Auto Shift E-Bikes and Gearboxes: SRAM Powertrain, Shimano, Avinox Smooth Shift and Pinion MGU

Auto shift means the bike changes gear for you. SRAM's Eagle Powertrain does it with Auto Shift, Shimano does it on its 11-speed Linkglide Di2 kit, and on SRAM's Eagle Transmission a DJI Avinox motor can finish a shift for you. Then there's the gearbox: Pinion's MGU puts twelve gears inside the drive unit and usually runs a belt instead of a chain.

I ride a Mondraker Zendit with DJI Avinox and SRAM's X0 Eagle Transmission, and I've done nearly 1,000 miles on it. Before that I rode a Specialized Kenevo SL for five years. So here's what each maker says its system does, and what living with electronic shifting and a big motor is like on Forest trails, including what it does to chains and cassettes.

What electronic shifting feels like on the trail

"SRAM's auto shift is a game changer. I think gearboxes coming out will be another game changer and a huge technology shift, but currently the AXS system is amazing."

An e-MTB changes pace all the time. A steep kick, a flat stretch of fire road, a drop into a corner and straight back up the other side. On a big motor those changes come quicker than they ever did on a normal bike, and every one of them wants a different gear.

"It rides kind of like a motorbike with a quick shifter: as you drop into corners and hit quick climbs, the gears spin up and change for you."

Self-shuttling, which is what I love to do, is a good example: ride a downhill run at the Cycle Centre, then climb the push-up track and go again, as my downhill and uplift guide explains. That's a hard change of pace at the bottom of every run, many times a day.

The names get muddled on the trail, though. "Auto shift", "free shift", "smooth shift" and "coast shift" all mean slightly different things, and each depends on a particular motor and groupset. So here's what each maker says its system does.

Auto Shift, Free Shift, Smooth Shift: what each one does

System	What it does	What it needs
SRAM Auto Shift	Picks your gear from riding and pedal speed; override any time	SRAM Eagle Powertrain with Eagle Transmission
SRAM Coast Shift	Changes gear while you coast	SRAM Eagle Powertrain
Shimano Free Shift	Changes gear without pedalling	Deore XT Di2 with Shimano EP motors, including EP801 and EP6
Shimano Auto Shift	Predictive changes from speed and cadence, with manual override	Di2 on 11-speed Linkglide only (not 12-speed Hyperglide)
DJI Avinox Smooth Shift	The motor turns the cassette to finish a shift; shifts while coasting	Avinox with SRAM Eagle Transmission, derailleur powered by the AXS cable, switched on in the display
Pinion MGU E1.12	Twelve gears in the drive unit, 600% range, shifts while stationary	A bike built around the MGU, usually with a belt

SRAM Eagle Powertrain: Auto Shift and Coast Shift

Eagle Powertrain is SRAM's e-MTB system. BikeRadar's launch report from September 2023 says the drive unit is made by Brose and peaks at 90 Nm and 680 W.

Auto Shift watches your riding and pedal speed and shifts the Eagle Transmission derailleur for you, "so you're always in the right gear", in SRAM's words. BikeRadar explains that it uses speed and cadence sensors to choose a gear for your pedalling rhythm, however many watts you or the motor are putting out. You're never locked out: shift by hand whenever you like, and Auto Shift takes over again after 7 seconds.

Coast Shift lets the chainring turn independently of the cranks, so the bike can change gear while you're coasting. On a descent that means you can arrive at the bottom already in the gear for the climb out.

Shimano Free Shift and Auto Shift

Shimano splits it in two. Free Shift lets you change gear without pedalling, and works with Deore XT Di2 and Shimano's EP motors, including the EP801 and EP6 (The Loam Wolf). Auto Shift with Manual Override uses Shimano's Linkglide drivetrain with Di2 to make predictive gear changes from your speed and cadence.

The catch is compatibility. BIKE Magazin's test found Auto Shift only works with the 11-speed Linkglide parts. Put XT Di2 on a 12-speed Hyperglide drivetrain and you get Free Shift only. So if automatic shifting is why you're buying a Shimano bike, check which drivetrain it comes with. For scale, MBR lists the EP801 at 85 Nm and 600 W peak.

DJI Avinox Smooth Shift with SRAM Transmission

Avinox's Smooth Shift is about finishing a shift cleanly. If the bike has SRAM Eagle Transmission, DJI's FAQ says the drive unit will rotate the cassette to complete the shift when it detects a gear change. For that to work, the rear derailleur has to be powered through the SRAM AXS power cable, and Smooth Shift has to be switched on in the control display. Cycling Electric reported in May 2025 that it lets you shift while coasting, and that the motor briefly reduces its torque during a shift to protect the chain.

That last part matters more than it sounds. The Avinox M2S gives up to 150 Nm in Boost (ebike-mtb.com), and easing off for the moment of a shift is kind to a chain carrying that much. Bosch thinks along the same lines: BIKE Magazin reports that it limits the 120 Nm of its CX and CX-R motors to torque peaks partly to protect the drivetrain. My Avinox settings guide covers the modes, Boost and the Avinox Ride app.

Gearboxes: why the Pinion MGU could be next

Take Pinion's MGU E1.12. In ebike-mtb.com's 2026 test it has twelve gears and a 600% range, where a conventional drivetrain is typically around 520%. Pinion's own claim is that the gearbox needs only an oil change every 10,000 km (about 6,200 miles) and no other servicing in between. It can shift while you're stationary, too, which is handy when you've stalled on a steep, rooty climb and need an easier gear to get going again.

It's usually paired with a Gates Carbon Drive belt, which takes the chain off the list of wear parts. For a Forest rider, that's the appeal: no cassette grinding away in winter mud, and no derailleur hanging off the back of the bike.

The same test is honest about the downsides:

• Weight. ebike-mtb lists the MGU at 4.14 kg, against 2.63 kg for the Avinox M2S in its own test. It isn't quite like for like, because the MGU's figure includes its gears.
• Torque. 85 Nm and 600 W, against 150 Nm for the M2S in Boost.
• Traction. Under full load, the rear wheel tended to spin out quickly, especially on technical climbs. For what it's worth, my Avinox doesn't wheelspin: it manages that really well.
• The belt. It's low-maintenance, but if it snaps, fitting a new one is noticeably more involved than fitting a chain. The tensioner is bulky and sits in an exposed spot.

I wouldn't buy another bike with less than 150 Nm of torque, and the MGU in that test makes 85. My full power vs lightweight guide explains why I feel that strongly. But if you ride all winter and hate replacing drivetrain parts, a gearbox is worth a proper look.

What a Forest winter does to a derailleur drivetrain

The Forest of Dean in winter is wet and muddy, and in places it's clay. A derailleur drivetrain is out in all of it: the chain and cassette sit right in the spray off the back wheel, and wet riding wears them out far faster than dry. The numbers are in the next section.

Washing matters, but do it gently. Bosch says never to use a steam cleaner or high-pressure cleaner on an eBike, because water can get into the motor, hub and rear-frame bearings. DJI's Avinox manual says never to use a high-pressure spray on the motor, battery or any electrical components. My e-bike cleaning guide goes through it step by step.

All that torque eats chains and cassettes

"Avinox absolutely kills cassettes. I've been through a chain in 200 miles and a cassette in 700 miles. Bear that in mind, but it's a small price to pay for the smile on your face."

Here's how that compares with the starting estimates in the Plus1 Garage, for an e-bike on drip lube:

Part	Starting estimate, mixed UK riding	Starting estimate, mostly wet	My Avinox bike
Chain	540 miles	about 300 miles	200 miles
Cassette	1,620 miles	about 890 miles	700 miles

The Garage starts from the part makers' intervals, gives an e-bike 60% of a normal bike's drivetrain life, then takes 55% of that for a rider who's mostly out in the wet. My numbers come in under even the wet estimates, on a 150 Nm bike that I love to self-shuttle. That's exactly why every number in it is a best guess you can correct: if a part is still fine when it says it's due, tell it, and if one wears out early, set where it is in its life. Type the miles off your display now and then and it reminds you on the day something's due.

The chain is the part to watch. Park Tool's table puts the replacement point at 0.5% wear for an 11-speed or bigger cassette, and it warns that running a chain past its limit wears out the cogs and chainrings too, and a cassette costs far more than a chain. My chain wear guide shows how to measure one.

Which should you go for?

Each of these depends on the motor and groupset, so the motor on the bike you buy decides which you can have.

• You want the gear chosen for you: SRAM Eagle Powertrain with Auto Shift, or Shimano's Auto Shift with Di2 on 11-speed Linkglide.
• You want the most torque here and electronic shifting: Avinox (150 Nm in Boost on the M2S) with SRAM Eagle Transmission, which is what I ride. With Smooth Shift switched on, the motor finishes your shifts for you.
• You ride all winter and want the fewest wear parts: a gearbox such as the Pinion MGU, if you can live with the weight, 85 Nm and a belt.

For me, today, it's a big motor and AXS, and the chains and cassettes are a small price to pay. But I think gearboxes will be the next game changer.