The vast majority of gravel bikes accept either 700c (standard road size, actual rim diameter equal to 29in mountain bike rim) or smaller 650b wheels (actual rim diameter equal to 27.5in mountain bike rim). 

Many framesets are designed to accept both sizes, with the option to fit wider tyres if you opt for 650b. This works because the rolling diameter of a fat 650b tyre (e.g. 650b × 47) is similar to that of a 700c wheel fitted with a much narrower tyre (around 700 × 28 to 30mm, approximately).

Having said that, you can’t assume that both sizes will work. A frameset designed for 700c wheels may accommodate the diameter of chunky 650bs, but lack the clearance at the stays or fork for the width of the tyres. 

It’s best to follow manufacturer recommendations here, to avoid costly disappointment.

Choosing between 650b or 700c largely comes down to personal preference but, if you’re unsure which way to go, think about what size tyres you’re most likely to want on your bike.

If your gravel riding is more like all road, you might want tyres in the sub-40mm range that will work well both on and off tarmac. 

You’ll have more tyre options if you opt for 700c in this case and you’ll be able to go as narrow as 28mm for pure road riding (usually – so follow manufacturer recommendations here), or about as wide as your frame will take at the other end of the spectrum (few gravel frames will accept a tyre larger than 700 × 45mm).

If you want as much tyre volume as possible and your gravel riding sometimes resembles mountain biking, 650b makes a lot of sense. 

A 650b × 47mm tyre is balloon-like in its ride quality and some frames will let you go larger still, edging fully into mountain bike territory.

There are, however, very few 650b tyres under 38mm wide and the rims themselves tend not to be designed for narrower ones anyway, so do consider if you might want the option to go narrower for road riding in the future. 

A very small minority of gravel/adventure/touring bikes, such as the Surly Long Haul Trucker Disc, are designed to take 26in tyres, i.e. the old standard for mountain bikes. 

If you’re touring in parts of the world where 26in is still the de facto standard for adult bikes, this makes sense from a spares point of view. 

Otherwise, there isn’t a compelling reason to favour 26in over the more mainstream sizes for gravel, and the latest gravel tyres are typically only available in 700c and/or 650b.

Tubeless tyre compatibility

We’re big fans of tubeless tyres because you can run them at lower pressures without the risk of pinch flats. 

If you’re shopping for a new gravel wheelset, it makes sense to at least have the option of going tubeless, even if you don’t plan to do so initially. 

Tubeless adds complexity at the setup stage, but offers real benefits when it comes to riding. 

You can run lower pressures for grip and comfort without the risk of pinch flats (a particular concern if you’re riding relatively low-volume tyres on mixed surfaces) and sealant will take care of smaller punctures.

Many wheels will come with tubeless valves and tape (if needed) as standard, but if they don’t, you’ll need to budget for them as an extra. 

Weight and durability

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As well as having wider rims, wheels designed primarily for gravel are likely to be burlier than their road counterparts, although this is a generalisation. 

They may have higher spoke counts and some manufacturers will opt for better-sealed hubs and/or larger bearings for durability. Super-lightweight road hubs are not the best choice if you’re planning to get your gravel bike muddy and wet.

As a result, dedicated gravel wheelsets tend to be heavier than road ones, although the difference may not be significant in the scheme of things. 

Rim materials

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As in other riding disciplines, carbon is the money-no-object choice and the best option in terms of overall performance and weight. 

If you want gravel wheels with aero credentials, the case for carbon is stronger. However, it comes at a huge price premium over aluminium (or “alloy”), which is arguably far better value for money, offering virtually all of the performance for as little as half the price, or less. 

Carbon is nice to have, but absolutely not a necessity. 

Axle and brake rotor compatibility

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The gravel bike market has more or less settled on 12mm thru-axles front and rear as standard, but there are plenty of existing bikes out there with different setups, e.g. 15mm for the front, or old-school quick-release skewers.

When choosing a new gravel wheelset, make sure its hubs can be adapted to fit your frame and fork, and check whether the parts needed are included as standard or need to be bought separately. 

Disc hubs are designed to accept either six-bolt rotors or Center Lock ones. If you’re switching from one to the other in the course of a wheel upgrade, you’ll either need to buy new rotors or, alternatively, there are adaptors to fit six-bolt rotors on Center Lock hubs, and vice versa. 

Incidentally, we wouldn’t base our choice of wheels on the type of rotor used, but, for what it’s worth, Center Lock rotors are much quicker to install and remove. 

Note that Center Lock rotors require a lockring, which may or may not be included with the wheels (or with the rotors themselves). Some use an internal cassette style tool for installation, while others need an external bottom bracket (BB) type tool, of the kind used for Shimano BB cups.

Lockring threads are standardised, but we’ve encountered lockrings that don’t work on certain hubs because of the specific design, so check if there’s a recommended one for your wheels. Usually, that’s because the hub body is too wide to fit an internal tool, in which case you’ll need an external flange lockring and the requisite BB tool.

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