Efneo’s GTRO
is a 3-speed planetary gearbox.

Gear ratios and shifting

GTRO’s 1st gear is neutral (1:1). Second and third gears are incremental. On 2nd gear chainring rotates 43% quicker than on 1st gear. On 3rd gear chainring rotates 79% quicker than on 1st gear. This way you can easily calculate real chainring size on each gear.

For any other chainring or beltring, follow the same scheme to calculate 2nd and 3rd gear size.


To know more about GTRO:

Bottom brackets
Crank lengths
Chainline / belt line ranges
Sprocket / beltring types and sizes
Compatibility with cadence and torque sensors
Chain size compatibility

Click HERE to open a new window with the latest details.


Folding bikes

At this moment GTRO is positively tested for compatibility
with these great folding bike brands:

Compatibility tests include full folding and unfolding procedure with a GTRO installed. We test GTRO on other folding bikes and will add other options to our shop cart soon.
If you have another folding bike and wish to have a GTRO on it, please e-mail wiktor(małpa)efneo.com with your brand and model name.


Trikes & recumbents

GTRO was tested on trikes and recumbents of many different brands, including:

If you have another horizontal bike and wish to have a GTRO on it, please e-mail wiktor(małpa)efneo.com with your brand and model name.


Rear transmission / hub

Compatible with:

01 All rear casettes

02 Zehus Bike+ engine with chain sprocket

For the purpose of turning it on with backpedalling.

03 All rear hub motors

More on cadence and torque sensor compatibility in the Options document.

04 All internally geared hubs (IGH)

Like Shimano Nexus, Shimano Alfine, Sturmey Archer, NuVinci Enviolo, Rohloff. Please remember to check manufacturer’s manual what is the smallest size of a front chainring recommended for your IGH.

Not compatible with:

01 Mid-drive engines

Like Bafang, 8Fun, Shimano STEPS, Bosch, etc.

02 Coast brakes and fixie bikes

GTRO has a freewheel integrated inside. When backpedalling, the torque is transmitted at a very low value.

Maintenance and durability


GTRO passed an ISO 4210 test for bicycle cranks in SGS laboratory.


GTRO is sealed with three dynamic seals (including two v-rings) to protect it against water, dust, salt and sand.


No additional lubrication necessary after installation.

For bike builders and designers

If you plan to build a new bike and you think GTRO may be a good option for you, often a 3D CAD model may be the best first step to play with GTRO on your computer design board.
Please email wiktor(małpa)efneo.com to get a link to 3D .step files.