Genesis Tarn 20 review

Plush frame and sorted kit amplify plus-sized playfulness

Our rating 
4.5 out of 5 star rating 4.5
GBP £1,900.00 RRP | AUD $4,290.00

Our review

It’s early days for plus-sized bikes, but the responsive, playful feel and impressive handling put the Genesis up there with the best we’ve tried so far
Buy if, You want a zinger of a steel hardtail that's – at least for now – sitting at the top of the plus-sized class
Pros: Playful yet surefooted ride, lively frame, well-thought out spec
Cons: Foam grips are lame, but easily replaced
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It’s easy to assume the big, fat tyres of plus bikes dominate their ride character to the point where they all feel the same. But the more we ride the more it’s clear you can end up with very different bikes even with the same balloons wrapping the wheels.


Related: Trail Tech: Exploring 27.5+

It’s also clear that not all manufacturers have got their handling or clearances sorted to make the best of the bigger volume rubber. The good news is the Tarn is the one of the best plus hardtails we’ve ridden, and it has a great parts package for the price too.

Classy chassis

That second bit is particularly impressive, given the tapered head tube, super-sloped top tube, Boost 148x12mm rear axle frame, built from Genesis’s own double-butted Mjolnir steel tubing blend. The wide-spread rear stays provide a smoothly supple ride that really syncs well with the kind of experience you’re likely to want from a plus bike. Rather than feeling dead under power like some steel frames it’s got a really lively spring as you press on the Race Face cranks.

148x12mm ‘boost’ rear axle spacing on the genesis tarn

‘Boost’ 148x12mm rear axle spacing features out back

Despite being much heavier, the Maxxis Chronicle tyres roll really fast and, remarkably, the complete bike is lighter than both the other steel bikes we were riding alongside the Genesis (namely the Onza Jackpot and Ragley Piglet).

We rarely ran out of braking and driving grip even on the sketchiest scree sections of the surrounding wild bridleways either. Add the root- and rock-ignorant, momentum-maintaining tyre volume and the Tarn repeatedly dropped the Ragley and Onza on the rougher singletrack sections.

Properly dialled

This has actually become more significant the more we’ve ridden other plus bikes too. That’s because several of those have proved to either under- or over-steer frustratingly or just have an awkward overall balance that’s left us dabbing and cursing.

The genesis tarn, out on the trails in the english lake district

The Tarn’s personality is lively and playful – what you want from a plus bike

In contrast, the Tarn’s combination of super long stretch and 68-degree head angle made the fat front tyre feel confident yet easily responsive at all speeds. It even feels okay on the sloppy, slippery conditions that are a nightmare on most plus bikes.

The 110mm wide Boost axle of the Reba fork is further stiffened with oversized hub contact caps for rich front end feedback and the under-seat dropper lever means it’s definitely not scared of the steeps.


It’s always the sign of a good bike when we’re scratching around for something to offset all the positives with. However, the only things we didn’t like on the Tarn were the racer-style foam grips, which neither feel good nor last long. That makes them the polar opposite of the rest of this surprisingly playful, well-sorted plus-sized package.

Product Specifications


Name Tarn 20
Brand Genesis Bikes

Available Sizes S M L XL
Brake Levers Shimano BL-M506
Saddle Genesis MTB
Seat Angle 72
Seatpost KS Dropzone manual dropper 31.6mm
Shifters Shimano Deore XT SL-M8000 (R/H only)
Stem Genesis Trail, 55mm
Weight (kg) 13.67
Spoke Type 14G Stainless Silver DB w/ Brass Nipples
Rear Wheel Weight 3110
Bottom Bracket Height (in) 12.2
Chainstays (in) 17.52
Seat Tube (in) 19.02
Standover Height (in) 28.54
Top Tube (in) 25.59
Wheelbase (in) 44.88
Rims WTB Scraper i45 27.5" Sleeved
Rear Tyre Maxxis Chronicle 27.5x3.0", EXO/TR, 120TPI Folding
Bottom Bracket Raceface X-Type Team XC, 73mm
Front Hub KT Sealed Cartridge 6-Bolt
Brakes Shimano BR-M447 w/ SM-RT56 180/160mm Rotors
Cassette Shimano CS-M8000, 11-42T
Chain KMC X11
Cranks Race Face Aeffect Cinch 30T
Fork RockShox Reba RL Solo Air 120mm
Frame Material Genesis Mjölnir Seamless Double-Butted Cromoly
Front Tyre Maxxis Chronicle 27.5x3.0", EXO/TR, 120TPI Folding
Rear Hub KT Sealed Cartridge 6-Bolt
Front Wheel Weight 2470
Grips/Tape Genesis Silicon, 130mm
Handlebar Genesis Flattop, 740mm
Head Angle 68
Headset Type FSA
Rear Derailleur Shimano Deore XT RD-M8000-GS
Frame size tested L