"For every action there is an equal and opposite reaction"..................Isaac N.

All of the motors on this website come with a torque arm. It is 100% necessary to install the torque arms!! (possible exception is P4 motor) Why use torque arms and torque washers?........glad you asked!

The axles on the hub motors have two flat sides which slide into the slots of the bike frame (the slots are other wise known as dropouts). The axle of every hub motor is designed to remain stationary (i.e they do not rotate , the motor rotates around the stationary axle). Because most of the motors can develop quite high torque it is very possible (almost inevitable in fact) that the axle will eventually start to rotate in the slots (dropouts) due to this very high torque.. 

This is in part due to the leverage effect ( well its something to do with torque = force times distance )
The diagram below shows a hub motor and its axle , bike tyre and part of the bike frame. On the bottom right I've drawn a closeup of the axle

think of it this way: lets say you try and stop the motor rotating by holding the wheel with your hand, it will be hard to do but likely you can stop it turning. Now imagine the motor has no spokes or rim, you use your hands to stop the motor rotating just by holding onto the motor, you haven't got a chance of stopping it!!
The force is much higher the smaller is the circumference of the turning circle.
The radius of the turning circle at the outer edge of a 26" tyre is 325mm, the radius of the turning circle where the axle touches the bike frame is only 6mm, so the force is huge in the order of 50 times the force at the outer edge of the tyre. Hence you really need to use torque arms!!!
 

What happens if you don't use the torque arms:
1. at some time is very likely the axle will turn inside the bike frame even if you have it in their very tightly.
2. when the axle gets to a point where is going to rotate in the frame it usually happens very quickly. When it happens the axle rotates and the wires coming out of the axle wrap around the axle very quickly and get wound up like wire on a fishing reel. The wires will either pull out of the motor or break somewhere else.
It means a very big repair job either way, so it really is worth the time to install the torque arm(s) and torque washers.

How to Install the Torque Washers and Torque Arms:

1. Torque Washers:
Below is a picture of a torque washer. Every motor I sell has torque washers on either side of the motor. The torque washer is quite thick steel and has a lip on it. This lip sits inside the dropout slots and provides some added protection against the axle rotating. Picture below shows a 12mm diameter axle ( some hub motors use 14mm dia axles).

Usually it will be necessary to bend the lip over to 90degrees to make the lip fit neatly into the dropout slot. You'll need to do that with a big hammer and a vice. So one washer should be used on each side of the axle. (I've recently discovered you can on some motors put two torque washers on each side, one on the inside of the frame and one on the outside of the frame but one torque washer each side is sufficient).
 ( Postscript: On some bike frames you can also fit a torque washer on the inner side of the frame, so it is possible to use 4 torque washers on a motor but requires grinding/filing off some of the lip, as having a torque washer on the inner and outer side of the bike frame when you tighten the nuts the lips of the inner and outer torque washers touch and require filing back so the torque washers can be flush on the bike frame when the axle nuts are tightened.....hope that makes sense!)

2.Torque Arms
Below are some pictures of the torque arms I supply. These are the type commonly available in china.

The central hole which goes onto the axle has a flat section on each side to hold the axle in place firmly. Most hub motors have a 12mm diameter shaft the flat sections being about 10mm across. There are also 14mm diameter shafts and the flat section is 12mm across. So if you want to buy some torque arms I need to know what is the diameter of your axle.

How to install the torque bars:

Because bikes have many different angles at which the dropouts (slots in frame where axle goes) are aligned it means there may be some diy work to install the torque bars. Heres a few ideas of how to install them. Its really up to the customer to solve how to instal them. It would be possible to have a universal torque arm which would work on any bike ( I have a design in mind but haven't organised anyone to make them as yet).

This is Brian of Melbournes method, I think this is an excellent method, this system could be used to make a torque bar which would adapt to most rear bike frames (something I'm hoping to be able to offer at some stage in the future, something similar to this).

Below I've joined the torque bar to the vertical arm of the rear carrier which a hose clamp, it was necessary to grind out a recess so that the hose clamp wouldn't move up or down. Rear carrier is not really the ideal way to connect a torque arm but will work on some bikes.

Neddie in Sydney made his own torque bar using the pre-existing threaded holes in the bike frame to keep it in place.

The torque arms can also be used on the front forks. It requires the use of hoseclamps to keep in place and some bending of the torque arms is necessary to get them to sit nicely  next to the front forks. They are 4mm thick metal so require substantial force with a hammer to change their shape.

A More Technical Method of Installation of Torque Bar

Heres a method (in detail) for the more technically minded. It requires some cuting and welding of the torque arm but gives a nice result which will suit your particular frame.

Installing the torque arm. The torque arm is a necessary part in order to assure the axle will not rotate in the bike frame. If for some reason a torque washer does not work correctly then the torque arm is an added precaution.
This is only a suggested way to install the torque arm. Because there are many variations in rear frames its quite difficult to get a torque arm that would fit any bike frame, so heres one method I"ve used  to install a torque arm.(this method requires a welder).

Cut the torque arm ( with hacksaw) into two pieces as shown below.

Install the flat piece onto the axle as shown below .
Note all pictures below show the bike frame upside down except for the last two pictures at bottom of page.

Place the other part of the torque arm so it sits next to the bike frame where it will later be held on by hose clamps. In this case i've made a spacer tube but the torque arm could be flattened out so a spacer tube is not necessary.
 Two views shown below lining up the two pieces for a tab weld.

Cut the end of the torque bar which is sitting along the bike frame in the pic. below (on right in pic below) so that it will join neatly to the torque bar that is sitting on the axle.

Place some tape on the bike frame to protect it from scratches. Using plastic cable ties or similar to hold the horizontal torque bar in place so that it sits right next to the torque bar on the axle. Then just do a tack weld to hold them together.

Remove the torque bar and make a weld to join the two parts together as shown below (dont weld while on the bike the paint might be damaged).
Picture below shows torque bar back in position after being welded off the bike. Make sure the weld is a very strong one. Hit the weld with a small metal hammer numerous times to remove slag and relieve stresses inside the weld (this will also test to see if the weld is strong!).
 

The finished weld shown below (a bit rough!), two hose clamps the same as you find on radiator hoses will be required (dont use aluminum type hose clamps they are very weak, use steel ones) one hose clamp might be ok but I would use two just to be sure.

Put the torque washer, spacer tube (not required if torque arm is flattened by hammer to suit the frame) and torque arm on the axle with the nut.
 

The finished torque arm with the bike turned up the right way on its wheels. Note the torque washer is not really visible in the pictures below as I placed it on the inner side of the bike frame to move the wheel centre over just a few mm more (the tyre was almost rubbing on the bike frame on one side).