Mason Definition 2 Rival 1X review

We've tested the latest update of the Mason Definition alloy "multi-discipline" bike. The Definition 2 has had a subtle makeover, incorporating new technical features

(Image credit: Cycling Studio)
Cycling Weekly Verdict

The Mason Definition 2 makes a number of changes to bring the design up to date with recent trends, but carries forward the original Definition’s versatility. It’s beautifully finished, comes with a quality spec well suited for UK riding and has the versatility to cover everything from fast club runs to bikepacking adventures.

Reasons to buy
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    Well-thought-out frame and spec for UK riding

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    Beautifully finished

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Reasons to avoid
  • -

    More expensive than a mainstream brand

You can trust Cycling Weekly. Our team of experts put in hard miles testing cycling tech and will always share honest, unbiased advice to help you choose. Find out more about how we test.

When Mason Progressive Cycles brought out the original Mason Definition in 2015, disc brake road bikes were a bit of a rarity, as was the Definition’s geometry, designed to work off-road as well as on. Three years later, these features are now commonplace in non-racing road bikes. Time for a refresh of the Mason Definition to keep it ahead of the curve.

The original alloy Mason Definition was matched by the Mason Resolution steel machine, which we’ve also tested. Mason has found that, although superficially similar, the two bikes were used for rather different purposes, with the Definition tending to be selected by slightly younger riders looking to ride faster.


The Mason Definition 2 frameset is built in Italy of custom Dedacciai aluminium alloy tubing. There’s full internal cable routing through to the chainstays, using Mason’s flexible port system, which caters for mechanical, hydraulic and electronic groupsets.

Mason Definition

Subtle branding on Mason's bikes is best viewed from behind
(Image credit: Cycling Studio)

Mason uses a wide down tube and oval section top tube for rigidity. The bottom bracket shell is designed specifically to provide extra weld area. It is wide enough for the cable runs to pass internally, but steps down at its ends, so that it accepts a standard BSA threaded external bearing bottom bracket. The chainstays and seatstays have bespoke curved shaping to add a bit of compliance.

The original Mason Definition used quick-release axles and post0mount disc brakes, but Mason has used the refresh to equip the Definition 2 with thru-axles, 142x12mm rear axle spacing, and flat mount calipers – items which have now become more or less standard on disc brake road bikes.

Aperture 2 fork comes with replaceable threads for the thru-axle
(Image credit: Cycling Studio)

Mason has also completely redesigned its Aperture all-carbon fork, again with thru-axles and flat-mount brakes, also adding extra tyre clearance. It’s more sinuous than the original and the axle threads are replaceable.

The Mason Definition’s go anywhere credentials are enhanced by a complete set of mounts for mudguards and racks, with the mudguard mounts on the inside edges of the fork and seatstays, to make them less noticeable. There’s room to fit tyres up to 30mm wide, with clearance for mudguards, or 33mm without guards.

The Mason Definition frameset is available in black, blue or this new Element Grey. Mason has even considered the placement of logos so they don’t shout out at you but are subtly displayed from the side and rear. There’s a smart embossed head tube badge.


You can order the Mason Definition 2 as a frameset only for £1,150, in sizes from 50cm to 60cm. But Mason also offers the Definition 2 as a complete build in a range of specs.

Top of the spec tree is the £4,995 SRAM Red eTap build. Another change since the original Definition was launched is the increasing acceptance of single-ring groupsets on road bikes. The other specs offered reflect this, with SRAM Force 1 HRD and Rival 1 HRD options, alongside two ring Ultegra Di2 Hydro, mechanical Ultegra Hydro or 105 Hydro. The SRAM builds come with SRAM’s recommended 160mm disc rotors, whereas Shimano builds use 140mm IceTech rotors.

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This Rival 1 build has a 46-tooth chainring and 10-42 cassette for a wide range and enough high ratios for road riding but the grunt to climb steeps on unmetalled surfaces.

Mason Definition

The Definition 2 comes with two SRAM single ring options
(Image credit: Cycling Studio)

Mason has always paired with Hunt Bike Wheels, who produced the Mason x Hunt 4Season Disc wheelset especially to meet Mason’s requirements. The wheels come with wide, tubeless-ready rims, great ride quality and a robust build. Opt for SRAM Red eTap and you get the option of Hunt 30CarbonAero Disc wheels.

There’s a Deda alloy cockpit, 27.2mm Mason carbon seatpost and Fabric saddle to complete the build. But one advantage of buying a Mason is that you can talk to Dom Mason, take a test ride and specify components to meet your own needs.

Riding the Mason Definition 2

Mason has the knack of producing bikes which feel engaging, while still giving you a comfortable long distance ride, making the Definition 2 a joy to pilot. It feels fast and lively on flatter roads, easy to climb and confident on descents, with the assurance of hydraulic disc braking.

The wide Schwalbe G-One Speed tubeless tyres fitted are a £100 upgrade and give plenty of grip too, without any noticeable additional rolling resistance over a narrower slick. Coupled with the Definition 2’s stable handling, they cope well with muddy paths with a gravel base. Although there’s not quite the grip to handle the muddiest bridlepaths, you have enough off-road ability to expand your riding off tarmac.

Mason Definition

Mason's frame ports will cater for any groupset
(Image credit: Cycling Studio)

The tread is a close array of small, round knobs. On wider Schwalbe tyres with this tread pattern we’ve experienced clogging in muddy conditions. But being quite narrow, the tread on the Mason Definition tends to resist mud build-up and clear easily. There’s plenty of clearance in the frame to keep mud off stays and fork legs too.

>>> How much damage can a tubeless tyre take? (video)

The Schwalbe G-One Speed tyres are a bit more delicate than some others, though, and I had one puncture that was fussy to seal.

Mason Definition

Mason specs the Fabric Scoop Shallow saddle as standard
(Image credit: Cycling Studio)

I’m not a fan of the Fabric Scoop Shallow saddle. It doesn’t seem to have enough padding in quite the right places to suit my sitbones. A swap-out made things more comfortable.

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At 8.5kg, the Definition is some 800g lighter than the steel Resolution which we tested a couple of years back. So it’s that much quicker off the mark and when climbing, although it shares the same geometry. But the alloy frame gives a more lively ride, rather than the Resolution’s more relaxed feel.

The single-ring groupset with its 46-tooth chainring may sound as if you’re going to run out of ratios, but the largest 42-tooth sprocket gives you a lowest gear equivalent to a 31 tooth sprocket with the 34-tooth chainring on a standard compact double chainset. At the other end, the 10-tooth sprocket gives you a slightly higher ratio than a 50x11.

So you’ve got a good spread of ratios without the overlaps which a double-ring set-up will produce. The single ring makes for a simpler groupset without the extra complication of the front mech. It also saves a bit of weight. You soon get used to shifting with one hand and SRAM’s single up and down lever.


Although Mason’s bikes are not strictly bespoke as they come in defined frame sizes, you’re getting something close to a custom build. There are predefined specification options, but with bikes assembled to order in the Mason Bike Barn in Sussex, you can have as much input into the final product as you want.

Mason Definition

Go-anywhere capability is enhanced by rack and guard mounts
(Image credit: Cycling Studio)

Dom Mason is also something of a perfectionist. Not finding a fork to meet his requirements, he designed his own and found someone to build it, for example. You can discuss the pros and cons of a desired spec with Mason and his small team and take out a bike for a ride before you order.

>>> Mason Bokeh review

Despite the low volume, Mason puts its bikes through the same testing regime as mainstream manufacturers.

So you wouldn’t expect to pay an equivalent amount for a Mason as for a major brand’s machine with comparable spec. But you are getting something unique and carefully designed to meet the exigencies of UK riders.

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