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Paul Roberts

Let’s Talk about Torque

Oh dear, where do we start? HP, BHP, Torque, Kw, NM, lb/ft? It sounds tough, but we promise to be easy on you and try to make the age-old argument between torque and horse power, at least, a little bit easier, or dare I say it, irrelevant!

This becomes all the more crucial when considering an electric vehicle, because EV's can produce so much more torque from a relatively lower hp (horse power) motor. Which makes comparing them to an ice (internal combustion engine) bike, a bit difficult.


It's not so much, 'what's the difference between torque and horsepower?', because our engineers can talk on that subject all-day-long using trajectory sums and engineering speak. It gets pretty boring to be honest. But when it comes to describing the difference in terms of rideability, and which you should be considering when buying your next e-motorcycle or e-scooter, well, we're putting our thinking caps on.


We'll do this two ways. The complicated and accurate way, and the easy, and not so accurate way. If maths isn't your thing, don't hold too tight, we haven't dived too deep.


The Complicated and Accurate Way

What Is Horse Power?

Horse power is a measurement of the total power output of a system. Let's say, your motorcycle or scooter engine. While it can be calculated from torque, this involves a numerical constant and a time element that results in the two measurements not being aligned. Put simply, they are measurements of different things. If this wasn't the case then we probably wouldn't be having this discussion, but they are different beasts and shouldn't be compared.

The calculation for BHP from torque, goes like this: BHP = torque X rpm/5252.

In the equation above you'll see 'rpm' - revs per minute - the 'per minute' part of the equation adds the time element. It gets pretty complicated and we don't need to worry about this for now. Let's stick with hp as a measurement of the total power output of a motor. This includes forward force / torque on the axle and speed.


What Is Torque:

Torque, on the other hand, is more specific, it represents the load a motor can handle to generate a certain amount of power to rotate the motor on its axis. Lets call it 'the turning force of the motor'. The rear axle on your e-motorcycle or e-scooter is a great example. Torque is calculated on a vector, which makes it quite different from hp. The equation for torque is:

In this equation for torque, r = radius, F = force and 0 = the angle between F and the lever arm. Lets not get too bogged down in this. As you can see torque is different from hp and therefore, ideally they aren't compared side-by-side. Now let's move on to the easy, but not so accurate, bit.


The Easy, But Not So Accurate, Way

What is HP?

As we mentioned previously, hp can be considered as a total power output of the motor. It takes into consideration the speed and the torque. It's a great way to judge the general or overall ability of a motor. If you buy a higher hp engine, you'll probably get higher torque and higher top speed. (when compared to the same engine with lower hp).


What is Torque?

Torque is the acceleration you feel when pulling away. Its an exact calculation of the power output in the rear axle and will serve you well when doing side-by-side comparisons. The more torque, the more acceleration (g-force) you will feel and the faster you will get to the speed you require.


Top Speed:

Hp includes a speed element, so should we. Once you know the top speed, you can be assured that in an electric vehicle, there's almost full torque all the way there.

With torque and top speed information you can almost bypass horsepower and kilowatts.

A Brief Tangent:

Just while we contemplate the meaning of all this jargon. Lets quickly look at kw, (kilowatts). An often used term in the EV industry. Kw is similar to HP in that it is a total-power measurement. And it is true that Kw and Hp are directly related (mathematically) e.g. 100hp is 74.57Kw and always will be. However the difference is how the vehicles and motors are measured by the industry and regulators in the UK. For traditional ice bikes and scooters, hp is measured as the maximum power output of the vehicle, this means in ideal conditions and at the right revs. (it's the most they can get out of the engine),


Whereas Kilowatts in a 2 wheeled EV are measured continuously. This is the maximum power output that the motor can sustain for 30 minutes. This leaves room for more power to be available, should you wish to push your motor closer to the limit, albeit for limited or reduced periods of time. This is why e-motorcycles and e-scooters have continuous - sometimes called rated - power and peak power in their statistics.


So What Should We Do?

We recommend that both are important, but maybe not equally.

Stanford R3e Top Trump
Stanford R3e Top Trump

HP:

HP will give you a general and overall idea of what the engine is capable of. A larger hp or kw motor will probably give you more torque and probably give you a higher top speed. But without those details, you can't tell from hp alone. This is important because different machines are built for different thrills. So not checking the details could leave you dropping thousands on the wrong bike.


Electric Vs ICE Comparison:

The above point is important when comparing a traditional ice motor with an electric counterpart. As an example, the 12.5kw (16.7hp) SurRon Light Bee X (electric) comes to mind with it's massive 250nm of torque. If we compare this to an ice bike, lets say the Honda VTR1000 (SP1). The Honda has a 136hp (101kw) engine and delivers 96.28nm of torque. Okay they are different machines built for different thrills, but you get the point, the details mater. In the example above, the Honda's power is in the speed. Topping-out at 164mph. Whereas the Light Bee X can only reach 46mph.


And Finally, What About Torque Then?

Always check the torque! It's a crucial data point that you should know. Especially if you are interested in acceleration and the thrill of riding any e-motorcycle or e-scooter. It will tell you how fast you can get to top speed. It will also tell you what kind of g-force you will feel as you pull away from the lights. Also, and equally as important, check the top speed! These two together will give you a much better 'real-life' idea of what you'll be riding.


We have our own calculation for toque. It's:

more torque = more fun.





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