Riding motorbikes is serious business. Riders can agree aloud with one another that it’s all just about being out there, enjoying the scenery, the engine noise, and the company of fellow leather-clad men and women all they want, but that’s not the whole truth and they all know it. Numbers also matter. How fast, how loud, how light, how powerful. How many kilometres per hour, how many decibels, how many (or how few, rather) kilograms, how many horsepower – and at how many revolutions per minute. In science, they call that quantitative analysis, and riding is a science. You’re good at it because you think about it, or, if you don’t, because someone else has thought it through long before you ever got on a bike.

Understanding the numbers helps us understand bikes – humble specs might mean big riding fun from a bike that’s easy to max out, impressive specs could belong to a real handful of a thing.

What better place to start than engine output – power and torque. What are they? What do they mean for what a bike is like to ride? That last question will have to wait for the next instalment, when we consider power and torque curves, rev ranges and gearing ratios – the stuff that affects how an engine actually pushes a bike along. For now, we’ll focus on the meaning of the terms “power” and “torque”, settle on which units of measurement to use for them, and what values are plausible for different bikes.

Torque

In the great oral tradition of pub wisdom, torque is something Italian V-twins and British triples make; power comes from Japanese inline-fours. This is, of course, rubbish.

If a force acts on an object and causes it to spin – such as happens, say, with the crankshaft of a motorcycle engine – that’s torque. All engines make torque, measured in pound-feet (lb-ft), kilogram-metres (kg-m) or Newton-metres (Nm). The current batch of litre sportsbikes, for example, manage to chuck out a maximum of around 11kg-m of torque on the dyno. To understand what this quantity means, imagine ripping the bike’s engine apart and rearranging it so the clutch was on the end of the crank instead of behind it, on the gearbox input shaft… better yet, let’s consider BMW’s G450X enduro bike, which is already built this way. It generates just on 4kg-m of torque at 7500rpm or so. Now, take a steel rod two metres long and attach it to the clutch so the motor spins it like a propeller. Next, hold the rod horizontal, and stick a 4kg weight on one end of it. Finally, rev the bike to its maximum-torque rpm, feed in the clutch and pin the throttle to the stop. The rod and the weight, attached to the slipping clutch, won’t move. The torque of the motor trying to lift the weight will just balance gravity pulling it down. Add a bit more weight, and gravity wins. Lop some off, and you have a sort of an impractical catapult.

4kg – or the litre bikes’ 11kg – might not sound like much, but try holding it out on the end of a stick a metre long. Then, while you’re massaging your strained shoulder afterwards, consider that inside the engine, the forces which result in that torque act on crankshafts with a throw of less than six centimetres. The burning fuel-air mixture inside the 450’s cylinder pushes on the piston and spins the crank via the conrod with an average force of over 80kg – and it peaks a lot higher than that. In a litre-bike engine, the force is well over 200kg.

Still, because 11Kg-m does sound small, Dailybike’s units of choice for quoting torque is the Newton-metre, as read on the scales of torque wrenches in sheds and workshops the world over. 1kg-m is 9.8Nm, so the litre sportsbike making an unassuming 11kg-m of torque also makes a much heftier-sounding 107.8Nm – a whisker less than the 110Nm the 200cc-bigger World Superbike-compliant V-twins manage.