Is the torque figure meaningless, or does it actually mean everything?

I know of a sim racing modder and blogger who claims that torque is meaningless.

As a marketing term, with no other information to contextualise that number, then sure, there's not really any useful meaning to be derived from a lonely torque figure.

Similarly, talk is meaningless without context. It's so staggeringly easy to take a quote and make it mean something different to what was intended by the person being quoted. If you need a real-world example of this just watch literally any episode of the ABC's Media Watch. They're calling people out for deliberately misleading their audiences in exactly that way, all the time.

Here's a simple example we can refer to later. "Babies can really suck." What does that mean? Is it referring to their mother's mammary glands or a feeding bottle? Or do I just hate babies and wish to hurl a schoolyard-style insult at them all? Or maybe I'm trying to be funny with a double-meaning?

Chassis dyno. The output at the wheels is what really matters. Photo: Shutterstock.

Chassis dyno. The output at the wheels is what really matters. Photo: Shutterstock.

Bringing this back to the topic at hand, torque, as a number on its own, with no other information around it, as used in marketing and motoring write-ups (guilty, albeit quite a while ago) doesn't have any useful meaning.

Once you provide the context though (and we'll explain in a moment that this context is the RPM of the engine, and the gearing of the drivetrain, because it's the output at the wheels that really matters) the torque has been given some useable meaning, in the same way that putting the aforementioned baby in the context of either happily feeding, or wailing on public transport until your ears bleed, or just a goofy statement in a comedy routine, gives the babies quote a useful meaning.

The aforementioned blogger, known to the Assetto Corsa community as Legion ("Mods are Legion for they are authored by Many", so named to acknowledge the work shared is that of many people) makes the statement "Torque is meaningless" by sharing two near-identical open-wheel race cars that you can download, add to Assetto Corsa, drive in the sim, and compare for yourself. One of these cars has lots of torque at the engine, but it only turns at low rpm (3250rpm limit) and it has tall gearing in the driveline. The other car has about a quarter as much torque at the engine, but it uses high revs (13000rpm limit) and short gearing. The interesting thing is, if you're a consistent driver you should be able to get identical lap times out of them.

This occurs because the driveline gearing also plays its part, and the end result is the same output at the wheels, and it's the output at the wheels that provides a vehicle with the ability to accelerate at a given rate.

To explain that a bit better, torque (whether it's the imperial pound-feet, or the metric Newton metres) from an engine is a twisting force, or a measure of work being done.

Power (whether it's the imperial horsepower, or the metric kilowatts) is a measure of how fast (quickly) that work is being done.

Mathematically, horsepower equals torque multiplied by rpm. The equation is P = T x RPM / 5252, where P is power, T is torque, RPM is revs per minute at the crankshaft, and 5252 is a constant (because of some complicated math that simplifies the equation to just use this number).

That will give you the output at the crankshaft (or flywheel), but we need to account for the gearing before it gets to the wheels.

The gearing is the same mathematically as a pulley system. Newton's laws of motion are usually taught by referring to horses, but off-road enthusiasts also know that if they add a simple single pulley to a winch, they can pull twice the weight but at half the speed (for a given rotational speed of the winch motor).

This occurs because that single pulley allows that work to be spread over double the distance (the winch has to do double the revolutions, but with the pulley only half the peak effort - torque - is required).

Gearing in a gearbox and diff work in much the same way, but at a different ratio to that single pulley. The shorter the gearing (the faster you require the engine to rev) the less peak torque is required to achieve the same rate of acceleration.

The two example sim race cars simply put different numbers in the equation for torque and RPM, and end up getting the same answers for power at the wheels.

This story Is torque meaningless, or does it actually mean everything? first appeared on The Canberra Times.