For as long as mountain bikes have had gears, most of them have shifted the same way. A derailleur hangs off the back of the frame and pushes the chain from one sprocket to the next. On electric mountain bikes, that's turning into a proper technology fight. SRAM and Shimano keep refining the derailleur, now electronic, wireless and powered by the motor's battery. Motor makers want to swallow the gears whole and let the bike shift by itself. I've been following both camps closely, and here's where I think the fight stands, and where I come down on it.
The derailleur camp: older, lighter, already automatic
The derailleur isn't standing still. SRAM's Eagle Transmission bolts straight to the frame without a hanger, and an X0 derailleur weighs about 475 g. Shimano's Di2 groups have wired e-MTB derailleurs that run off the main battery. Both brands already offer automatic shifting too, Shimano with Auto Shift and Free Shift, SRAM with Auto Shift on its Eagle Powertrain system. In our catalog, 255 of 626 eMTB builds with a rear derailleur now shift electronically. Our SRAM Transmission vs Shimano Di2 guide goes into the details.
That changes the debate. Gearboxes don't own the word "automatic". What a gearbox really changes is where the gears live: sealed inside the motor rather than hanging out under the rear axle.
The gearbox camp: motor and gears in one sealed box
Right now, four systems make up the other side.
- [Pinion MGU E1.12](https://emtbmag.com/motors/pinion-mgu). Motor and 12-speed gearbox in one unit. It shifts under load and standing still, has Pre.Select and Auto.Shift, and Pinion asks for an oil change every 10,000 km. It makes 85 Nm and 600 W and weighs 4.14 kg. You'll find it in bikes like the Simplon Rapcon :ePinion and Moustache Clutch.
- Gobao X1P eCVT. A stepless transmission with 150 Nm, 1,500 W and up to 500% range. In automatic mode you pick a cadence and the system holds it. It weighs 3.85 kg and powers the Alutech ePelmo X1P.
- Intradrive GD8. Eight speeds, 480% range, shifts in about 0.1 s and downshifts automatically. 700 W peak, 4.5 kg. The first bikes are the Obscur ENYX and the Alutech ePelmo GD8 (our story).
- Avinox MG Concept. Shown at Eurobike in June 2026 and developed with Canyon, Commencal, Forbidden and Mondraker. Avinox promises shifts in under 0.1 s, shifting under high torque and at a standstill, a cadence-based auto mode and an "AI+" auto mode. The internal unit is meant to need no maintenance in its lifetime, and it drives a single-speed chain or belt. Avinox calls it a smaller, lighter platform but hasn't published a weight.
The weight math
For me, this is where the fight gets decided. A gearbox replaces the derailleur and the cassette. On SRAM X0 Transmission that's about 475 g plus 376 g, so roughly 0.85 kg. Add that to a conventional motor and compare it with the motor-gearbox units (ignoring differences in chain, cranks and tensioner):
Drive weight: motor + derailleur vs motor-gearbox
| Drive unit | Derailleur + cassette | Total | |
|---|---|---|---|
| Avinox M2S + SRAM X0 | 2.59 kg | ≈0.85 kg | ≈3.44 kg |
| Bosch CX Gen 5 + SRAM X0 | 2.8 kg | ≈0.85 kg | ≈3.65 kg |
| Gobao X1P eCVT | 3.85 kg | none | 3.85 kg |
| Pinion MGU E1.12 | 4.14 kg | none | 4.14 kg |
| Intradrive GD8 | 4.5 kg | none | 4.5 kg |
Every motor-gearbox on sale today is still heavier than a strong conventional motor with a derailleur and cassette. Against a Bosch CX setup, the gap runs from about 0.2 kg for the Gobao to about 0.85 kg for the GD8, and against an Avinox M2S it's bigger still. On an eMTB that weighs 23 to 27 kg that may not sound like much. But the weight sits in the drive unit, on top of bikes that are already heavy. A DJI Avinox M2S weighs 2.59 kg and makes 1,500 W. The Pinion MGU weighs 4.14 kg and makes 600 W.
Where gearboxes win, and where derailleurs still do
Gearboxes have a strong case on durability. There's no derailleur to smash on a rock and no cassette to wear out, you can shift standing still before a steep ramp, and some bikes run a clean belt drive. An oil change every 10,000 km, as Pinion asks, is a very different service rhythm from swapping chains and cassettes.
Derailleurs hit back with weight, price and choice. Hundreds of eMTBs use them, every workshop can fix them, and they work with the most powerful motors on the market. The gearbox bikes I mentioned cost €11,999.95 (Alutech ePelmo X1P) or start at €12,500 (Obscur ENYX). Pinion MGU bikes in our catalog start at €5,999.
“I believe automatic shifting has its place, but only once the whole system weighs less than the motor and derailleur parts it replaces.”
Ilya Alikov, eMTB Magazine
My verdict
I'm not against automatic gearboxes. A bike that shifts by itself, never misses a gear on a technical climb and makes bent derailleurs a thing of the past is exactly what an electric mountain bike should be able to do. But I think automatic shifting only earns its place once the construction weighs less than the parts it replaces, the motor plus derailleur and cassette. None of the systems on sale gets there yet.
What I'll be watching
The Avinox MG Concept is the one that could change my mind, because Avinox has built its whole motor line around low weight. If it reaches production lighter than an M2S plus a derailleur drivetrain, the argument is over. Until then, the derailleur, automatic or not, stays the smarter choice for most riders. Gearboxes remain a fascinating option if you'd rather spend less time in the workshop than save grams.
Frequently asked questions
Can a derailleur eMTB shift automatically?
Yes. Shimano has Auto Shift and Free Shift for its Di2 e-MTB derailleurs, and SRAM has Auto Shift with Eagle Powertrain.
Do gearboxes need less maintenance?
They get rid of the derailleur and cassette, the parts that wear and break most. Pinion asks for an oil change every 10,000 km on the MGU, and Avinox says the MG Concept's internal unit needs no maintenance in its lifetime.
What is the Avinox MG Concept?
A motor with a built-in gearbox that Avinox showed at Eurobike 2026, developed with Canyon, Commencal, Forbidden and Mondraker. It promises shifts in under 0.1 s, manual and automatic modes and a single-speed chain or belt. There's no weight or launch date yet.
32 years of riding experience, from a school bike to today's high-tech e-MTBs. My goal is to build the most complete and accessible e-MTB catalog to make choosing easier, and to bring our readers the latest news.
