Calibre Bossnut review: a bargain buy with the performance potential to slay £4,000 bikes

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Calibre’s latest Bossnut is proof that impressive MTB performance needn’t cost the earth, retailing for an affordable £1,499.

Sorted geometry and a thoughtful spec combine for commendable on-trail manners, but it’s the bike’s potential that really impresses.

A few choice upgrades, such as tyres and a new fork, would put the Bossnut on a level footing with much costlier rigs, cementing it as a genre-defining trail bike.

Without those upgrades, it’s more suited to the pace and skills of beginner riders on tamer terrain, so save some cash for new parts if you want to unleash its full potential.

Calibre Bossnut frame and suspension

Built from 6061 aluminium, the Bossnut’s frame uses hydroformed tubes, creating sleek lines that are more befitting of a higher price tag.

Within the front triangle, there are two accessory mounts and a single bottle mount. Cables are routed externally, fixed in place with their own bosses and clamps rather than cable ties.

The Bossnut has Boost 148 rear-axle spacing, is made for 29in wheels only – although the extra-small size runs 27.5in wheels – and has a standard tapered head tube.

However, it misses out on SRAM’s Universal Derailleur Hanger, limiting you to Calibre’s bespoke hanger rather than SRAM’s widely available universal model.

Suspension

Using a linkage-driven single-pivot suspension design, the Bossnut has 135mm of rear-wheel travel.

Here, a yoke and linkage drive the shock to adapt its leverage rate, with the aim of providing good small-bump sensitivity and plenty of ramp-up.

Calibre Bossnut geometry

Nestled firmly within the trail bike category, the Bossnut’s figures are proof that decent geometry needn’t cost the earth.

Up-front, each of the five frame sizes (XS to XL) has a 64.5-degree head angle. This is matched with an effective 78-degree seat tube angle.

Bar the XS frame – which has 425mm chainstays – all the other sizes have a balanced 445mm chainstay figure. Reach figures span from 420mm, hence the shorter stays on the XS, up to 500mm for the XL.

Sitting at 337mm, the BB is low, while the 1,250mm wheelbase is generous.

The Calibre’s geometry figures signal rowdy intent, and I approve.

Calibre Bossnut specifications

There’s plenty of beauty in the Bossnut’s spec. It has big-name parts where they matter and unbranded ones where they don’t.

Damper duties are taken care of by RockShox, with a 140mm Recon Silver RL fork and a Deluxe Select R shock. Shimano supplies its CUES drivetrain with a 10-speed, 11-48t cassette and 32t ring.

Shimano’s non-series MT401/410 brakes are fitted and clamp 180mm discs.

Maxxis tyres – albeit the dual-compound versions – are fitted front and rear, with a Minion DHF and Dissector combination.

This culminates in a 16.71kg size-large build.

Setup

Given the simplicity of the Bossnut’s fork and shock, getting it ready to ride was straightforward. I inflated the rear shock to 165psi – giving 28 per cent sag – and fully opened the rebound adjuster.

At the fork, I inflated this to the recommended 100psi and fully opened the rebound adjuster. I left the fork’s threshold compression adjuster fully open.

This setup felt balanced, so I left it unchanged for the duration of the test period.

Calibre Bossnut climbing performance

Despite the on-paper 78-degree seat tube angle, it felt slack enough at full mast that I had to angle the saddle nose-down and push it as far forward in the rails as possible.

Once set like this, however, the bike’s geometry balances your body’s weight out, even on steeper 15 per cent gradient ascents.

That’s fortunate because to keep consistent traction at the rear for drive and the front for control isn’t an intricate jamboree of consistent and tiring weight shifts.

If, like me, these types of climbs are your bread and butter, you’re going to appreciate the Bossnut’s feel.

Sit back and relax

Cast your gaze downwards when you’re seated and you’ll be pleased to see you’re sitting atop the cranks and bottom bracket rather than behind them.

This boosts comfort and efficiency convincingly – your piston-like legs work vertically beneath your hips rather than stretched out in front of you, to create directly efficient drive.

But it also gives the Calibre a relaxed climbing posture, where cruising about rather than burying yourself and blowing up is the preferred option.

Longer ascents and all-day epics are easily conquered when your body is in this this straight-back, relaxed position.

The long chainstays improve this further, centralising your weight between the wheels better than bikes with shorter back ends.

Weight shifts have a lesser effect on back-wheel grip and front-end steering accuracy, which is great for helping to hide any destabilising mistakes you make.

The Bossnut's calm, relaxed feel is well partnered with the hefty 16.71kg weight figure. This makes it well suited to a wide range of riders, but the fittest people may get frustrated by its lethargic progress.

Cueing up problems

The 11-48t cassette and 32t chainring limit the bike's climbing pace.

While having 10 ratios never left me short-changed or hunting for an unobtainable cadence, the lowest gear couldn’t provide enough mechanical advantage to winch comfortably up the steepest climbs.

Grinding rather than spinning, I was continually pressing the shifter to select an extra, imaginary lower gear.

Depending on the terrain, beginners or riders with lower fitness levers are probably going to want a lower gear, suggesting a drivetrain upgrade – whether that’s a smaller chainring or lower biggest cassette sprocket – is on the cards.

Arguably, however, Calibre should have specced a smaller 30t chainring with the CUES cranks in the first place.

Suspension smoothness when rumbling along a man-made trail or fireroad, especially from the fork, is good.

The basic Recon dips in and out of its sag point resplendently, ironing out buzz-inducing vibrations well.

The rear end doesn't quite match this performance; it’s more inert than fluttery. This is great for helping to translate rider effort into forward motion rather than suspension bob, but not so good for traction or comfort.

Calibre Bossnut descending performance

A dropper is commendable at this price point – and it's a long-travel one at that. The light thumb lever and smooth action add to the premium feel on what is a budget mountain bike.

Not having to manually adjust your seatpost is a luxury riders of more expensive bikes take for granted, and now those who own a Bossnut will, too.

Starting down the trail reveals the Bossnut’s stance is aggressive and ready for action.

The long, slack and low figures (445mm stays, 64.5 head angle, 337mm BB) mould your body into the bike, sitting comfortably behind the handlebars rather than perching perilously on top of them.

Those numbers also slow its handling down, adding a welcome dose of lethargy to the short travel bike’s character.

This makes it easier to keep on track, heading down your chosen line. The bike works as a two-way filter, keeping rowdiness from the trail affecting the rider, and mistakes made by the rider from affecting the bike’s trajectory on the trail.

Your weight is distributed neutrally between the front and rear wheels; you don’t have to work hard to keep it on track.

Inspiring reams of confidence, it proves that sporty, capable performance from the chassis needn’t cost an arm and leg.

There’s always a trade-off

But there are several unintended consequences to having all this performance well within your reach.

Push the fork harder than just cruising – where it feels impressively supple and smooth – and a ride-disrupting compression spike is instantly apparent.

Mashing your way down a ferociously bumpy trail is an alarmingly harsh process; the fork’s unable to move quickly enough to absorb bumps proficiently.

All that impact force gets shot like lightning bolts through your hands and arms, causing you to take consistent compensatory measures. Cycling in and out of flexion, your arms will become tired and hands weak on longer descents.

Unfortunately, the excessively spikey high-speed compression is matched with lacklustre low-speed damping.

Control-inducing weight shifts – that happen intuitively a lot of the time – cause the fork to oscillate freely in and out of its travel, upsetting the bike’s sorted geometry.

Load up the front wheel for more grip in a turn, and instead of the fork resisting your body’s weight, it gobbles up travel. This unnecessarily steepens the bike’s head angle and speeds up handling just when you want it to remain calm and composed.

Turn the dial back

Keep the terrain you’re riding closer to moderate rather than severe and there’s plenty in the Bossnut’s tank.

Speed comes easily from the fast-rolling Maxxis tyres, which also hold their pace well. Just make sure you keep the dual-compound rubber well away from any glossy, shiny roots or rocks because they will skid uncontrollably across them rather than sticking surefootedly.

Lowering pressures helps, but the light rear tyre suffers from carcass flex and punctures as a result.

Its supportive rather than plush suspension kinematics seems to double any of your inputted energy; pump a compression or push into a take-off and you’re rewarded with acceleration and airtime.

Laps of your nearest jump-infested flowline will make the Bossnut feel alive.

Battling tech

But, as a package, it struggles to help you battle the wildest tech.

The suspension’s great for popping, but as a result isn’t the smoothest. It’s far from bad, but isn’t a cure-all panacea for reckless riding and making mistakes on the spiciest terrain.

There isn't the get-out-of-jail-free card that some 130mm-travel bikes with similar figures offer – the Bossnut can’t bail you out.

Component limitations

Beyond the fork and tyres, the brakes and wheels also put a dampener on the fun.

Feeling wooden and lacking power, the non-series Shimano brakes struggled to slow me down when riding determinedly on steeper tracks. While there’s a solid initial bite, squeezing the lever harder doesn’t increase power.

Arguably, sintered brake pads – which will also require a rotor upgrade – would help, but there’s no denying the MT410s aren’t the best.

Halfway through the second ride, every spoke in the rear wheel came loose, to the point where it was unrideable.

While I admit this could be a one-off occurrence, it serves as a warning that when buying a budget bike you need to keep on top of maintenance.

If I’d have continued to ride the bike without tightening any of the spokes, I would have caused irreparable damage.

You can’t say I didn’t warn you.

Calibre Bossnut bottom line

The Bossnut has the performance potential of bikes that cost more than four times as much as its reasonable £1,499 asking price.

Its geometry is the main ingredient in just how far it can be pushed.

Beginners are going to fall in love with its easy-riding performance, but only if they stick to relatively tame terrain. Here, just a mere chainring swap should do the trick to lower the easiest gear ratio and make it fun to ride both up and down.

But if you’re going to be pushing the Bossnut up to its potential with its stock parts, you’re going to be fighting a losing battle.

Wide-ranging upgrades including the fork, tyres, brakes and drivetrain will need to be considered, after which, would you have been better off buying a different bike?

The answer to that question will vary depending on your personal needs, so should you buy the Bossnut? For £1,499, yes absolutely. It’s got the potential to grow with your skills, but it’s far from perfect.

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