Are Motor-Gearbox Units the Next E-Bike Drivetrain?

The conventional e-bike drivetrain still looks familiar: a mid-drive motor turns a chain, which runs through an exposed rear derailleur and cassette. That architecture works well, but high motor torque makes its weaknesses increasingly obvious. Chains wear, derailleurs are vulnerable to impacts, shifting under load can be harsh, and the rear wheel carries a growing collection of precision components.

Motor-gearbox units, or MGUs, offer a different answer: move the transmission into the motor area and reduce the rear drivetrain to a simple chain or belt.

Pinion already sells this concept in production. Avinox used Eurobike 2026 to preview its own MG Concept. Together, they suggest that integrated transmissions are moving from niche engineering into a serious alternative for premium e-bikes.

What is an MGU?

An MGU combines two functions that are traditionally separate:

1. electric motor;
2. multi-speed bicycle transmission.

Instead of sending motor and rider power through a rear cassette and derailleur, the gear changes happen inside a sealed unit near the crank.

The rear wheel can then use a simple sprocket, often with a belt-drive option.

Pinion proves the architecture can work in production

Pinion’s current E-Drive system offers 9-speed and 12-speed Motor.Gearbox.Units. The company lists:¹

Specification	E1.9	E1.12
Gears	9	12
Gear range	568%	600%
Approx. weight	4.0kg	4.1kg
Peak power	600/800W depending setup	600/800W depending setup
Torque	85Nm	85Nm
Electronic shifting	Yes	Yes

Pinion also specifies an oil-change interval of 10,000km for the system.¹

The unit is heavier than a standalone mid-drive motor, but that comparison is incomplete because the MGU replaces the cassette, derailleur, shifter and parts of the conventional drivetrain.

The biggest advantage is removing vulnerable rear components

A traditional derailleur hangs close to rocks, curbs and transport damage. On an eMTB, it also handles high chain tension created by combined rider and motor power.

Moving gears into the central housing offers several benefits:

• fewer exposed precision parts;
• cleaner rear-wheel design;
• potential belt-drive use;
• lower unsprung/rotating complexity at the wheel;
• electronic shift control coordinated with the motor;
• reduced routine drivetrain adjustment.

For trekking and commuter bikes, reduced maintenance may be even more valuable than off-road durability.

Electronic control enables functions mechanical derailleurs cannot easily match

Once the gearbox is electronically shifted and integrated with the motor controller, the system can coordinate power and gear choice.

Pinion offers functions such as preselection and start-gear logic through its Smart.Shift ecosystem.²

The motor knows the current gear and can briefly manage torque during a shift. That can reduce the harsh load spikes that occur when riders shift conventional derailleurs under full motor assistance.

Avinox’s MG Concept pushes the idea further

At Eurobike 2026, Avinox introduced its first MG Concept in collaboration with several bicycle brands.³

The company says the concept can:

• shift in less than 0.1 second;
• shift under high-torque pedaling;
• shift while stationary;
• support single or multiple gear changes;
• use manual, cadence-based automatic or AI+ automatic modes;
• eliminate a conventional rear derailleur and multi-speed cassette;
• use a single-speed chain or belt;
• lock the motor for anti-theft protection even without normal drive power.³

It remains a concept, not a production specification. That distinction is important. But the fact that major bike brands collaborated on the project suggests serious OEM interest.

Why high-power motors make gearboxes more attractive

As motor torque rises above 100Nm, drivetrain load becomes harder to ignore. Avinox’s current M2S can claim up to 150Nm in Boost under specified conditions.⁴

A conventional chain and cassette can handle impressive loads, but repeated shifting under motor power accelerates wear. Integrated gearboxes allow the drive-system supplier to control both torque generation and gear selection.

That is a major systems-engineering advantage.

The weight problem is real

MGUs are not automatically lighter. Pinion’s E1.12 is around 4.1kg, substantially heavier than many standalone mid-drive motors.¹

But a fair comparison needs to subtract the components it replaces. A rear derailleur, cassette and shifter can together weigh well over 1kg depending on the group, and an MGU may enable a simpler rear wheel and belt.

The more important question is total system weight and distribution, not the isolated motor housing.

Efficiency can vary by gear

Every gear mesh introduces losses. A gearbox with multiple internal stages can have different efficiency in different ratios.

This means MGUs must compete not only on convenience but also on range. A conventional derailleur drivetrain is mechanically efficient when clean and properly aligned.

For long-range trekking bikes, even a small efficiency penalty can matter. Independent controlled testing will therefore remain important as more systems reach market.

Service becomes centralized

A sealed gearbox protects components from dirt and impacts, but it also changes repair behavior.

With a derailleur bike, many parts are standardized and can be replaced by almost any shop. With an MGU, a critical motor/transmission failure may require authorized diagnostics or unit-level service.

The buyer is therefore trading frequent simple maintenance for potentially less frequent but more specialized service.

That makes supplier network and long-term parts support strategically important.

Frame design must commit early

A bicycle frame built around an MGU cannot easily swap to a conventional mid-drive late in development. Mount dimensions, chain line, suspension layout, belt path and software integration are architecture-level choices.

OEMs considering MGUs should therefore evaluate:

• supplier longevity;
• service network;
• replacement-unit availability;
• firmware support period;
• battery compatibility;
• diagnostic tools;
• licensing and integration requirements.

The technology is attractive, but platform lock-in is higher.

Which categories benefit most?

eMTB

Protection from impacts, centralized mass and controlled shifting are compelling.

Trekking

Low maintenance, wide gear range and belt-drive compatibility may be even more important than outright performance.

Cargo

High loads and frequent stop-start riding make automatic shifting and stationary shifts useful.

Urban commuter

A sealed low-maintenance drivetrain is attractive, but cost needs to fall before MGUs become mainstream in value-focused city bikes.

Will derailleurs disappear?

Unlikely in the near term. Derailleurs are light, efficient, familiar, inexpensive at scale and easy to service. They will remain excellent for many bicycles.

The more plausible future is segmentation. Lightweight e-bikes may keep conventional drivetrains. Premium trekking, cargo and full-power eMTBs may increasingly adopt integrated gearbox systems where durability and software control justify the cost and weight.

Bottom line

Motor-gearbox units solve a problem created partly by the success of the e-bike motor itself. As electric assistance becomes stronger, the conventional exposed drivetrain has to handle loads it was not originally designed around.

Pinion demonstrates that an MGU can work as a production product; Avinox shows how quickly competitors are exploring the same architecture. If weight falls and service networks mature, integrated motor-gearbox systems could become one of the defining e-bike technologies of the late 2020s.

Sources

Image: Wikimedia Commons. Verify license and attribution on the source page before publication.

Footnotes

1. Pinion, Motor.Gearbox.Unit E-Drive system. https://pinion.eu/en/e-drive/ ↩ ↩² ↩³

2. Pinion, E-Drive Technology. https://pinion.eu/en/e-drive/technology/ ↩

3. Avinox, “Avinox Unveils the Avinox MG Concept Product at Eurobike 2026.” https://www.avinox-ebike.com/news/avinox-concept-product-eurobike-2026 ↩ ↩²

4. Avinox, Drive System FAQ. https://www.avinox-ebike.com/avinox-system/faq ↩