Ask The Editors: Sprung Versus Unsprung Weight Explained

Does sprung versus unspring matter? Sure does.

You’re absolutely right and sure can. So we typically divide the weight of our machines into two specific categories based upon where it happens to exist upon the chassis – specifically whether it is above or below the suspension (hence the “sprung” designation).

Unsprung refers to the areas below the suspension’s range of motion – things like the tires and brakes and rims and sprockets.

Sprung, like logic suggests, refers to everything above the suspension – the frame, engine, plastic, seat, radiator and so on.

So why is sprung weight more influential than unsprung? Because by its very nature, it deals with a much higher center of gravity than the parts closest to the ground. The higher up you go, the greater the effect of factors like lean and roll. Mudders constantly deal with this tradeoff – they want machines as high off the ground as possible for maximum ground clearance but go too high and the platform becomes unstable and downright dangerous to turn.

One thing that’s particularly interesting about how we classify sprung versus unsprung is how do you quantify the suspension components themselves? Since they certainly carry significant weight and, like we discussed above, the whole thing is built upon whether the component in question is above or below the suspension’s motion line…we typically divide the shock right down the middle. The upper half falls into the sprung category and the lower unsprung.

This is why there are a few components considered “semi-spring” as well. Things like a chain that may swing around the countershaft above the suspension line (sprung) only to run down to a sprocket on the rear axle (unsprung).

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