Sonder offers a wide range of hardtail mountain bikes, from gravel-friendly expedition bikes, through to traditional cross-country bikes and slacked-out ‘all-mountain’ models. The Frontier sits somewhere in the middle, targeting ‘multi-activity’ use – everything from trail centres and bridleways to adventure riding.

Sonder Frontier NX Eagle frame details

The hourglass-shaped head tube meets Sonder’s own 780mm Aspect bar. The Frontier’s aluminium frame looks a little old-fashioned, with its high top tube, short reach (just 440mm on the large size I tested) and mid-length 445mm chainstays. Its geometry is designed around a 100mm-travel suspension fork, or a rigid one with the same axle-to-crown measurement. The bottom bracket shell is slightly higher than on most hardtails, for extra ground clearance, while the bearings themselves are housed in a practical threaded (rather than press-fit) bottom bracket, which shouldn’t creak and will be easier to fix or replace. Up front is an hourglass-shaped head tube, while the seatstays curve down to forged drop-outs for a bolt-through axle.

The latest 148mm Boost spacing spreads the hub flanges further apart for a stronger wheel. There’s clearance for a fat 27.5x3in, or chunky 29×2.5in rear tyre. Triple bottle mounts will hold enough fluids for out-there rides. There are eyelets for a mudguard or (if you fit a seat clamp with integrated mounts) a luggage rack, hinting at a frame that could turn to bikepacking or commuting bike duties. The gear cable and rear brake hose are routed internally, and there’s a port in case you want to upgrade to a dropper post in future.

Sonder Frontier NX Eagle kit details

This build is based around SRAM’s NX Eagle drivetrain, which boasts a big 50t cassette sprocket for easier climbing. NX is close to feeling as solid and smooth as pricier SRAM mountain bike groupsets these days, with its stiffer DUB axle and crisper shifting. The SRAM Guide T brakes will be powerful enough for most, even with a smaller 160mm rear rotor. There’s no dropper post, but the own-brand rigid post is well-finished, as are the stubby stem and wide bar, which sharpen up the steering. Sonder’s Nova wheels seem tough, but feel a little lethargic when accelerating, and are heavy. Quality WTB Ranger tyres in a 29×2.4in width provide decent cushioning and roll well, but the tread pattern and harder rubber aren’t that good under braking or in the wet.

Sonder Frontier NX Eagle geometry

Sonder Frontier NX Eagle ride impressions

The Frontier felt less assured than rival bikes over small jumps. This bike gets about efficiently, with nimble handling that makes it easy to thread along twisty trails and through tight gaps. With its stubby stem and relatively steep 68-degree head angle, it has a quick steering response, so you can pick precise lines at slower speeds up steeper climbs. On flatter terrain, the geometry puts you in a comfortable, upright pedalling position.

The frame feels stiffer and more direct than the smoother and better-damped GT Zaskar LT Elite I’ve also tested recently, but lacks the punchy surge of the Kona Kahuna, also tested alongside the Sonder and GT, under acceleration or uphill. One reason for this could be the heavier wheels ‘winding up’ under load; it appears some energy is lost through the spokes and there’s a big lag in freewheel engagement when stomping on the pedals.

WTB’s fast-rolling Ranger tyres help maintain speed. Once up to speed, it’s easy to maintain pace on the Sonder, with the WTB Ranger tyres rolling fast, especially on gravel roads and trail-centre loops. However, for more aggressive mountain biking, the Frontier wouldn’t be my first choice. The Guide T brakes are dialled and the air-sprung RockShox Recon Silver RL fork irons out bumps effectively, but the Sonder transmits more feedback and trail vibrations to your hands and feet than rival bikes when the going gets rougher. At higher speeds, it feels a bit nervous, with a taller ride position and less assured feel than its rivals, particularly when faced with bigger trail features and small jumps.

It has the same fork as the Kona Kahuna, and I had issues on that bike with it bottoming-out. I didn’t have the same problem here, because I wasn’t prepared to ‘open the throttle’ on the Frontier to the same extent. That was, in part, due to the seat tube bottle mount restricting how far you can lower the saddle, but mainly because it doesn’t inspire confidence in even slightly technical terrain. This isn’t the Frontier’s specialisation, obviously, but the choppier ride won’t best suit bumpy adventures, either.

Sonder Frontier NX Eagle bottom line

The Sonder Frontier is a responsive hardtail well-suited to tame trail centre loops or cross-country expeditions across a variety of terrain, while the frame has some versatility built-in through the addition of mudguard and rack mounts. However, if you’re after a hardtail for more aggressive riding, the position and stiff frame mean there are better options to letting loose.