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If you’re absolutely clueless about what the suspension does, and what terms like “suspension sag” and “unsprung weight” mean, this episode is for you.
Tune in to discover:
- What the suspension actually does, and how it works
- 6 common terms related to suspension (including ‘suspension sag’)
Transcript
Hello and welcome to 30-minute motorcycling, a podcast for new, aspiring, and returning riders, we’ll you’ll discover something new about motorcycles and other two-wheelers in 30 minutes or less.
In this episode, we’re going to talk more about motorcycle suspension. Specifically,
The important job that suspension does
What a telescoping fork and a shock absorber consists of
And some terms related to suspensions, including sprung weight, unsprung weight, and if you stick with me to the end, you’re finally going to know what “suspension sag” really means.
First and foremost though, let’s talk about what your suspension actually does.
What your suspension does:
In a perfect world with perfectly smooth and maintained roads, there would be little to no need for suspension.
But that’s not the case – the roads are full of potholes, speed bumps, and bumps of other varieties,
And without suspension, your bike would be hard, if not impossible to control. Every time you’d hit something, the energy from the impact would travel up the handlebars and cause the bike to vibrate up into your shoulders and the wheel to bounce.
It’s not only uncomfortable – it’s also dangerous since the vibration and the bouncing can cause you to lose control. Therefore, the job of the suspension is to cushion you from the impact of these bumps and to keep your wheels in contact with the ground.
You’ll still feel those bumps, just not as much.
At the front, you have a pair of telescoping front forks.
Each fork leg has two metal tubes – one called the “moving fork slider” and one called the “stationary fork tube.”
The moving fork slider is usually made from aluminium alloy and has a slightly larger diameter than the tube it’s attached to, while the stationary fork tube is made from steel.
Inside each fork, there’s a long coil spring – which looks a lot like a spiral. When you ride over a bump in the road, the moving fork slider slides over the fork tube, which presses down on the coil spring, which in turn absorbs the energy from the bump.
Then, the spring releases the stored energy, decompresses the coil spring, and forces the forks back to their original position.
At the rear, you have a shock absorber. Or maybe you don’t.
If your bike doesn’t have any rear suspension, it’s called a “hard-tail.”
I’ve already done a podcast episode about hard-tails, so if you’re interested in learning more, please check out the episode about hard-tail and soft-tail motorcycles.
But I digress – what is a shock absorber?
Shock absorber
A shock absorber consists of a large coil spring (just like the one in the front forks), a hydraulic damper, and at least one swingarm or “swinging arm” which connects the rear wheel to the frame.
And as the name might suggest, a “shock absober” absorbs the shock from when your bike hits a pothole or some other thing on the road.
Just like the spring inside the front forks, the spring inside the shock absorber compresses and stores energy when your rear wheel hits something, and then uses that stored energy to decompress and return the spring to its original position.
So now that you know the basics of how your suspension works, let’s explain some common suspension-related terms, beginning with sprung, and unsprung weight.
Sprung and unsprung weight
Sprung weight is everything that is supported by the suspension. Some examples include:
- The frame
- The fuel tank
- The engine
Unsprung on the other hand is everything that the suspension does NOT support – such as:
- The wheels
- The tires and the
- The brakes
Generally speaking, the less unsprung weight your bike has, the better – the more unsprung weight you have, the longer it takes for the suspension to respond and react to bumps.
Of course, since your brakes and wheels are part of the unsprung weight, it’s impossible to achieve zero unsprung weight.
Suspension travel
Next, we have “suspension travel,” which is the difference between a fully decompressed fork with no weight on it (including that of the rider), and a fully compressed fork.
Off-road bikes tend to have more suspension travel than road bikes.
Preload
Next, let’s move on to “preload.”
The “preload” can best be described as the compression of the coil spring while it’s supporting the weight of the motorcycle and the weight of the motorcycle ONLY.
In other words, suspension preload does NOT apply when you or someone else is sitting on your bike.
Spring rate
A suspension spring needs a certain amount of weight to compress an entire inch (or 25 millimeters) – this weight is called the “spring rate,” which is measured in Pounds Per Inch for the Imperial scale or Newtons per Millimeters for the Metric scale.
Sag
And last, but definitely not least, we have “Suspension Sag.” Suspension sag is the distance the suspension compresses between a decompressed position to a full extension of the forks.
In layman’s terms, that means how far downwards the suspension can travel before it stops.
And that’s an overview of what your suspension does and some common suspension terminology. If you’d like to know more about suspension terminology, including the difference between “hard” and “soft” suspension. I’ve included a few links in the show notes that go into more detail.
If you have any more suspension terms that you’d like me to cover in a future episode, drop me an email at podcast@dualwheeljourney.com.
I hope you enjoyed listening, and above all that you understand a little bit more about motorcycle suspension. Hey – can you still remember what suspension sag is?
Either way, until next time, keep your helmet on, and your eyes on the road. Bye!
