Understanding the brake size of a hub dyno.
Choosing between Small and Medium hubs can be confusing – how much brake capacity do you actually need? At first glance, seeing that the Small hubs have 3500 Nm per axle might make you think, “Where can I even find a car with 3500 Nm of torque?” But here’s the catch: we’re talking about hub torque, not engine torque!
First let’s take a simple real-life example: While driving on the street, especially on slippery surfaces, with 1st and 2nd gear your car can easily spin the tires, but in higher gears, even with the same engine torque, the wheels don’t break traction as easily, that’s because the torque reaching the wheels is lower. Your gear ratio multiplies the torque! The torque at the wheel hub is significantly higher than the engine torque because of the car’s gear ratio.
Ok, but while driving on the dyno I can choose a gear that is 1:1 or even overdrive, so why do I care about this? Because the final drive does the same thing! And that is very often fixed, so you cannot choose what ratio you want to use (and no 1:1 option even exist).
Let’s say your car makes 500 Nm of engine torque, and the final drive ratio is 5.0:1. That means the torque at the hubs is already:500 Nm × 5.0 = 2500 Nm at the hubs (in 1:1 gear ratio).
Suddenly, 3500 Nm per axle doesn’t seem so big anymore, right? That’s why understanding what level of torque the dyno is able to control is not that simple as the dyno needs to handle real-world hub torque, not just engine torque!
