With weight claims of just 15.3kg, the new Rotwild dials its internal battery capacity back to just 250Wh for lighter handling and limits its standard power output to just 200W of pedal-assist for a smoother feel. But, it also adds a unique Zirbel twist remote to boost you up to 300W with its thumb-activated turbo mode…
2023 Rotwild R.X275 ultralight trail eMTB
c. Mountain Bike Connection Winter, photos by Rupert Fowler
Rotwild describes their new ultralight in-betweener R.X275 ebike as “neither bio-bike nor eMTB”. Instead, it’s an ebike developed for a more active, more sportive mountain biker who is looking to extend how far they can ride or how fast they can climb – without sacrificing the more traditional handling and feel of a regular trail mountain bike.
Rotwild says, “the R.X275 provides subtle support without imposing itself or demanding control“.
What’s new?
Then, Rotwild’s secret trick is the turbo Boost Button. Adapting Zirbel’s twister electronic shift switch, Rotwild repurposes it as a thumbs switch to get a 30-second long max power 300W boost out of the R.X275’s TQ powertrain. The TQ HPR50 motor has a max sustained power output of 250W just like pretty much every current pedal-assist motor. But for a short burst, you can get an extra 50W and double your input at the pedals. So Rotwild figured, why not give their lightweight trail ebike a turbo boost switch to give you easy-to-use control over that peak power?
The standard Rotwild R.X275 setting of the TQ system are all preset for fast pedal response yet are quite low-powered – 60W, 130W & 170W – but you always have direct access to that short 300W burst via the Boost Button in any mode. While you can’t set any of the three modes above the 200W limit, you can increase the Assist ratio if you want the motor to match your power output, and you can decrease the Pedal Response speed if you prefer a slower, smoother ramp up of the pedal-assist (like I do.)
Tech details
At the heart of the 29er Rotwild R.X275 is a 2350g (size M) full carbon frame constructed of hi-mod fibers (claimed 1893g raw without hardware). Paired with 130mm forks, the new light ebike gets 120mm of single-pivot rear wheel travel in a modern suspension design utilizing flexing seatstays and a short linkage drive shock, plus conventional internal cable routing, a UDH & 2 sets of bottle cage mounts. The Boost frame also gets a flat mount 160 rear disc brake, integrated chainstay protector, chainguide mount, the speed sensor for the TQ motor integrated into the rear dropout, and 2.4″ tire clearance.
The max 50Nm harmonic pin ring TQ HPR50 motor drives the ebike as quietly and as smoothly as ever, with its unique degree of user customization potential – power, assist ratio & pedal response speed. In addition to the Zirbel Boost Button, Rotwild also developed their own battery in-house 250Wh battery that tucks neatly inside the almost conventionally-sized carbon downtube.
The unobtrusive TQ display on top of the downtube shows your choice of key data streams (battery status, distance traveled, range remaining, power output, etc.) plus the dot & ring indicating your support level. That single bottom on the display also cycles through the 3 pedal-assist modes plus the support-off mode.
That’s one of my pet peeves, that half the time you have to go through ‘Off’ mode to go all the way through the pedal-assist modes to the one you want. But really on the R.X275, you set the mode you want at the start of your ride, and use the Boost switch when you want some extra power. You can also sync with the great TQ App on your smartphone over Bluetooth.
Geometry-wise, the Rotwild R.X275’s head angle is slack-enough for modern trail with a steep-enough seat angle. But while its chainstays are super short for an ebike at just 437mm, it does get a pretty long front end that shifts the rider’s weight forward for better grip & control on the front wheel.
All-in, total complete weight for the top-spec Rotwild R.X275 Ultra ebike is claimed at just 15.3kg (size M).
Is it really that light?
There’s no getting around the fact that the Rotwild R.X275 feels really light for an ebike. It actually feels pretty light for any mountain bike, really. It’s just 1kg heavier than the carbon trail bike I rode at home last weekend, and a full 1kg lighter than my own carbon enduro bike.
Coming in 500g grams lighter and several thousand euros cheaper than the other TQ-powered light trail ebike I tested at the end of 2023 on the same trails in Tuscany, it also almost sounds like a good value (if you don’t look too hard at how many zeros are in the pricetag).
The large-sized R.X275 Ultra ebike I rode weighed a real 15.86kg complete with crankbrothers Candy pedals and two Fidlock twist bottle mounts (an extra 380g, bringing this large bike down to a real 15.48kg with sealant in the tires). Interestingly, that’s more than 1/2kg lighter than the 16,000€ Scott Lumen eRide 900 SL with ultra-premium Silverton SL wheels that I rode earlier this winter. I didn’t get a chance to weigh the Pro model, but the weight difference on the trail was imperceptible.
Riding Impressions
The interesting thing about fighting to make lighter e-mountainbikes, is that the solution usually boils down to giving them more compact motors with lower peak torque, and smaller capacity batteries. That typically has the knock-on effect of not only making them lighter overall, but also making the light ebikes feel more like you are riding a regular bike, AND also making them easier to pedal once that small battery runs out. Lightweight eMTBs are effectively devolving back in the direction of regular bikes you have to pedal all the time – with only a bit of extra boost they save for the bigger climbs. And I feel like that’s the kind of eMTB I can really get behind.
Riding the new Rotwild R.X275 Ultra on tight trails just reinforces how great and tunable the TQ drive system is. The smooth transition on and off power really make it feel like you are just having a strong day on the bike.
I will say that at first, I questioned why Rotwild limited the standard pedal-assist power modes to 200W, and wanted to play around with the TQ app to customize my settings more. But I quickly got used to the R.X275’s boost switch, bumping up to a peak of 300W with my thumb on the lever. I realized that on the TQ-powered Lumen I switched back and forth a lot between a middle mode for regular riding and a faster, higher-powered mode for steep climbs. But with Rotwild’s boost switch, I could leave it in an ever lower-powered middle mode for most of my regular riding, and always have max power instantly available at my finger tip.
Admittedly, having another remote on the handlebar took some getting used to (as did the standard TQ thumb switch). On my first two rides, I mixed up the dropper & turbo remotes a couple of times, but did settle in by the end of that second ride. It’s a new coordination effort to hold down the turbo switch as long as you want the max support (up to 30 seconds), but it really only happens on steep climbs, so it wasn’t that hard to acclimate.
As for support range, the 250Wh internal battery is small, and I expect you’ll likely get just about 50km/30mi out of a single charge in a mid-level assist mode. Going full gas will burn through the juice even quicker. That said, once you run out of power, it really just feels like you are riding a regular bike again, and not an especially heavy one, either.
But keep in mind, if you really have range anxiety, it’s always possible to add on TQ’s 160Wh range extender external bottle battery (an extra 1.14kg). And Rotwild even has a quick connect Fidlock mount for it so you can carry the extra battery and a full-size water bottle, too.
2023 Rotwild R.X275 – Pricing & availability
The superlight ebike I weighed was the top-tier Rotwild R.X275 Ultra with Fox Factory suspension & Transfer SL dropper, a Shimano XTR groupset, 1-peice integrated carbon cockpit, and ebike-specific 30mm internal DT Swiss HXC 1501 LS carbon wheels for a price of 12,500€.
A ‘more affordable option is the 9500€ Rotwild R.X275 Pro with Performance/Performance Elite suspension, a Shimano XT group, and alloy DT XC 1700 LS eMTB wheels.
Both new ultralight ebikes are available now from your local Rotwild dealer in four stock frame sizes (S-XL).
Also, those prices and specs align pretty closely with Rotwild’s stealthy longer travel and heavier 20kg R.X375 powered by a Shimano EP8 motor & huge 720Wh battery, meaning they can kit you out with a top-shelf eMTB for any occasion.