Mason ISO




  • Go anywhere capability
  • Set up for off-grid load lugging


  • Not the fastest on road
  • Doesn’t look pretty

Price as reviewed:


Mason goes far off grid with the new InSearchOf, or ISO

Mason Progressive Cycles founder Dom Mason dubs his bike brand the #FastFar company. The new Mason InSearchOf, or ISO – looks to push the #Far side of that beyond where gravel bikes are comfortable. The Mason ISO was born from Dom Mason’s own exploration of the limits of the Mason Bokeh.

According to Mason: “We found ourselves taking the Bokeh to territory and terrain that we had never imagined riding with a bike like this. Josh [Ibbett] found himself deep in the Mexican desert, fully loaded in deep sand.

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“I found myself smashing down blue runs in the French Alps and linking runs together on isolated, steep, Rocky Mountain trails. The Bokeh handled this stuff incredibly well, it was amazing fun but it got us thinking again and after a long distance call from Josh (he was actually in his bivvy bag way out in the desert), I started sketching.”

Big tyres

The ISO takes things one step further than the Bokeh, with clearance for 2.4in 700c tyres. Drop to 650b and that increases to 2.8 inches.

That’s a lot of rubber on the road – or rather the trail, or in my case, with water running above the axles, the river bed.

Mason ISO

You get the option of these 2.4in 700c WTB Ranger tyres or a 2.8in 650b

The astonishing thing about the ISO is just what you can tackle when riding it. So wet, muddy or compacted chalk uphills which would have defeated me on just about anything else I could just roll up on the Mason ISO. Likewise, you float through deep sand and all but the deepest. sloppiest mud holes.

That’s achieved with the tons of grip from the 2.4in WTB Ranger 700c tyres, or the even greater grip from the larger contact patch on the 2.8in Ranger 650bs. The Ranger has a tread with large, well-spaced knobs, so you get lots of traction. The steepest, wettest mud did provoke wheelslip, but the ISO took me way beyond my usual terrain.

As well as the huge tyres, the ISO boasts the gearing to match. The SRAM Force 1 cassette has a 10-42 range and is coupled to a Truvativ 34-tooth chainset with carbon cranks. So you’ve got a bottom gear of lower than 1:1  to spin up steep, off-road terrain. There’s a Rival 1 build available as well.

The Mason ISO does equally well on descents too: with so much air volume and grip you can just roll confidently over ruts, runnels, roots, rocks and off camber. Mason ups the braking power by fitting a 180mm rotor up front and a 160mm at the rear to handle long, hard braking when heavily loaded without overheating.

34-tooth chainwheel coupled to a 42-tooth largest ring means you can ride up walls

There was nary a squeal from the brakes on steep descents off the South Downs, although admittedly it was February. You can fit a dropper post if you want to get your seat out of the way. Operated using the spare left shifter, the cable runs along the top of the down tube externally, then disappears into a port in the bottom of the seat tube.

As well as the 700c build, I rode a 650b bike with a dropper. That combination lets you hammer down fast descents with a lowered centre of gravity. Or you can move the saddle right out of the way and push your weight far back on really steep downhills.

There’s routing for different shifter cable formats in the frame including electronic or for a front mech if you want one. Or you can blank the ports off to go eTap. Although Mason offers the ISO in Force 1 and Rival 1 builds, it’s happy to play with the spec to meet buyers’ different requirements.

The spec to handle the rough stuff

To support those massive tyres there’s a choice of Hunt wheelsets: the TrailWide 650b wheels boast 30mm internal width rims while the equally wide Mason x Hunt The Search 700c wheels come with the option of a front hub dynamo for an extra £150. There’s internal routing through the fork leg for the dynamo cables.

That choice hints at the Mason ISO’s other life. It’s a bike designed not only for the weekend warrior in search of more extreme terrain, but the confirmed bikepacker looking to take on fully loaded off-road adventures.

That’s backed up with as many loading points as you can shake a bike bag at. The carbon fork is riddled with bolts – a total of 12. There are even more on the steel frame – a mix of Dedacciai Zero and Reynolds 853 custom profiled steel tubing – to support bottles, racks and bags as well as mudguards.

Mason ISO

Mason ISO’s front mudguard helps carry the load on the bars

Plus, the supplied composite front mudguard is extra-rigid, has four mounting points and is designed to support up to 2kg, so you can load up the bars and front end too. Mason has designed an optional metal front rack for even more carrying grunt.

Roadie features on the Mason ISO are principally the rigid fork – and even that can be swapped out for a suspension fork if you wish – and the Ritchey VentureMax drop bar. The bar is wide on the tops with a slight rearward sweep. It’s flared at 24° to an even wider 50cm or so in the drops, which are shallow.

The ISO’s fork is tall to accommodate all that rubber so even with quite a short head tube the bar ends up quite high. That, along with the shallow bend, means you can easily ride in the drops for road or off-road descents without compromising the bike’s balance and steerability. There’s a short, mtb-ish 8cm Ritchey alloy stem to help with the point-and-shoot feel.

Mason ISO

Mason ISO is probably the first bike to use a flatmount brake caliper with a 180mm rotor

Other mtb-like features include the use of Boost 15x110mm front and 12x148mm rear axles and a 73mm wide DUB threaded bottom bracket to give extra rear tyre clearance (yet another axle size, to give wider compatibility with different bottom bracket standards, it’s used too in the new SRAM Red eTap AXS groupset). The curved down tube adds front end clearance and room for a suspension fork to bounce too.

As well as capability, the ISO pushes the envelope in its spec. Dom Mason points out that there was no published standard for using a flat mount caliper with a 180mm rotor, so he had to work out just where to position it on the fork for it to work correctly.

But the ISO isn’t just a mountain bike with drop bars bolted on. Mason has adopted a more roadgoing geometry so the ride position is familiar for a road rider and you are well positioned to ride seated on the flat and when climbing.

Riding the Mason ISO

I’ve talked about the off road ride on the Mason ISO. It’s fair to say that that’s its natural terrain. But most rides, at least in the southern UK, will involve some metalled roads. You can hum along quite nicely on the flat, with hum being the operative word – there’s quite a bit of noise from the knobbly tyres.

With its 10.6kg unloaded weight and big tyres, the ISO is never going to fly up hills. On the tarmac, it’s a question of sitting in on the Fabric Scoop saddle, mounted on its Mason Penta carbon seatpost, and using that low gear range to spin up the gradient, however steep it gets.

But the tyres mean that it’s super-planted once you start on the way down, no matter how sketchy or loose the surface becomes. I find the ride and hand position on a drop bar bike, coupled with the option to ride on the tops or the lever hoods or in the drops works better for me than the single position, horizontal grips on a mountain bike, particularly on longer runs and when you have to take in some tarmac.

In conclusion

So the Mason ISO is a supremely competent ride if you’re wanting to tackle more radical terrain on a drop bar bike, either for a quick outing or a longer, multi-day trip. It gives the stability and confidence to keep riding through, over, up and down whatever gets in your path.

Mason ISO

Dynamo front hub option keeps you powered up in the backwoods

But it has to be said that I’ve received mixed reviews for the Mason ISO’s looks. Loaded up and ready to disappear into the backwoods, it looks the business and ready for anything. But your roadie friends might think it’s a step too far off the beaten tarmac.

At £3,490, the Mason InSearchOf isn’t a cheap option. But if you are looking to tackle more extreme off-road, while still having the ability to roll along comfortably on tarmac, or if you plan some serious bikepacking expeditions, it lets you go further and more extreme than just about any other drop bar bike.


The Mason ISO will take you into territory where a dropped bar bike has no right to be. It’s great fun to ride, super-planted and has the versatility for more extreme bikepacking as well as messing around in the woods. But its extra-wide tyres mean that it’s a bit sluggish on tarmac.


Frame: Dedacciai Zero/Reynolds 853 steel
Fork: Mason HotShoe carbon
Size range: 42, 46, 50, 54, 58cm
Size tested: 54cm
Weight: 10.57kg/23.3lb
Groupset: SRAM Force 1/Truvativ Stylo Carbon
Gear ratios: 34, 10-42
Wheels: Mason x Hunt The Search Dynamo 700c or TrailWide 650b
Tyres: WTB Ranger 2.4in 700c or 2.8in 650b
Brakes: Force HRD 180/160mm rotors
Bar: Ritchey VentureMax WCS
Stem: Ritchey WCS Trail
Seatpost: Mason Penta 31.6mm carbon
Saddle: Fabric Scoop Elite alloy railed