Sonder Signal need to know

• Handmade 4130 steel frame with size-specific chainstays and up-to-date trail geometry
• Cane Creek Helm air fork upgrade comes with a 35mm chassis and 130mm travel
• Full SRAM GX Eagle drivetrain, now updated with a super-wide 10-52t cassette
• Upgraded Hope Fortus wheelset adds weight but supreme durability

Steel hardtails are about more than just the retro look, the Signal mixes old-school materials with modern geometry

The Sonder Signal ST GX is a contemporary steel hardtail, by which I mean it sticks with the cosseting steel frame, and adds a host of modern touches like modern sizing and suspension… all essential if the bike’s going to cut it as one of the best hardtail mountain bikes in the business.

It also makes it perfect for a winter hack when the trails are disgusting, or as a trail bike if hardtails are your thing (and after 15 years testing them, they’re most definitely mine).

The bike on test is not an off-the-shelf build from Sonder. It uses a SRAM GX build and although my test bike’s price with upgrades is a hefty £2,899 (the Cane Creek Helm fork and Hope wheelset bumping it up significantly), the frame only option is £549 and the bike range starts with the SRAM SX Eagle model for a more reasonable £1,199.

Sonder also makes the Signal from titanium, making the bike lighter but much (much) pricier

It’s a whole load more money than the titanium version of Sonder Signal we tested in 2023.

A blend of modern geometry and sizing, quality hardware and a premium fork, all based around a very sweet looking steel frame – it’s all there.

But with so many great hardtails now made from hydroformed aluminium, is there still a place for traditional steel, besides the pride of doing things old school? There’s only one way to find out…

Tyre clearance is rated up to 2.5in, making it ideal for upspeccing to a bigger tyre for more comfort

Frame

To keep things quiet, external cable routing is a good starting point, and even though it may look dated, the Sonder has this box ticked. The routing for the rear mech and brake is direct and well managed, but it’s the cable for the dropper post – the only one concealed inside the frame – that raised some questions.

The housing for the dropper cable is piped through the down tube, exiting below the bottle cage before diving back into the seat tube – nothing unusual here. There are no rubber bungs to secure the cable in the three frame ports though, and this translates to occasional rattling when riding. It’s only noticeable when the trail turns rough and rowdy, and it’s not become an irritation, but it does feel a touch unfinished and an area for improvement.

Internal cable routing is restricted to the dropper post, but it’s unlagged and noisy

Something else that’s missing is protection for the driveside chainstay. There’s no moulded armour or rubber strip, just the bare frame. It looked naked and vulnerable, so I added some VHS 2.0 Slapper Tape to protect that sparkly copper paintwork.

Sonder’s design brief for the Signal hardtail was to make it great for big days out but also, ‘really good fun to throw around in the local woods’. Shorter chainstays were a key consideration to achieve these seemingly disparate goals. The size-specific stays on this XL measure up a tight 435mm, that’s 15mm less than the Whyte 629 – a benchmark 29in trail hardtail for me. Yes, I had initial concerns that stability may be compromised in order to retain some pop and fizz. Yet, it seems I needn’t have worried, and it has served as a reminder that digging too deep into geometry charts can often mislead you into prejudging how a bike will ride.

No steelie would be complete without gussetting and some beautiful welds

Geometry and sizing

Scan the Signal’s geometry chart and it’s plain to see that this trail hardtail is up-to-date without pushing any boundaries. At 6ft 2in, I find myself sitting at the bottom end of most brands’ height recommendations for a size XL frame. But with a shorter inseam and longer torso and arms, I’ve historically had to make compromises with this size.

The Sonder dimensions gave me no reason for concern about choosing the XL though. I measured a 64° head angle, a 483mm reach and 1,240mm wheelbase – all good numbers for this size frame – and the dropped top tube gives a usefully low standover height too. The stock 150mm stroke dropper post teamed up with the 485mm seat tube works well with my leg length.

The size XL bike comes with a 150mm dropper, which suited my small legs but is too short on a bike this size

Getting a good riding position when seated has always been a concern for me, so does the Signal work well for a long day in the saddle? The Signal’s relatively slack 74.5º effective seat tube adds welcome length to the frame, resulting in a rangy 670mm horizontal top tube. When combined with Sonder’s 780mm handlebar and short stem the result is a seated position that feels both comfortable and efficient.

Does the slacker seat angle mean a trade off when it comes to climbing efficiency? Well, the 435mm size-specific chainstays may be 15mm shorter than those on the super-long Whyte 629 but I’ve not felt unbalanced or lost traction, even on tight and technical pitches.

The Cane Creek Helm II Air is supple and comfortable, and a great upgrade for a hardtail to soften the trail

Suspension

The Cane Creek Helm II Air is an upgrade over the stock fork (now listed as a RockShox Pike Ultimate) and is a premium piece of hardware, with a price tag that’s higher than the frame alone.

Cane Creek’s 35mm chassis matches the Pike Ultimate in stature but with a listed weight at just over 2kg, it’s a shade heavier – not a real world issue for my size XL test bike with a 90kg rider on board though. Out on the trail, the Helm II fork feels like a perfect match for this steel hardtail, balancing support with small bump sensitivity and showing no quirks or issues. Once dialled-in, I’ve rarely touched the array of adjusters, with just a slight increase in the rebound speed after the initial bedding in period.

The Helm 2 proved to be fit and forget, I set the dials right and never fettled with it again

It also maintained a consistent air pressure throughout the test. In fact, it’s been a faultless performer. Yes, it’s still not enough to stop my eyeballs almost popping out on the roughest trails, and even with all the headbanging, I still can’t seem to shake the idea that this is what mountain biking is really about.

SRAM’s GX shifting holds the perfect line between crisp performance and value for money

Drivetrain

The GX Eagle is crisp under shifting, it’s lightweight and there’s a great feeling of connection to the drivetrain when you’re doing so – never vague, even if the action isn’t that light. The monster 52T cog allows Sonder to spec a 32T chainring and still give a super-low ratio for winching up the steepest climbs, with the 10T sprocket resulting in enough top end grunt for flat-out fire road descents.

I’ll admit that the big jump to SRAM’s bail out climbing gear did take some getting used to (in contrast to the top three cogs on Shimano’s more evenly spaced 12 speed cassette) but it does keep the transition between each of the other eleven gears closely spaced, which is a benefit on rolling singletrack. But, when the trail takes an unexpected upward twist, the 10T jump between the 42T cog and the 52T can make the difference between stalling out, or cleaning the climb.

My upgrades included ditching the Sonder wheelset in favour of a heavier but tougher Hope Fortus setup

Wheels and tyres

Sonder has done a decent job with its own brand Sonder Alpha 29 wheels. Wide 30mm rims, regular J-bend spokes and a pair of premium-looking hubs add up to a package that feels like a good match for the Hope hubs. I upgraded to the pricier Hope Fortus 30 hoops, which added weight but proved bombproof over 12 months of testing.

The stock 850g Schwalbe Hans Dampf tyres have a light-duty casing and more closely spaced tread than my Maxxis Assegai and Dissector control tyre pairing.

While the narrower Schwalbe tyres do a better job of cutting through the winter filth (and pick up less mud too), their 2.35in width feels a touch unforgiving when speeds increase and you’re clattering over roots and braking bumps. Even set at relatively low pressures, 23psi front and 25psi rear, the stock tyres miss the extra cushioning of the plump 2.5/2.4in Maxxis combo.

The Signal has a 160mm rotor out back, which is all that’s needed on a hardtail where speeds are usually lower than on a full-susser

Brakes

The stock SRAM G2 R four-piston brakes, although unremarkable visually, seem fit for purpose on a 130mm hardtail and have a lever profile that hits the spot for me too. I did have initial concerns though; not as much with the older international standard (IS) calliper mounts on the frame, which seem to be a common sight on steel hardtails, but more the rotor sizes that Sonder has chosen.

I weigh around 90kg when kitted out for a ride, so when I first spotted the 160mm rear rotor I immediately thought I’d be swapping it out to match the 180mm up front. And you know what? Those SRAM G2 brakes have been faultless. Sure, I’ve been mostly riding trail centres and techy forest singletrack but even with the standard organic pads I’ve had plenty of power on tap, excellent modulation and I’ve still not cooked a rotor. I stand corrected.

Sonder’s ownbrand bar and stem is a great combination, wide and stubby respectively

Components

Sonder specs its Clutch lock-on grips on the Signal ST, which use a classic diamond pattern with additional waffle squares below. The soft compound rubber feels great, with or without gloves, but they’re just too slim for my large hands, so I’ve swapped them out for a pair of Deity Knuckledusters, with an increased diameter.

Sonder’s in-house Abode saddle uses a base that’s designed to flex and work in tandem with the light foam padding and sure enough gives plenty of comfort. Its design is narrow enough to not inhibit movement fore or aft, but it’s not quite as supportive as my tried and tested option, the SDG Bel Air V3. For a stock saddle though, it’s not far off the mark and certainly a cut above many of the options which I’ve recently experienced.

The Signal is spot on for singletrack, it’s weight and good geometry make it composed and comfy

Performance

Lively, comfortable, nimble and forgiving are the key words here. The Signal ST may not have the unflappable sure-footedness of the Whyte 629 – one of my favourite hardtails – but it has bags of character and feels more involving while retaining all the qualities steel frames are renowned for.

It’s not a quiet bike though, the dropper post cable is the only one routed internally and it’s not anchored at the entry or exit points of the frame. This creates an annoying rattle, especially hitting rough, rooty tracks at speed. I added a rubber VHS Slapper chainstay protector to conserve the paint and reduce noise further.

The Signal’s geometry is good, with a low bottom bracket and raked out head angle it’s stable in the corners and more than competent when it gets steep. It’s soundly in the descending category as a hardtail though, thanks to its 14.5kg weight, which is firmly in full suspension trail bike territory.

One of the best hardtails I’ve ridden. Nuff said.