In the quest for ever wider, squishier rubber on my gravel bike I found myself in the market for a set of 650b wheels.

The Cannondale Topstone can clear 2.1" mountain bike tyres in 650b size, and I wanted a piece of that action.

There are plenty of excellent off the shelf options when it comes to 650b wheels but I fancied something custom so turned to my trusted builder, Colin at AM Bike Co for advice.

Colin has got me out of a jam a couple of times: first by rebuilding a wheel that I managed to smash on the Lakelander Gravel Grinder in 2022, and then building up a lovely set of hoops for my MTB. He's a perfectionist - a quality I think many wheel builders share - and as a biker himself is happy to share advice and patient in discussing the best spec for a customer's requirements.

I'd spotted some carbon rims from Light Bicycle, the XC725, that seemed ideal. Designed for cross country mountain biking, I figured they would be more than tough enough for gravel despite a feathery weight of 285g apiece.

Light Bicycle are a Chinese brand, they're not widely known in the UK but Colin was interested to check them out. The XC725 are a shallow-profile rim: just 23mm deep, but with a 25mm internal width in line with the current trend for gravel-oriented wheels.

They are made of Toray T700 and T800 carbon fibre and come in a Standard or Flyweight version, with 24h, 28h, 32h and 36h spoke options. The Standard version is reinforced and weighs 345g (60g more than the Flyweight); it is rated for rider weight of 100kg, compared with 90kg for the Flyweight.

The rims come with a five-year warranty as standard, with the option to upgrade to lifetime warranty at a surcharge.

For hubs, Colin was happy to recommend his favoured DT Swiss. We agreed to pair the rims with a set of DT Swiss 240 straightpulls for what should make a reliable, lightweight build.

I suspect Colin would have preferred me to go for more than the 24h spoke option, but we compromised slightly by speccing DT Competition spokes to add stiffness over DT Aero Lite bladed spokes. (Aero Lite also cost 3x as much as Comp so I was easily persuaded.)

I got the hubs posted to Colin's workshop in Antrim and the build was scheduled in.

A few days later I got a message: "Thought you'd like to know this wheelset's weight... 1214g!"

That's an eye-catching weight for a gravel wheelset - and this was with brass nipples. Using alloy would have brought the weight below 1200g.

You get nothing for free though: Colin noted that the wheels were slightly flexy under side to side pressure, justifying the use of the slightly heavier spokes.

I collected the wheels and popped a pair of Vittoria Mezcal 650x2.1 tyres on. They sealed first time on the hookless rims, and immediately gave the Topstone a more rugged look.

Hitting the local MTB trails for a test ride, the difference over my previous 700x45 tyres was significant. It felt like cruising aboard a monster truck: the added volume and grip is a game changer on loose rocks or mud. My gravel bike had become a dropbar MTB.

The tyres are heavier of course, but the low weight of the wheels themselves offsets this to some degree: they spin up reasonably fast, and rear hub engagement is equally rapid with DT's Ratchet EXP system.

On rougher gravel the trade-off is a no-brainer, it's well worth it for the added confidence, stablilty and grip that wider tyres give you.

Out on the trails the difference is instantly noticeable.
Out on the trails the difference is instantly noticeable.
The 2.1' MTB tyres add improved comfort and traction off-road.
The 2.1' MTB tyres add improved comfort and traction off-road.
I've now spent 10 months on these wheels, including a winter hacking the wheels over pretty rough terrain, and they havent missed a beat. They're still true as the day they were built - a testament to Colin's diligence - and the Light Bicycle rims have proven as tough as you'd hope.

The XC725 may be a featherweight on the scales, but they hit like a heavyweight on the trails.

The diameter of the smaller wheels with 2.1 tyres is almost identical to my 700c wheels with 32mm road tyres. They handle well, but there is a noticeable penalty in terms of speed when you leave the trails and hit roads or even light gravel tracks.

In those conditions the 700c wheels with a 40-45mm tyre still have the edge. But the 650b wheels and chunky tyres are so much fun on the rough stuff that I find myself leaving them on more often than not.

When the going gets tough bigger tyres really pay off.
When the going gets tough bigger tyres really pay off.
Up to a point anyway...
Up to a point anyway...
As for the flex Colin observed in the wheel stand, I can't say I've noticed this in practice. I've not tried any loaded bikepacking on them yet but it's on the list - that was one of the main reasons for having these wheels built. I'd have no hesitation in trusting the XC725 on something like the GranGuanche Audaxor any multi-day off road tour.

If you're interested in adding some variety to your gravel arsenal, you can buy the rims either by themselves or as a wheelset from Light Bicycle.

The XC725 rims are priced £208 apiece at current exchange rates. A pair including shipping to the UK, with tax prepaid, comes to £479.

Light Bicycle also offer a wide range of custom builds, for example you could get a set laced to Hope Pro 4 hubs (wheelset weight 1532g) for £778.

Or, if you happen to be based in Northern Ireland, I would highly recommend dropping Colin a line at AM Bike Co. A wealth of knowledge and a pleasure to talk bikes with, he is also meticulous in his work and will build you a set of wheels you can depend on.

Find out more about Light Bicycle at

Get in touch with AM Bike Co at