A departure from their road ancestors, gravel bikes offer a choice of wheel sizes: the standard 700c as seen on road bikes, or the slightly smaller 650b – with many gravel frames designed to accommodate the two.

You can also often choose between these gravel wheel sizes when ordering your new gravel bike setup.

What are the differences between these hoop sizes and what are the pros and cons of each? Should you have a set of each with different tires to tackle different terrains?

Here we take an in-depth look to help you decide which gravel wheels are best for your rig.

What is the 650b?

What does 650b actually mean? The name of these wheels – which are essentially the same as 27.5in mountain bike wheels – are derived from a French sizing system, as is 700c (29er equivalent).

The number refers to the approximate diameter of the wheel including the tire, while the letter refers to the approximate width.

We use the word approximate here, because this measurement includes the tire, the size of which can vary considerably depending on the profile of the tire. To be more precise, rim bed to rim, a 650b wheel is 584mm in diameter, with a 700c rim measuring 622mm. A little less catchy, isn’t it?

However, when we talk about 650b wheels for gravel riding, we usually associate this smaller wheel size with larger volume and wider tire widths, as there is usually more tire clearance in the frame for accommodate that thicker rubber compared to the 700c wheels.

Therefore, compared to a 700c wheel with a narrower tire, the effect of the reduced rim diameter of the 650b wheel is lessened due to this increased tire size. This is because the bearing diameter of the two different configurations is usually more similar than you might think.

Benefits of running 650b wheels on a gravel bike

650b wheels are typically run with wider tires—in the range of 45mm to 2.1 inches (53mm)—compared to 700c wheels.

This allows riders to reduce tire pressure, which improves grip and comfort. A larger air cushion can also reduce the risk of a pinch flat, especially when configured tubeless.

Improved grip comes in handy on the roughest trails, while increased comfort is especially useful for long, multi-day bike rides.

Just as some shorter riders tend to opt for 650b tires on the road for better handling proportional to frame size and reduced toe overlap, this can also be the case when it comes to riding dirt. gravel.

Finally, 650b wheels tend to be stronger than 700cs, as the shorter spoke triangle leads to a sturdier build.

Cons of running 650b wheels on a gravel bike

Since 650b wheels and tires for gravel riding are relatively new, the choice is slightly more limited, although that is improving.

Most 650b tires will be higher volume options (45mm and up) and generally feature a higher tread level, such as the 47mm WTB Sendero, which is basically a small XC tire.

If you already have a 700c wheelset, you will have to shell out for a 650b alternative. Luckily, there are a range of options on the market to suit most budgets, from entry-level versions to bespoke, lightweight, race-focused carbon wheels.

Don’t forget you’ll also need inner tubes to match your new wheels – either for your standard setup or a spare if you have a tubeless setup problem. Check out our complete guide to fixing tubeless tires before hitting the trails if this technology is new to you.

Advantages of 700c wheels on a gravel bike

As 700c wheels have been the norm for a long time there is a good availability of gravel specific wheelsets on the market.

Aside from standard axle incompatibilities, there’s nothing technically stopping you from using a road or mountain bike wheelset on a gravel bike.

However, remember that you will need to check the internal diameter of the rim before buying, as this largely determines the suitability of a wheelset for use with gravel tyres.

To be specific, ETRTO tire standards (revised 2020) recommend 21mm inner diameter rims for 29-34mm tyres, 23mm for 35-46mm tyres, and 25mm for tyres. from 47 to 57 mm (up to 2.2 inches).

In addition to good wheel availability, there is also better 700c tire availability, along with a host of different widths and tread options.

Many people claim that a larger diameter 700c wheel will provide easier rolling, just like a 29er mountain bike setup. However, it’s more nuanced than that when it comes to gravel.

Of course, if the 700c and 650b wheelset were set up with the same tire width – say 40mm – then the 700c wheelset would have a larger outer diameter, and therefore greater rollover.

However, most people go for a wider and bulkier tire for the 650b wheels, which greatly reduces this difference between the external diameter of the configurations, and therefore the impact on the rollover.

The other main benefit of 700c wheels that is often cited is reduced rolling resistance, which is why 700c is the more popular choice when it comes to gravel racing.

This is a bit of a broad generalization and depends on both the tread and width of the tires chosen, as well as the tire pressure.

For a more in-depth look at rolling resistance and tire choice, check out Simon von Bromley’s comprehensive guide.

Disadvantages of using 700c wheels on a gravel bike

The downside of 700c wheels is that you can be significantly limited in the maximum tire width you can install. This can also extend to mud clearance and space limitations for traditional fenders.

It depends on the frame design, however, and many modern gravel bikes will have plenty of tire clearance on 700c wheels.

650b or 700c, which is right for you?

As with all cycling gear choices, the best wheel size for your gravel bike will depend on the type of gravel riding you like and what you hope to get out of your time off the tarmac.

Want to rumble and hit mountain bike trails, or want to traverse a mountain range with everything you’ll need for a week? Try 650b.

Looking to go fast on hard ground and smoother tarmac without compromising on speed? 700c will probably be best for you.

There is so much more to this question than just wheel size, as all of these attributes also depend on your tire choice and how that interacts with wheel size.

It seems like preferences are also changing, as WTB’s European marketer James Heaton explains. “Our wider 700c gravel tires are gaining popularity. Frame designers are creating bikes with more and more tire clearance and this allows more riders to enjoy the benefits of larger volume tires.

“It used to be largely riders with 650b wheels who could benefit from the extra comfort and grip that bigger tires provide, but it seems the world of floating fun is slowly opening up to those with bigger tires. 700c wheels too.”

Ollie Gray, road and gravel brand manager for Hunt Bike Wheels, seems to agree. “It’s common to see clearance for 700×45 now, whereas a few years ago it was necessary to use a 650b wheel if you wanted a high volume tire. Frame design has caught up, so using bigger wheels with bigger tires is easier than before.

According to Ollie, the sales numbers show that 700c seems to be edging out 650b as the de facto drop-bar wheel size. “However, I don’t think the 650b is going away,” he continues, “and honestly, I do think a 650b wheelset can be a bit of a no-brainer when it comes to gravel bikes. is a very simple way to make one bike look like two.