Particularly for off-road disciplines, you’re often offered a choice in wheel size when buying or building a bike.
The wheelset of a bicycle includes the hubs, bearings, spokes, rims, and often the tubes and tires themselves. It’s not uncommon to be presented with a choice of wheel size, specifically if you’re buying a gravel or mountain bike.
Two of the most common sizes you’ll come across are 650b and 700c.
These two different sizes can offer a remarkably different experience when riding, and each comes with its own pros and cons.
But what are the advantages and disadvantages of 650b vs 700c wheels? Which should you choose?
To get you up to speed, we’ll be covering:
- What Are 650b And 700c Wheels?
- Why Choose 650b Wheels?
- Why Choose 700c Wheels?
Ready for a showdown: 650b vs 700c?
What Are 650b and 700c wheels?
The wheels of a bike can have a massive bearing on how the bike feels to ride.
The smoothness of the bearings themselves, the material the wheels are made out of, and the tread pattern of the tires all have a huge effect on your ride.
But above all of this, the size of the wheels will likely make the biggest difference to your experience.
Decoding Different Wheel Sizes
The naming of the different wheel sizes, frustratingly, is extremely confusing.
First of all, there’s the standard size you might find on a road bike. These are 700c wheels, which refers to the fact that the full wheel – including the tire – has a diameter of 700 mm.
When a wheel is measured in this way, including the tire (and in mm), it’s called French Sizing.
If you’re a mountain biker, you will have heard this exact same size quoted in a different way.
A 29-inch wheel – or 29er – is the same as a 700c wheel (even though 29 inches is actually 736 mm). The diameter is measured to be (just under) 29 inches from the outside of the tire, just like French sizing.
Lastly, there’s another way to describe such wheels, referred to as ISO sizing.
This measures from the outside of the rim, and not the tire. So, the ISO size of a 700c, or 29-inch wheel is 622mm.
- Want to know more? Check out What Is A 700c Wheel? Everything You Need To Know!
So, a 650b wheel is the “French” name for a wheel with a diameter of 650 mm. This is the same as the 27.5-inch wheel size – and the ISO size of 584 mm.
You might – and definitely should – find this haphazard, confusing mismatch of metric and imperial systems, as well as different measuring conventions, extremely upsetting. Please don’t hold it against us.
Why Do You Even Need A choice?
Well for road bikes, you often don’t.
Road bikes have pretty much always used 700c wheels, and although there are some available with smaller ones, this is usually just a matter of being proportional to a smaller bike.
The idea of different-sized wheels came from mountain bikes.
Old-school, ’90s mountain bikes almost universally came with 26″ wheels. Mountain bikes, hailing from the US, tend to use imperial measurements for their wheels.
However, after a shift in the way mountain bikes were designed – tending to prioritze comfort a little more – we were left with very different machines with more suspension travel, wider handlebars, and most of all, bigger wheels.
This initially shifted to 27.5″, or 650b wheels. However, as time went on, the wheels grew even more, and now many modern mountain bikes are “29ers” – that is, they have 29″ wheels.
So if you’ve perused many second-hand MTB listings, you’ll likely have seen many different choices for wheel size, likely due to the release date of the bikes you’re considering.
But, this question of 700c Vs 650b has really come to the fore with the conception of cycling’s newest discipline – gravel biking.
Gravel bikes are a fantastic blend of old-school mountain bikes and road bikes, taking bits of each to form an extremely versatile machine that allows you to traverse asphalt, gravel, or even MTB trails with relative efficiency.
So, since they are a blend of their on- and off-road cousins, it begs the question: What sized wheels are best for these machines?
Unfortunately, that’s a pretty subjective question and ultimately comes down to your riding style and personal preference. Having said that, in order to make that personal decision, you have to know the advantages and disadvantages of 650b vs 700c gravel bikes.
Why Choose 650b Wheels?
650b wheels come with a number of pros and cons – many of which, bizarrely, are not directly related to the diameter of the wheel.
You’ll likely already know that when purchasing a tire, there are two sizes to consider. For sure, the diameter matters, but it’s also about the width of the tire.
Any tire will be sized in the format “diameter x width”. So, in French sizing, an example wheel size for a gravel bike might be “650b x 45 mm”
It’s important to understand that these measurements are inherently linked, for two reasons.
Firstly, your gravel bike will have a given tire clearance for each type of wheel. A 700c wheel will normally allow for a lower-width tire since the forks and stays tend to converge as you move up the bike from the ground.
Secondly, the width of the tire will increase its volume, and in turn, the total diameter of the wheel. In actuality, a 650b x 53 mm wheel and tire has the same total diameter as a 700c x 32mm wheel.
This is why ISO sizes were invented – French sizing is horrifically flawed when you consider that the total diameter of the wheel-tire system is of course affected by the width of the tire.
This leads us to the most important advantage of 650b wheels.
They allow you to fit wider tires on your bike. This allows you to run at lower tire pressure, resulting in an increased grip on the terrain and decreased chance of pinch punctures.
These benefits become even more pronounced if you run tubeless.
This will make a 650b wheel a better choice for gnarly singletrack and MTB trails than 700c, since the wheel has a greater grip on the ground, and you’re less likely to puncture on the sharp rocks and bumps of the terrain.
Another advantage of 650b wheels is that they are significantly stronger than 700c. This is because the spokes are shorter in length and so require a greater force to deform or buckle.
This is again a major benefit for those who are seeking the toughest terrain around – they have less chance of damaging their expensive wheelset.
Another advantage of 650b is that they are lighter. This is because they simply have a smaller amount of metal or carbon making up the wheel itself. A lighter wheel will allow you to accelerate and decelerate more efficiently than a heavier wheel.
There is a common thought that reducing the weight of the wheels and tires, or the “rotating weight” on the bike makes more difference than the same reduction in the frame – this is actually a myth and is debunked in this video – though it does affect the handling.
Another, perhaps minor consideration, is that a 650b wheel will make your gearing easier.
When you consider that your lowest gear ratio will force the wheel to spin a certain number of times per revolution, the distance the bike travels for each such wheel revolution is decreased with a wheel of smaller circumference, making it easier to push.
Why Choose 700c Wheels?
But if 650b wheels are so great, then why have mountain bikers shifted to larger wheels?
Well, there are also advantages to 700c wheels. The first – and perhaps most significant – is that a 700c wheel has increased rollover.
This means that it will swallow larger obstacles on the trail more easily. This might seem bizarre at first but, when you think about it, it makes perfect sense.
The larger size of the wheel grants it more circumference to make contact with the obstacle, gripping it and allowing the wheel to roll over it. So, theoretically, the larger the wheel, the larger the obstacle it can roll over.
But in practice, it’s not quite black and white. Although a 700c wheel is larger, it will generally be used with thinner tires. This means that the difference in diameter with a 650b run with fatter tires is actually going to be quite minimal.
(This isn’t often the case with mountain bike wheels, since they have fewer constraints on tire clearance, so moving up in diameter size doesn’t necessarily entail a sacrifice of tire width.)
Another thing to consider is whether or not you’re going to be riding on roads a lot. The fatter tires and smaller diameters that come with the use of 650bs generally increase rolling resistance, particularly on smoother surfaces.
So if you’re often going to be riding on roads and light gravel, then 700c wheels will likely be the best choice for you.
A more obvious benefit to 700c at a consumer level is that most gravel bikes come fitted with 700c wheels as stock, and you don’t need to go out and splurge on a new set of wheels.
The thing we thought of as a benefit in the discussion 650b wheels can also be thought of as a negative, depending on your perspective.
Although a lighter 650b wheel will accelerate and decelerate more easily, this means that it won’t maintain a constant speed as easily as a 700c wheel.
So, again, if you’re riding on roads and light gravel a lot where your speed doesn’t vary quite as much, 700c is likely the right choice for you.
Additionally, if you do a lot of all-out efforts in shorter, flat(ish) races on light gravel, then maintaining speed is often more important than accelerating, and so 700c might suit you a little better.
So, which is better: 650b Vs 700c?
This question ultimately will come down to where you ride your bike, and how much variety you want in your rides.
If you like to mix it up with asphalt, gravel, and a bit of singletrack, then 700c is probably the best choice.
However, if you prefer to stick to off-road, loosely packed, muddy singletrack or MTB trails, then 650b will likely provide you with a more comfortable and stable experience along with a more durable set of wheels.