Converting a Trekking Bike to an E-Bike

A trekking bike with standard dimensions is the easiest basis for a conversion. A 622 wheel, 100 mm hub spacing at the front and 135 mm at the rear, a derailleur and a down tube with room for the battery: front, rear and mid-drive motors all fit. With this bike the question is less "does it work?" than "which motor suits you?".

What makes a trekking bike

Trekking bikes usually have a diamond frame in aluminium or steel, 28-inch wheels (ETRTO 622), quick-release axles, 7 to 10 gears with a derailleur and often a rack and mudguards. Our example bike: aluminium, 16 kg, hydraulic rim brakes, 9-speed, 460 mm down tube.

What usually works

• Hub spacing: 135 mm at the rear is the usual value for hub motors (Fahrrad XXL), and 100 mm at the front.
• Derailleur: rear motors need a screw-on sprocket block or a cassette body, and the number of gears has to fit. Mid-drives keep using your gears.
• Bottom bracket: a 68 mm BSA shell fits the common mid-drives, see Measure the bottom bracket.
• Room on the down tube: frame batteries often need 35 to 45 cm, which is a rule of thumb. Our example bike has 46 cm.

For the example bike the configurator rates the front, rear and mid-drive motors green, and the verdict is "convert".

What it can fail on

• Brakes: mechanical rim brakes reach their limits with extra weight and speed, and hydraulic disc brakes are best (GIGA). With hydraulic brakes you usually need a magnetic sensor for the motor cut-off, see Brakes.
• Carbon: a carbon frame is not a suitable candidate.
• Weight: kit and battery often weigh 6 to 8 kg. Check the permitted total weight of the bike and the rack, see Frame and weight.
• Wear parts: replace an old chain, sprockets and tyres first, especially before a mid-drive, which puts more load on chain and sprockets.
• Small frame: the battery does not always fit in the frame triangle. Measure before you order.

Which motor type fits

For the example bike (15 km a day, 150 m of climbing) the configurator recommends the mid-drive. Upway names the most natural ride feel and plenty of power on hills as advantages (Upway). The comparison in detail: Mid-drive vs hub motor and Motor types.

What to measure first

1. Bottom bracket shell and bracket type, see Measure the bottom bracket.
2. Hub spacing at the rear and front, see Hub spacing.
3. Rim size on the tyre, see Wheel sizes.
4. Room on the down tube for the battery, see Battery.
5. Cassette: number of gears and mount (screw-on or freehub body).

The law in short

Pedelec means: at most 250 W rated continuous power, assistance only while you pedal, up to 25 km/h. A throttle is only allowed as a walking aid up to 6 km/h, anything above is a motor vehicle. See Pedelec law.

When you should leave it

Leave it if your bike is carbon, the frame has cracks or heavy corrosion, or the brakes are already poor without a motor and you do not want to replace them. With a very cheap bike, where kit and brakes cost more than the bike is worth, a used e-bike is often the better bet. The manufacturer's warranty mostly lapses, and some workshops refuse conversions.

How sure is this?

The statements on hub spacing, brakes, weight and warranty come from the sources listed. The battery's space needs, wear on a mid-drive and the weighing of motor types are assumptions and rules of thumb that Fabio is still checking. The assessment of the example bike comes from our configurator.

Does a conversion fit your bike?