Advice: suspension setup part 2 – static sag

One of the most common subjects across the motorcycling sphere is suspension. As with anything to do with riding motorcycles, there are usually simple explanations for everything that happens, making it a matter of just taking the time to analyse each individual action and the resulting consequence.

In this forum we’ll just concentrate on ‘standard’ suspension, leaving an in-depth analysis of electronic suspension to another discussion.

In part one we took at a look at the suspension and its components, and this time it's static sag.

Static sag is set with the bike under its own weight, and is backed up by two further tests: the one G test (with rider and normal weight load in place), and measuring the amount of suspension travel used while riding.

To get the springing rates correct for your motorcycle, this process must be worked through in sequence. If you decide to miss one of the steps or allow the settings to fall outside the guidelines, you'll be missing at least one or more ingredients to getting your suspension working the way it's designed to.

So, let's discuss exactly what the static sag is. Static means motionless or inactive, pertaining to bodies at rest or equilibrium.

Sag means curve downwards under pressure. Hang loosely – so we are in affect measuring the "curve downwards of a body at rest".

The exact measurement for static sag at will differ from bike to bike, rider to rider, and will vary depending on how the bike is to be used. However, there are some basic guidelines on where to start.

First you need to know how much travel your suspension has by extending it fully and measuring in the direction of travel. On the forks this is easy as you simply measure from the top part of the lower fork leg to the bottom of the triple clamp.

On the rear, you need to pick two points that are at each end of the travel. For example, the grab rail and the axle. Unload the suspension fully by taking the weight off it and measure. This will give you the unloaded distance.

To get the fully extended length of the suspension, it's important that you take any sag out by lifting whichever end of the bike you are measuring. If possible, it's best to actually lift the wheel off the ground when doing so to ensure you are getting accurate measurements.

This can be done by having someone balance the bike of the side stand (if a centrestand isn't fitted) while you do the measuring.

Once you have this distance, stand the bike upright and allow it to sit under its own weight, measuring from the same points. It's best if you give the bike a couple of bounces up and down, and then allow it to settle before measuring. The difference between these two measurements is the static sag.

The rear sag should be somewhere between zero and 10mm, and the front between 20 and 30mm. As mentioned earlier, there will be some differences from bike to bike and rider to rider, depending on how you are using your bike, but it should always fall within this range.