Converting my Dawes Sonoran to an E Bike Part 2 - more about torque arms

I mentioned the need for a torque arm in the last post. Here's a bit more info and pictures.

The "drop out" into which the axle/spindle of a bicycle wheel fits is simply an inverted "U".  If the nuts holding the wheel in place become loose, the wheel will simply fall out.  Clearly this is not a good thing. Although the weight of the bike will hold it in place when stationery (and theoretically the weight of the bike and rider will hold it in place while moving - but only if you cycle on billiard tables !)

With a hub motored wheel, a new dimension arises. On an unpowered bicycle, the wheel simply rotates around the axle. No rotational force is applied to the axle. With a hub motor, the axle must be held firmly as the wheel is powered around the fixed centre.

This applies a considerable amount of rotational force (torque) and increases the chances that the nuts could work loose. As a result we need to ensure that the fixed centre of the hub cannot rotate in the dropout.

This is achieved initially by the fact that rather than the axle being round, it is larger than on a conventional bicycle and the sides are flattened to fix the axle into the slot of the drop out - is essence, the axle fits the dropout slot like a spanner fits a nut. As a result, the torque from the motor can even open up the drop out making this problem even worse - especially if the nuts themselves work loose.

This brings us neatly to the torque arm. A plate, fitted to the flattened off axle with an arm which is either jubilee clipped to the fork (an aesthetically awful solution) or bolted to a mudguard stay mount. The ones supplied by Panda are made by www.torque-reaction.co.uk and are magnificent pieces of machined stainless steel.

I selected a "multi-angle" torque arm for my Dawes Sonoran s the standard "eyelet style" did not reach the mudguard stay mount. An additional issue for my bike is that the stay mount and fork are in the same plane so one or the other needed to be packed out with washers to allow for the thickness of the steel plate. The official fitting videos show the "arm" fitted behind the "eyelet" but this means that the axle has to be packed with washers and I felt that this was an inelegant solution as well as leaving insufficient thread for the nut.

The alternative, placing the "arm" in front of the "eyelet" is a far neater solution although it does mean packing out the smaller M5 bolt with washers - and any force applied in the event of a loosened main nut will be applied to this weaker bolt.


I'll be keeping a close eye on the security of all nuts and bolts.