Surly Karate Monkey Bike Review

Surly Karate Monkey Bike

The Karate Monkey promises a resilient and lively ride on all sorts of gnarly terrain. Described by its makers as a canvas for whatever dirty masterpiece your brain might cook up, it can be adapted in myriad ways and will roll happily on either 29er or 27.5+ wheels.

Set up with smaller diameter hoops and big tires, this custom- built option is produced by U K distributors Ison using parts from its house brands Gusset and Halo.

First impressions

OK, who let this one sneak in? The Karate Monkey is a trail bike from cult US firm Surly. Subscribing to the brand’s usual utilitarian approach, it can be built up in multiple forms, from suspension-equipped mountain bike to monster tire-wearing haul-it-all fat bike.

Not a creature that’s worried what it eats, the Karate Monkey is a brawny machine. Even the quickest of laps around the park reveals a very aggressive and modern trail bike. But with fixings for everything, including traditional mudguards, there seems no reason not to pile it up with kit either.

On the road

Around for years, Surly’s no-nonsense bikes have built a dedicated following. However, in the UK the logistics of getting them here means they come with a higher-than-average price, which is a shame. Objectively it’s hard to recommend a bike that shares a groupset with a competitor costing almost half the price.

Still, the Karate Monkey made us smile the second we jumped on it. Despite weighing a tonne, and being a tad silly, it’s a fun machine that feels indestructible. Any steel frame is likely to last a long time, but the Surly really seems as if it will still be cranking out the miles come the end of the world.

Plus all the angles are spot-on. This particular build also comes with great wheels, and very good, if aggressive, tires. Get them setup tubeless and you’ve got a true ever-ready, do-anything bike. Combined with the 1×11 groupset, the lack of a front derailleur helps keep the whole package as stripped down as possible. The only thing that bugged us was its excruciatingly loud freewheel, although this can be swapped for a quieter-but-slower-to-engage alternative.


Super rigid across its length, sporting mammoth 800 mm wide bars, and fitted with motocross-style tires, you don’t so much carve your line with the Karate Monkey as excavate it.

With a raked-out 69° head angle, the bike is very stable, but rather than this making it sluggish to turn, it only provides a better platform from which to push it into the corners. Similarly, when heading downhill it rarely feels as if it wants to chuck you over the bars.

Despite functioning perfectly as a mountain bike, a stubby headtube and low stack height mean it’s not so upright as to be impossible to ride quickly, It’s so stable that any extra weight you add to it in the form of bike packing bags does little to knock it off kilter, even when riding more testing trails.

Although a bit overkill for more sedate gravel roads with its current tires, it could easily be tweaked for less extreme riding by chopping down the bars and swapping in slicker treads. Run either way, while unlikely to win any races, it still makes a surprisingly competent tough-condition tourer.

The spec

The frame Heavy, blue, and made of steel, the Karate Monkey’s frame deadens some chatter from the trail or road surface, but isn’t particularly springy. Unyielding enough to exhibit little flex when loaded, it’s covered in mounts for every sort of fixture and fitting.

These include points ideal for attaching the platform-style front racks increasingly popular with backpack-averse cyclo-tourists. Infinitely adaptable, there’s routing for a dropper post, a fat headtube that’ll take a suspension fork, and the ability to fit 29-inch wheels if you like.

Using bolt-through hub fixings held in place by splendidly robust stainless hardware, it’ll also accept a huge range of different hub types; a boon if you have an old pair lying around that you’d like to use for commuting.

Able to swallow 135 mm, bolt-through 142 mm, or Boost 148 mm hubs, the Karate Monkey has a fantastic solution to the irritatingly large number of axle standards available. Branded ‘gnot-boost’, the frame’s mid-size 145 mm dropouts can be pulled apart to accept 148 mm-wide Boost hubs or squished down to fit 142 mm. Want to run your old 135 mm wheels? Just bung in a spacer. It’s a stroke of low-tech cunning in an industry plagued by confusing high-tech standards.


SRAM’s simple single-ring 1×11 NX groupset perfectly suits the Karate Monkey. As do the brand’s powerful Level brakes. With almost all the features you’d expect, we can’t say the performance of either lets the bike down. However, given the price, you might reasonably have expected to find a groupset a level above the one fitted.

For example, swapping up to NX Eagle could have nabbed riders an extra gear, along with SRAM’s incredibly wide 11-50t cassette. Alternatively, an upgrade to GX would also have added even more polish along with the additional sprocket.

Frame of Surly Karate Monkey Bike

Finishing kit

The finishing kit on the Surly is of better-than-average quality. We dug the very wide and flat Gusset Slade handlebar, which helped keep the bike on a steady course when the going got choppy. The Genetic STV saddle was more divisive thanks to its minimalist cushioning it may prove too austere for more tender bottoms.

The small details aren’t overlooked, though. Hidden from view, nine times out of 10, bikes arrive with rubbish headsets, but the one fitted here should survive years of bad fitted. For example, swapping up to NX Eagle could have nabbed riders an extra gear, along with SRAM’s incredibly wide 11-50t cassette. Alternatively, an upgrade to GX would also have added even more polish along with the additional sprocket.


Halo’s Vapour 50 wheels are super broad and feature, you’ve guessed it, 50 mm wide rims. Giving a wonderfully rounded profile to the tires and helping them soak up bumps, they’re still light considering their width. Using a rear hub with an almost instantaneous 120-pointdriver, they generate and carry speed well, although the ratchet mechanism is very loud.

Taped and ready to be set up tubeless, this is definitely an option we’d pursue. The Schwalbe Nobby Nic tires fitted to them are the most aggressive of the bikes on test. A bit of a drag on anything smooth, they’re the most capable once the terrain breaks up, and they certainly don’t mind a bit of mud either!


Frame: Surly 4130 chromoly steel

Groupset: SRAM NX 11-speed

Brakes: SRAM Level hydraulic disc

Chainset: SRAM NX single-ring 32t

Cassette: SRAM GX 11-42t

Bars: Gusset Slade No Rise

Stem: Gusset Staff

Saddle: Genetic STV

Seatpost: Gusset Lofty

Wheels: Halo Vapour 50 27.5

Tires: Schwalbe Nobby Nic Addix 27.5×2.8


Size tested: MChainstays (C): 423 mm
Weight: 13.54 kgHead angle (HA): 69°
Top tube (TT): 610 mmSeat angle (SA): 73°
Seat tube (ST): 419 mmWheelbase (WB): 1103 mm
Stacks (S): 597 mmBB drop (BB): 55 mm
Reach (R): 427 mm 

Rating: 7.4/10

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