The Sonder Transmitter, from top value UK outdoor brand Alpkit, has been one of my favourite rides for a while now. And with news of a carbon version, I've been waiting impatiently for an exclusive test sample — so does it live up to expectations?
- SRAM 12-speed: XX1 and X01 Eagle
- Skinny full-sus or plus hardtail for the UK National Endurance Champs?
Sonder Transmitter Carbon spec overview
- Frame: Carbon fibre
- Fork: Fox 32 Float FIT4 Adj Boost 120mm, travel 100mm
- Wheel size: 27.5+ / 29”
- Drivetrain: SRAM XX1 Eagle 32x10-50t
- Brakes: SRAM Level Ultimate 180/160mm
- Head angle: 65 degrees
- Seat angle: 73 degrees
- Reach: 50mm
- Weight: 11.1kg size large
Sonder Transmitter Carbon frame and kit
We built our sample bike up from a bare frame, which let me appreciate some of the detail that you won’t immediately notice if you go for one of the five complete bike options (from NX1/Sektor at £1,499 to XX1 Eagle/Pike at £3199).
The most obvious is that the internal gear cable routing isn’t just a set of holes that you need to try to coax cable between. Instead, there are full-length pipes bonded inside the frame that you can just slide the outer through all the way.
With only the chainstay section of the rear brake and the bridging section of the dropper post cable between the seat tube and down tube exposed, the frame looks clean and everything is tucked away from potential damage.
The bottom bracket is threaded for external bearings, avoiding all the short life, creak and other issues associated with press fit systems. The seat post bore and internal headset are a clean, precise fit and the 148×12mm Boost rear axle slots securely and neatly into the fully replaceable driveside dropout.
The chainstays also drop down low before heading to the bottom bracket, which reduces chain slap and noise. Tube profiling is pretty extreme elsewhere too, with the same flat ovalised top tube form as the alloy bike extending back around the short seat tube into widely spaced narrow diameter seatstays.
Having the bare frame also let me get an accurate frame weight of 1,130g for my large sample, which means a saving of 700g over the alloy Transmitter chassis and significantly more compared to most steel hardcore hardtail frames.
It’s also only 100–200g heavier than the lightest XC race hardtails. That translates to a build that’s just a hair over 10kg with carbon 29er wheels and Onza Canis 2.25in tyres on for racing and could go well under that with a narrower bar and conventional seatpost rather than the Bontrager Drop Line dropper post I’ve plugged in.
Racey weight, rowdy character
As much as it can be a competitive XC machine (I clocked my fastest four laps ever round the Dalby World Cup course on it) that’s definitely not playing to the true potential of the Transmitter. That’s because Sonder has taken the super slack 65-degree head tube of the alloy bike and extended the reach slightly (a large is now 450mm).
It’s also shortened the seat tube for a lower centre of gravity and to let you size up if you’d normally be a medium without compromising standover or having to use a stubby dropper seatpost. The result is a proper aggro attack bike that loves to shove its big front tyre into trouble and then boss it out big style.
It’s a natural weight-back, front-wheel-up lip launcher and drop sender too. Because the 120–130mm travel fork parameters aren’t excessively long, the geometry doesn’t change dramatically when you’re hard on the brakes or G-ing out through a berm. It also means that front wheel impacts aren’t completely hidden so that you’re naturally ready for them to come through the back wheel a split second later.
If you get the pressures right, extra tyre volume at either end takes out some of the impact sting and delivers a double win of increased traction and smoother momentum over roots and rocks that would shake conventional 27.5in wheels to a standstill. Low weight and impressive stiffness through the short 425mm chainstays mean it charges out of corners too.
Despite the skinny seatstays and flat top tube the handling precision and drive punch do come at the price of a firmer ride feel compared to the alloy bike. Tyre clearances are also very tight at the rear end, with 27.5×2.8in rubber grazing close to the chainstays and 29×2.25in tyres skimming the seat tube, so there’s little scope for adding bigger, softer boots.
The way that radical head angle wanders around at slow speeds on climbs won’t agree with more traditional handling fans either.
But if you’re after a responsive, race shocked ‘rally’ ride feel with superb corner scything, tech dominating handling, raceable weight, extra plus tyre traction and user friendly build features, it’s a proper stand out and a total bargain to boot.
Sonder Transmitter Carbon early verdict
Blisteringly fast, sweetly detailed, radically dialled and still a total bargain.
This article was originally published in What Mountain Bike magazine.