What do 650B & 700C actually mean?
For the vast majority of road cyclists, there has only ever been one size of wheel to consider – referred to as 700C. Certainly since the mid-1980’s, road bike designers have come to consider this as the “standard” wheel size. However, you only have to look across to the world of mountain biking to see that this “one size fits all” approach doesn’t always lead to the best ride characteristics.
Before we delve into the detail, time for a quick history lesson. From the earliest production bicycles, through to the early 1900’s it wouldn’t be uncommon for each individual manufacturer to specify their own bespoke wheel size for their frames. It was the introduction of the pneumatic tyre (by Dunlop) that first drove the need for standardised sizing – wheel manufacturers wanted their riders to be able to fit a tyre from a third party, and the two parts had to fit together. In order to ensure a safe fit, tyres and rims were designed to the same Bead Seat Diameter or inner diameter of the tyre.
Completely counterintuitively, tyres were still labelled by their outer diameter, rather than BSD. The French sizing system was laid out with the nominal outside diameter (in the case of road wheels, 700mm), followed by a letter to denote tyre width (C). Over time, the number of standards used by manufacturers decreased, eventually leaving only 700C as the road “standard”.
Another common size under the French system was a 650 size tyre (650mm outer diameter), which was most popular in a B width, hence 650B.
But what does this mean for me? Put simply, a 650B wheel has a smaller Bead Seat Diameter than a 700C wheel. The 650B has a BSD of 584mm vs. 622mm for the 700C, so the wheel itself is 38mm smaller in diameter.
So what does this mean when choosing a wheel?
At first look, a 700C wheel fitted with a 28mm tyre will have the same total diameter (678mm) as a 650B wheel running a 47mm tyre. But, critically, the wider tyre on the 650B will have a much higher air volume (approximately 2.5 to 3 times as much), massively changing how the wheel will ride. A larger tyre will allow you to run far lower pressures, increasing ride comfort and grip. The tyre will be more able to deform around rough surfaces, providing a smoother and more assured ride.
On the other hand, if you compare the two wheels fitted with identically-sized tyres, the total diameter of the 650B setup will be smaller. This too will also have an impact on the ride, as the smaller wheel reduces the fork trail and wheelbase. Shorter geometry like this makes for more responsive handling.
Another impact to be considered is on gearing – the smaller 650B wheel will make gearing ever so slightly easier as the bike will travel a shorter distance for each wheel rotation.
It’s also sometimes claimed that the larger 700C wheel will “roll over” larger bumps and obstacles more easily. You certainly see this cited as a consideration in mountain biking when choosing between say a 26er and a 29er, however with a 650B vs. 700C choice it’s a bit more nuanced as you’ll see below.
Finally, due to its smaller size, the 650B wheel will likely be lighter than its 700C counterpart. Assuming of course there aren’t any differences in rim design (other than size). Don’t forget that a wider tyre will almost definitely offset any weight saving (and more) though! The smaller wheel will require shorter spokes as well, actually increasing the overall strength of the wheel.
So is it the wheel or the tyre?
As much as the differences in ride performance can be attributed to changing your choice of wheel size, all of this depends on the size of tyre that you fit to the wheel. With the growth in popularity of disc brakes we are seeing more and more frames that can be run with either a 650B or 700C wheel. Shrinking the wheel leaves more space for the tyre, allowing riders to adjust the performance to the terrain they’re riding on. So whilst it might be counterintuitive to say so as a wheel brand, pretty much all of the differences you’ll see between the two wheel sizes can be attributed to tyre choice. Arguably the main reason to choose one wheel size over the other is to allow you to run the tyre size that you prefer, whilst also maintaining handling characteristics suitable for your riding.
Should I run a 650B wheel or a 700C wheel?
- Rougher off-road riding, taking in gravel trails, light singletrack and with a majority of unpaved surfaces
- Looser surfaces where grip is a priority
- Snappy, sharp handling
For lighter off-road riding, including rides which will also include paved roads or tarmac, a 700C wheel will come closer to providing a “best of both worlds” type ride, combining road performance with off-road versatility.
Beyond that, it really does come down to personal preference. Whether you to choose to run a 650B wheel with a 47mm tyre, or a 700C wheel with a 38mm tyre, Parcours has a wheel for you. In either case, we’re sure that you’ll find yourself riding further than before, really opening up your ride horizons!
One final note to help avoid confusion – a 650B wheel is not the same as a 650C wheel that used to be used on some smaller road frames. Thanks to the French sizing system, the Bead Seat Diameter is different, so the two aren’t interchangeable!