By Jim Langley

We’re always looking for new and interesting Question of the Week ideas, and you’ve provided some great ones, thanks very much. Recently, we got an idea from a reader named Michael that we weren’t sure would make a good QOTW or not.

Mike suggested the question “Do you own a 650B bike?” He stated that “many steel road, rando and touring bikes are 650B these days.”

This caught us by surprise because neither publisher John Marsh nor I thought that enough RBR readers would own bikes with 650B wheels – or even necessarily know what a 650B wheel is – to have an interest in the question.

But (and this is what we hope sets us apart a little bit), both John and I thought it was an interesting technical topic, because the 650B wheel size goes back to at least the 1940s (mostly popular in Europe) and is finally becoming more common. So, we agreed that it's worth taking a look at and sharing the info with RBR readers.

700C Compared to 650B

First, know that 650B wheels and tires can alternatively be labeled by the new 27.5-inch designation. You’ll see this more on mountain bikes. Just keep in mind that it’s the same size.

By far, most road bicycles today are still equipped with 700C wheels, which fall under the nominal rim diameter measurement of 622mm. 650B wheels are smaller, at 584mm.

That's a big difference in the size of the rims. And it means that if you have the sidepull brakes found on most 700C road bikes, it's unlikely you'll be able to simply switch from 700C to 650B wheels. The reason is that most of these brakes don't have enough brake pad adjustment to lower the pads to hit the smaller rim size.

However, things get interesting when you put tires on the two wheel sizes – because the two diameters with tires mounted are often so close (depending on the tires you’re using) that you could switch out the wheels if you have a disc-brake equipped 700C road bike with enough clearance (keep reading).

Tip: Here’s a good article about converting to 650B wheels http://www.sheldonbrown.com/650b.html

Why do people choose 650B?

The thing that made 650B wheels and tires popular was the super comfortable ride of the 650B tires, which used to run a lot wider than commonly available 700C sizes. All things being equal, wider tires are more puncture-resistant, too, making them ideal for rougher roads and even trails (an early one-off mountain bike featured 650B wheels).

In Europe where 650Bs were well known, they were the randonneuring/touring tire, versus 700C, which was considered the performance/racing size. So there didn’t need to be wider 700C tires or narrower 650Bs. That’s a simplification, but essentially each had its own niche.

This is changing today, in part because of the mountain bike phenomenon, where new wheel and tire sizes and designs have run amok. But we roadies are the beneficiaries. For example, Compass Cycles’ selection of 650Bs now runs from 32 to 48mm wide, while their 700Cs run 26 to 44mm wide.

Keep in mind that Compass also deserves credit for helping us all enjoy riding more by proving that wider tires (and lower inflation pressures) can be just as (or more) fast and efficient as skinny ones under higher pressures. And by sharing their research in their Bicycle Quarterly magazine and here in RBR (click to read: The Tire Pressure Revolution).

Clearance issues

While riding on wider tires can be game-changing, don’t spend a lot on a wheel/tire-size conversion until you’ve checked the tire clearance on your frame and fork. Not all bikes – and, especially, not all forks – can handle fatter tires.

It’s difficult to measure clearance accurately, and tire width measurements in catalogs and printed on tires aren’t always accurate. Plus, different pressures can change the tire width and even height. So, the only accurate way to check clearances to ensure tires will fit is to test fit the inflated tire/wheel combination you’re considering on your bike. And be sure to try it on both the front and rear wheel.

Tip: If you’re lucky enough to ride with friends using the wheels/tires you’re thinking of getting, you could simply ask to borrow their wheels and see if they fit in your frame.

Tip 2: If you have a 700C wheel bike with sufficient clearance, you might opt to upgrade to the widest 700C tires that fit. That’ll be much less expensive than the cost of a new wheelset and tires.

Bikes with 650B wheels

If you want to give 650Bs a try and can’t upgrade the wheels on your bike, you’ve got the perfect reason to ask Santa for a new bike this year.

As Michael pointed out, these bikes are usually found in the steel, randonneuring and touring categories. I would say to look under the gravel and maybe even the cyclocross category, too.

To point you to a few examples, check out Open Cycle's UP (for Unbeaten Path). It was one of the highlights of the 2015 Interbike show. Another interesting 650B bike is Cannondale’s Slate. Or, maybe you’d like to build a bike from a frameset using the affordable Soma Grand Randonneur or the highly regarded Lyonsport L'avecaise.


Jim Langley is RBR's Technical Editor. He has been a pro mechanic and cycling writer for more than 40 years. He's the author of Your Home Bicycle Workshop in the RBR eBookstore. Check out his "cycling aficionado" website at http://www.jimlangley.net, his Q&A blog and updates at Twitter. Jim's streak of consecutive cycling days has reached more than 8,000. Click to read Jim's full bio.

Related Topics Tech Wheels Size Sizing 700C 650B

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