In the bike industry, it sometimes seems like we have new standards coming out of our ears, be they bottom bracket standards, headset sizes or handlebar clamp sizes (but at least these days we ‘only’ typically use four different seat post diameter standards!).
It may also seem like this is the case for wheel size standards, but in actual fact, many of the modern wheel sizes we see today have been around for quite some time already. 700c has been around since the 19th century, and the 29er mountain bike wheel is essentially the same standard as 700c. The now less popular 26inch wheel has also been around for over one hundred years, but became popular in the 1930s with American cruiser style bikes. But what about 650b? Isn’t this a new standard that was conjured up for use on modern gravel and all-road type bikes? The answer is no. 650b, or 27.5 inch as it’s known as in the mountain bike world, is indeed probably one of the youngest wheel standards in use today, but nonetheless it has been rolling about since the golden age of French randonneuring in the 1930s. The potential for 650b’s off-road use was spotted early on – in the 1950s, members of the British Rough Stuff Fellowship would fit 650b wheels into frames made for larger diameter wheels. This facilitated the use of larger volume tyres. The similar overall diameter of a 650b wheel with a higher volume tyre, and a 700c road rim with a standard road tyre width means that there is a minimal difference in ride handling between the two. We can choose a wheel/tyre combo to suit the type of surface we want to ride. Today, we see frameset designs that allow for the interchanging of wheelsets for the same reasons that the cyclists of the Rough Stuff Fellowship adopted 650b. Take the Bombtrack Hook EXT for example; the frame allows max wheel/tyre combos of 700c x 40c and 650b x 52c, meaning that it can easily be converted to and from road and gravel bike.
Given that we can achieve very similar wheel circumferences using certain rim/tyre combinations, why indeed would we choose a 700c wheel over a 650b at all? The ride could be more comfortable with a thicker 650b tyre versus a slimmer 700c, and there are many 650b tyres available on the market with slick carcasses, just like conventional road tyres. If we can buy high end 650b tyres with supple casings that roll very quickly, then why still choose a 700c wheelset?
There are, however, a few reasons why we might opt to equip our bike with 700c. Tests have shown that the smaller frontal area of a narrower tyre presents less aerodynamic drag. There is also the argument that a 700c wheel maintains better momentum than a 650b wheel. However, if we are trying to stick with two wheelsets of the same diameter, then theoretically, a 650b wheel with a 47mm tyre compared to a 700c wheel with a 28mm tyre (both having approximately 2130mm of circumference) will roll in a very similar way, the 650b setup possibly even outperforming 700c x 28c in the real world. If we wanted to reap the benefits of a larger diameter 700c wheel, then we would have to fit a larger volume tyre and potentially push the tyre clearance on the frame to its limit.
With the right frame, choosing 650b over 700c means that we can achieve the smooth ride that comes with a larger volume tyre, but maintain the responsive handling of a road bike. Provided there is enough lateral clearance, we could fit out a more aggressive frameset with set of 650b wheels and high volume tyres. In the Bombtrack line-up we have to look no further than the Audax range. The short chainstays and steeper, more road orientated head and seat tube angles make for a sporty ride that emulates that of a thoroughbred road bike. But its 650b x 47c tyres make for great comfort on all surfaces. As mentioned earlier, the circumference of the 650b x 47c setup also matches that of a 700c x 28c wheel, therefore amplifying the sporty road bike ride characteristics of the frame.
If we were to compare the ride characteristics of a 650b wheelset directly next to a 700c wheelset, both fitted with tyres of the same width, we would notice an obvious difference. The smaller diameter 650b setup would feel more nimble and snappier to accelerate, whereas the 700c would not be quite as quick to accelerate, but the greater momentum that the larger diameter wheel carries would mean that maintaining speed over longer distances would feel more natural. A larger diameter wheel will also roll over obstacles and rougher surfaces with more ease – the larger the wheel, the smaller the obstacle by comparison. This basic principal is not a new discovery by any means. In the days before the safety bicycle and the pneumatic tyre, the huge front wheel of the penny-farthing meant that rolling over rudimentary road surfaces was made more forgiving, at the same time meaning that the rider’s pedaling cadence could be kept lower at higher speeds.
But what do we have to choose from when we want new tyres? Another factor to consider is the availability of stock on the market. Where there are indeed some truly great performing 650b tyres available with brands today, the fact of the matter is that there are many more examples of 700c tyres out there to choose from. 700c is simply a more popular choice in the modern cycling world – something that is driven by what the pros use on their bikes, and the simplification of off-the-peg bike specification.
Choosing a wheelset size doesn’t always have to be dictated by the type of surfaces we want to ride. Bikes come in a huge range of sizes reflecting the diversity in height of the people who ride them. Sometimes, designing a bike that will fit a shorter cyclist properly can be a challenge. Designing a frameset that has a short enough reach without encountering problems with toe overlap can be made much easier when working around a smaller diameter wheel. And as pointed out earlier, 650b offers a ride quality that when used with the right frame geometry, can closely mimic the behaviour of a 700c wheel in terms of handling. Naturally, this can have a positive effect on parameters such as a frame’s stand-over height too, and can really help to keep things more proportionally dialed-in. This school of thought can also be applied to designing frames for much taller riders, where larger wheels may be more suitable to maintain proper proportions. 700c is generally a suitable choice for larger frame sizes, but occasionally we see custom framebuilders building frames to accommodate even larger wheels, 32inch and 36inch rim sizes being employed.
So what will you look out for next time you’re inspecting a bike’s spec? Will you be curious to see what size wheels will fit and what difference to your riding experience they will make? Or are you dead set on a wheel size and know exactly what size works for you? Perhaps this quick dive into the 650b world will galvanise what you already know, or maybe it will fuel your curiosity to explore it for yourself. Maybe this has whet your appetite and kicked you down the rabbit hole! If this is the case, fear not. Keep an eye out for the next chapter in the story of 650b vs 700c, we’re not out of the woods yet!
SEIDO Components
July 2025
By Peter Skelton