Diamant 140 review: a fun retro-modern commuter bike built to get rough, but it's too heavy

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You may be forgiven for not knowing much about Diamant Bikes. Even though the German brand started out in 1885, Diamant bikes are rarely seen outside of mainland Europe. However, the brand (which was acquired by Trek in 2002) has a range of affordable yet rugged urban bikes.  

The 140 comes very much from the rugged side of Diamant’s range and is named in celebration of the brand’s 140^th anniversary – it launched on Diamant’s birthday. 

In testing, it has proven impressively capable off-road and a solid package. However, priced at £1,700 / €1,899, its excess weight holds it back from competing with the best options at this price point. 

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Diamant 140 frameset 

The frame is made from Alpha Aluminium – this is Trek's own aluminium recipe. The similarly priced Trek Checkpoint ALR uses premium-grade 300-series Alpha alloy. 

The 140’s frame is well appointed, with mounts for racks, mudguards, a top-tube bag and four sets of bottle bosses (including on the underside of the down tube and top tube). 

The driveside seatstay splits, so you can convert the 140 to a belt-drive system (a toothed, carbon-fibre reinforced belt instead of a traditional metal chain that requires less maintenance). Diamant also offers a flat-bar variant of the 140, called the Mahon Style Plus, with a belt drive. 

Up front is an SR Suntour NCX32 fork, offering 75mm of coil-sprung suspension. The fork has a preload adjustment and a lockout function to tailor its behaviour. 

Both the frame and fork use traditional quick-release dropouts – a rare sight on any 2025 bike, not to mention one designed for off-road, with thru-axles now de rigueur.  

The frame is well-finished, with a nicely realised retro-modern paintjob, and the gold-anodised hardware gives it a quality edge that belies its modest price tag. 

Diamant 140 geometry 

The 140 is based around smaller 650b wheels and comes with very generous 2.5in tyre clearance.  

The head angle is a relaxed 69 degrees, matched to a fairly standard 73-degree seat angle. These are combined with a long 407mm reach and a tall 626mm stack on my size-large test bike.  

The long 468mm chainstays and generous 1,158mm wheelbase should add up to a bike with steady, relaxed handling. The use of a short 90mm stem across the full range of sizes will, however, help to liven up the handling. 

Diamant 140 specification

The 140 has an interesting build, with some budget choices that bring it down compared to rival gravel bikes for less than £2,000.

The drivetrain combines a long-cage Shimano GRX 822 rear derailleur with a 12-speed, 10-51 tooth SLX cassette from Shimano’s mountain bike stable. This is combined with an SLX chain driven by a budget Prowheel crankset with a single 42-tooth chainring. 

Braking also comes from Shimano, with GRX610 shifters and GRX410 brake calipers.

The 140 rolls on alloy Bontrager Kovee rims built onto Shimano Tourney quick-release hubs. The Kovee rim is tubeless-compatible, with a broad 23mm internal width. These are wrapped with very off-road-focused tubeless-ready Schwalbe Nobby Nic tyres in a large 2.4in width. It's an odd choice for a commuter bike, but very welcome when it comes to winter off-roading.

The contact points are a highlight. Up front, a well-shaped Bontrager Elite gravel bar in a generous 44cm width is held in place by a nicely finished Elite stem that’s Blendr-compatible – fitting a range of Bontrager mounts and lights.

Diamant also includes a Racktime Viewit steerer-mounted front rack. Again, this is an odd choice for a commuter bike given its small capacity, although it’s a practical option for bikepacking because its 5kg load capacity will easily take a sleeping bag or a large front roll pack.

At the rear, a simple Bontrager alloy seatpost is topped with the great-looking and comfortable Brooks C17 Cambium saddle.

Diamant 140 ride impressions

The 140 is a fun bike to ride, thanks to the combination of stable and confident handling, a plush fork (once you’ve dialled it in to suit your weight and riding), and great tyres for mixed conditions.

The downsides, though, are middling shifting performance, noisy brakes and a lot of weight to pull up hills.

Let’s concentrate on the 140's upsides first. The combination of the tall front end, compact reach and that 75mm-travel fork makes for a bike that’s a blast to ride off-road. Combine that with the massive Schwalbe tyres with their all-conditions tread, and it results in a bike that has near-mountain-bike handling chops when it comes to trails and singletrack.

The 27.5in/650b wheels make the bike feel a lot nimbler than its almost-15kg weight would suggest. It also feels quicker than it should out of the blocks.

The simple fork works well enough once you’ve put in the effort to dial it in to your preferences. It, of course, would be completely outclassed by a mid-range mountain bike fork, with its 2.5kg weight adding to the Diamant’s overall heft. 

I’d like to see Diamant put out a non-suspended version of the 140, though, or offer it with a better budget mountain bike fork – even an entry-level fork, such as a 27.5in-wheel-compatible RockShox Recon, would save over half a kilo compared to the Suntour fitted here.

That said, on the rootiest, rockiest trail sections of my test loop, the Suntour was a boon, squashing the front end through the lumps and bumps, and enabling more speed than either the Whyte Verro or Trek Checkpoint ALR 5 Gen 3 I tested it alongside.

The mish-mash drivetrain offers a good range, through the 42-tooth chainring matched with a very wide 10-51-tooth, 12-speed cassette.

I certainly appreciated the 42-51 when riding steep climbs, and the big 42-10t gear meant getting the most of the momentum afforded by the extra mass when descending.

I got the occasional sluggish upshift from the drivetrain with the chain labouring, especially in the higher reaches of the cassette. Downshifts, similarly, were on occasion choppy and noisy, with the chain taking half a crank turn to settle, especially when shifting under load.

The braking is good and powerful, although very vocal – not something I usually expect from Shimano’s GRX brakes (especially with huge 180mm rotors). That could well be down to the Diamant 140 using quick-release skewer hubs rather than the extra rigidity afforded by modern thru-axles.

The downside of the smaller-diameter wheels is, compared to a 700c wheel, you run out of legs when moving at higher pace on the road.

Riding with 700c-equipped friends, I was left off the back, pushing harder to maintain average speeds up around 20mph-25mph on the flat. Then, when the road or dirt starts to rise, it's compounded by the extra heft the Diamant carries.

So, the trade-off between rough trail prowess and on-road speed, be it for commuting or otherwise, is much more marked on the Diamant 140 than on its rivals here.

Diamant 140 bottom line

The Diamant 140’s frame has lots of versatile potential, thanks to being hub-gear and belt-drive ready. 

The problem with the 140 is, while it's a lot of fun to ride on tough, technical terrain and trails, it's harder work than its simpler, stripped-down rivals. 

The Diamant is different and it stands out in a packed market. It does, however, desperately need to lose some of the excess mass because the advantages I gained when taking on switchback-strewn singletrack and fast, lumpy downhill trails weren’t enough to balance out the hardships of climbing with nigh-on 15kg underneath me and the effort it took to stay at group riding pace on rolling tarmac.

As a commuter bike, it's comfortable and easy to ride; as a commuter-cum-performance bike, it's outclassed in this company. If you’re looking for an affordable bike that’s this capable off-road, you may be better served by an affordable hardtail mountain bike, or great gravel bikes such as the Whyte Verro or Marin’s Gestalt X10.

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