide only and not the arbiter of truth.
Another crucial consideration is your BB height. Dropping wheel and tyre diameter could see your BB get a little close to the ground and cause pedal strikes. I started whacking things more often with 650b.
WEIGHT
Great news! 650b wheels are lighter than their equivalent 700c. So you should buy them immediately if not sooner, right? Well, calm-yer-farm there captain weight weenie because there’s a catch; 650b tyres are hefty.
35mm is a good width for tyres but they come with limitations
My Grove came with AlexRims Boondocks 3s with a respectable 1,750g of claimed weight. The fancy carbon-rimmed Hunt Adventure Carbon V2s are an ethereal 1,425g claimed. Guess how much difference the Hunts made to the total weight of the Grove once setup with tyres, sealant, and cassette. None. The bike weighs the same with both setups.. That extra money and fancy carbon buys you almost no weight benefits once you’ve added on hundreds of extra rubber grams. To be exact, each GravelKing 650x48 tyre is 160g more than the 700x35.
Now, I’m not saying weight should instruct your decision of wheel and tyre choices. We’re all cyclists though and the impulse to count grams is strong. It’s worth noting that dollar-for-grams of wheel weight 700c is the way to go.
Light wheels + heavy tyres mean you’ll break even on your investment with smaller wheels when you put them on the scales
THE RIDE
Ride properties are a tough thing to cover we’re talking about every tyre size from 650bx42 mm to 29x2.1”. So I’ll set some boundaries on this and keep it between 650x48 and 700x45. When choosing your wheel and tyre combo then you’ll be weighing up expected tyre pressure, desired grip/rolling resistance balance, and confidence on tough terrain.
I love running low tyre pressures. I’m not far off door knocking to hand out flyers about the benefits of low psi; Hello, have you got a moment to talk about our Lord and Saviour Jan Heine? I ran the 650b wheels as low as 20 psi with the Panaracer GravelKing SKs. The initial squishiness seems weird on the tarmac but it’s plush and lovely on shifty surfaces. It improves the ride quality, protects you better from bumps and whacks, and gives you a bigger contact patch with which you can send it. The small diameter wheel/tyre combo keeps the handling lively and sharp. A genuinely fun combo.
48mm of rubber gives a big contact patch
The same tyres in 700c x 35mm feel quick on compacted gravel roads, but are bumpier owing to the higher tyre pressure, have a smaller contact patch, and give less confidence on single track. There’s simply less rubber, and less air between you and the ground.
When you expand the rubber over 40mm, a 700c tyre can have even more sendability but with slowed steering. Cramming 45-50mm tyres gives you similar contact patch as a 650x48mm but with the added diameter giving greater bump resistance. Now, most gravel bikes are topping out arount 43 mm clearance, and actually shipping with tyres 35-40mm. That width is perfect for your garden variety gravel riding.
TYRE AND TUBE CHOICES
There’s inconveniences of running 650b until it reaches a certain market share.
Tubes are harder to find and your ride companions who ride with 700c wheels are of no help if you get a puncture. It’s something to keep in mind when you’re going adventuring because you’re solely responsible for your own spares.
All hail the yoked chainstay! The unsung hero of gravel biking
2019 finds an embarrassment of riches with 700c tyres for churning the dirt. 650b is not so spoilt for choice. I’ve been planning out some tyres I’d like to test over the coming months and many of them don’t come with a 650b version, which is a bummer. There’s still some great options like the Panaracer GravelKing SK and the legendary Schwalbe G-One. If you want the world of tyre choices available then 700c is the way to go. For balance, WTB are pumping out some very classy 650b only options.
Don’t panic though, there’s a lot of 27.5x2.1”/2.2” speed-focused XC MTB tyres that would be a riot on gravel. Think Schwalbe Thunder Burt, Maxxis Ikon, and Vittoria Peyote as examples.
SO WHAT DO YOU NEED?
I guess the decision can be made simple: if you’re riding gravel roads that aren’t too gnarly then 700c wheels and tyres 35-43 mm have you covered. They’re the best balance of weight, grip, and rolling resistance plus the added benefits of generous tyre availability. Those wanting to hit the single tracks, seek out some rock gardens, or put a lot of cushion between themselves and the ground should consider the 650bx48 to 2.1” range.
THE RECOMMENDATIONS
Ok, enough balanced talk. Time for some action! So, what should you actually equip yourself with? Do you identify with any of these categories:
Mixed tarmac and gravel is my jam: Easy, 700c wheels with 35-40mm tyres will have you covered. Check out Panaracer GravelKing SKs (review), Contental Terra Speed (review), Schwalbe G-One Allrounds, Donnelly X’Plor MSOs (review), Vittoria Terreno Dry, and Bontrager GR1s for great all-rounders.
I want to be comfortable on a bit of everything: Awesome, you can look at 650b and 700c. In 650b you can go with with 48mm tyres like the Panaracer GravelKing SKs (review), Maxxis Ramblers, or WTB Ventures. Those with a tast for the finer things can try the Rene Herse Juniper Ridge. For 700c go something in the 43-45mm range like WTB Riddlers, Panaracer GravelKing SKs (review), or Kenda Flintridge.
Enough talk, I just want to send it: 27.5x2.1”-ish tyres will see you happily shredding the gnar while your collarbones quake in fright. Check out the Maxxis Ikons (which comes in tasty tanwall), the Schwalbe Thunder Burt, WTB Nano, or Vittoria Mezcal.
I want to adventure with no worries: Find the bike with the biggest tyre clearance you can, and fill it with the biggest tyres it’ll allow. Simple!
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