What's the big Diff?

Introduction

What’s the difference between electric trikes that have a rear differential and those that don’t have a rear differential? Confused?

Let’s rephrase.

What is the difference between electric trikes, or any trike for that matter, that are built with a rear differential vs those built with a solid axle?

Unlike a two-wheel bicycle, a three-wheel pedal assist e-trike requires an axle that connects two wheels so that they operate in unison. In its simplest form a solid bar attached to the centre of both wheels and attached to the trike frame will be sufficient to form the basis of pedal driven transport.

In this very basic setup both wheels must turn at the same speed.  Therefore, as long as you are riding in a straight line, on an even surface you would be happy with the result. The downfall of this fixed axle is of course if you ever need to turn.

The Bigger Picture

Say you have a solid rear axle on your electric trike, but one of the two connected wheels is smaller than the other. Remember that the two wheels are obliged, due to the solid axle connection, to turn at the same speed.  The wheel that has the greater diameter will naturally cover more distance with a single rotation than the smaller wheel. What will result is a trike that simply goes around and around in circles.

Imagine now that the two wheels weren’t connected to each other but were independently attached to the frame of the trike. In this instance the smaller wheel would be able to spin faster than the larger one and once again you could travel in a straight line, albeit on a bit of a lean.

Now you might be thinking: Well, that’s ridiculous, who would put different size wheels on their electric tricycle and of course you’d be correct. Nobody would do that. However, the need for one wheel to go faster than the other occurs all the time even with wheels of the same size. Every time a trike turns left or right the outside wheel has more ground to cover than the inside wheel and therefore needs to rotate faster. Trikes with a solid axle can’t easily cope with this. Both wheels are the same size and both wheels are rotating at the same rate, but cornering requires a different result.

To accommodate, a solid axle trike must spin or hop the inside wheel to keep up with the outside wheel creating a jerky, unstable ride.  Add in acceleration or braking and the physics don’t add up.

A differential is a set of gears that transmits power from the motor to the wheels while allowing them to turn at different speeds. This then allows both wheels to be driven while allowing them to perform independently thus solving our slipping/hopping problem and providing a far more stable, comfortable, and safer ride.

Why aren’t all trikes built with a rear differential?

Why would anyone build a trike with a solid axle when the physics clearly identify a problem? The short answer? It’s cheaper, and easier.

When Little Johnny built his bright red go cart out of a wooden box and some lawn mower wheels, he didn’t go to the trouble of incorporating a differential for more stable cornering. The cart worked and in his youthful exuberance, a bit of wheel slip just added to the thrill.

When looking for an electric trike for adults in Canada you should expect a little more sophistication. So, can you build an e-trike without a differential and yet have the two wheels rotate independently? Yes, you can. You can bolt one wheel onto the frame on one side and bolt the other wheel onto the frame on the other side and they can spin at totally independent speeds. However, how are you going to drive both wheels? Without the wheels connected at all your motor or pedal power would need two chains and gear systems, one to drive each wheel. So, another cheap option is to build your trike without a connecting axle and then just drive one wheel. Can it work? Yes. Is it ideal? No. With only one wheel being driven you are sacrificing traction and control. Have you ever heard of a car setup like this?

The Solution

E-trikes with a differential are ultimately more stable, give greater traction and are overall much safer to ride. Yes, they may cost a bit more, but this is not Little Johnny’s go cart your riding, this is an enhancement to your lifestyle that hopefully you will still be enjoying in years to come. All of our electric trikes come with a rear differential. And that’s the diff.