Electric Elephant (Bike)

The Pronto/Mailstair/Elephant bike is an excellent mini cargo bike but with one drawback, it's blooming heavy! This may not be a problem if you're bimbling around the fens but not if you expect to encounter hills. Adding a motor significantly enhances the usefulness of the bike!

Pashley now sell electric Prontos starting from £2435 (in 2023), but the same setup can be built at home for less than £1000.

### Motor Choice

One of the benefits of the Pronto is the internal gear hubs and drum breaks, both of which are reliable and low maintenance. To preserve theses features a mid-drive motor is essential. This slots into the bottom bracket shell and transmits power via the chain. Internal gear hubs and mid-drives go together well as the chain line can be optimised and a strong single-speed chain is used. The most ubiquitous mid-drive motor kits are produced by Bafang, speciffically the BBS series of motors. It's worth noting that the official e-Pronto appears to use a bafang BBS01. There are other manufacturers of motors, but Bafangs have a reputation for reliability, spare parts are readily available, and there is plentyful information about them on the internet.

It's worth noting that in order to remain street legal in the UK and Europe, a BBS01 is necessary, as this is rated to 250 Watts. The BBS02 looks identical but is rated to 500 Watts. Both of these can be programmed via a USB cable to vary the power and top speed across different pedal assist levels.

There's no need to cover installation in detail here, as there are plenty of YouTube tutorials online and the process is similar for any bike. JohnnyNerdOut channel has a particularly good video.

### Battery Placement

Usually the battery is either mounted on bottle holder bosses on the seat-tube or down-tube, or on a rear rack. The Pronto lacks a bottle holder mount but this can be retrofitted by drilling holes and fitting rivnuts (plenty of info on YouTube). I wanted to keep the rack clear and maintain a low centre of gravity, but I didn't have enough room on the down tube so I opted to place the battery on the seat tube. This works for me as I'm tall but please note this is the lowest the seat can now go!

The battery here is 14ah and 36v. Don't cheap out on batteries, you don't want to burn down your house. Get one from a reputable seller made from premium cells.

### Gearing

My elephant bike arrived with a 42T chainring and a 20T rear sproket. My bafang motor came with a 46T chainring, resulting in gearing set too high for my needs.

Mid drive motors work best when spinning at a high cadence. This prevents overheating and internal stress, and also delivers power most efficiently. For my use-case (very steep hills) I wanted very low gearing so I could climb hills at a good cadence in the lowest gear, and cruise on the flats at 15.5 MpH in the highest gear. Going down hill I'm happy to coast. To that end I installed a 24T rear sproket and bought an aftermarket 42T chainring from Precialps.

The 42T chainring is the smallest one that features a significant inboard offset without having to mess with the motor casing. This is important if you want to maintain a clean chainline.