Get to grips with preload

the road, they’re just unpleasant. At the other end of the spectrum is my Yamaha MT-07. It has very soft springs and soft damping, so on the same bumpy roads it moves around on its springs all the time. I can live with that, because the shock absorption is so good - I never get a violent thwack through the bars.

The best bike I have ever tried for ride comfort was a 2003 Yamaha XJR1300. At 60mph it felt like a magic carpet. The springs at this speed were just ideal for my 13 stone in riding gear. So if you feel curious about how good or bad your suspension is, ride several different bikes. One of them will feel nicest. If it’s yours, great. If not, get tweaking. Understanding preload can feel like grabbing an eel in the bath. Try this: Push down on your bars. They will bob back up and settle. Let’s say the forks have been designed with 120mm of down-and-up travel and the settle point is 15mm from the top of that travel (aka full extension). Hold the idea of that ‘settle point’. Now turn the preload adjusters clockwise, to increase the preload a bit. If you measure the settle point now, you’ll see it’s changed. Instead of 15mm from full extension, it might be 10mm. So the front of the bike sits a little higher than it did. Same principle with the rear.

Preload adjustment compensates for the extra weight of things like panniers, passengers or crates of beer, so that you restore the bike’s ideal attitude. But it’s also worth fine-tuning for solo riding, to make the most of the suspension.

How to set preload

Your preload is right when your suspension is using a third to a quarter of its travel with you on board, in your riding gear, sitting in the normal position.

To establish that, you ideally need a mate with a hydraulic work ramp that can clamp the rear wheel. This fixes the bike in an upright position, which makes it easy to measure small changes accurately. Otherwise you will need someone burly to hold the bike upright, and someone reliable to record the measurements. We’re assuming your bike has 120mm suspension travel both ends (but you can check your owner’s manual, which should confirm the travel), and we’re ignoring the fact that on most bikes, adjusting rear preload is a knuckle-skinning nightmare.

First, with the bike in position, fix a horizontal bar above the rear wheel spindle. Write down the distance from the bar to a marked reference point on the bike above the rear spindle (such as the bottom edge of a grabrail). Now lift the rear end until it is fully extended. Write down the new distance. The difference is called static sag. Adjust the preload until it is 10-15mm.

Now sit on the bike and repeat the measuring. The difference between this measurement and the static sag is the dynamic, or rider, sag. It should be 30-40mm. If you can’t find a preload setting that gives the right values for both static and dynamic sag, your spring rate is wrong for your weight.

Now repeat the process for the forks. Instead of measuring from a horizontal bar, use a cable tie round the stanchion to record the three measurements you need. Static sag should be 20-25mm, and rider sag, 30-40mm. Again, if both can’t be achieved together, it would be a good idea to get the springs changed.

What is damping?

Springs on their own give an endlessly boingy ride. Damping imposes a drag to make the spring movement useful. Fine-tuning makes a big difference to how your bike feels. Damping works in both directions: compression (when your forks dive or your shock squashes down) and rebound (when they extend to return to their default position).

Now, the trouble with motorbike suspension is it does two entirely separate jobs. First, it insulates you from the force of crashing over bumps (ie soft damping). Second, it controls the bike’s attitude under braking, turning and acceleration (ie stiff damping). Soft

“Getting springs right can be the best money you spend”

damping is usually more important on the road. On the track, it’s hard damping. As a general approach on the road, use the lightest damping you can get away with while still keeping control.

You stiffen or soften damping by turning a screw in or out. Always start with the factory setting and write down what you change so that you can go back if needs be. Record the number of turns (or clicks) from fully screwed in but make sure you don’t tighten the screw too hard and lock it up.

Optimise your damping

Find a twisty test route, take a screwdriver and adjust one of the following four each time, before checking the results on a test ride. Finish adjusting one thing before moving onto the next. Always write down every change and your impressions. When you eventually discover that you have gone too far, you can go back one step to the previous setting.

Fork compression: soften gradually until the front dives too much under full braking. Fork rebound: soften gradually until the front rebounds too much as you let the brakes off into a corner. Rear compression: soften gradually until the back end squats too much accelerating hard out of a bend. Rear rebound: soften gradually until the back end pogos accelerating hard out of a bend.

First establish a datum point off the bike to measure the rear sag against. Adjust the preload to give a static sag of 10-15mm.

Do the same at the front but in line with the forks. Again, if the springs are correct, the difference should be 10-15mm.

The rider sits on and the difference between static and rider sag should be 30-40mm. If not, the springs are wrong for that rider.

One holds the bike upright, one takes measurements and someone notes them down If you’re really lucky, your bike will have an easily accessible manual adjuster for rear preload

Most bikes use a stepped adjuster for rear preload, so tools and kevlar knuckles are required Most forks, like these Showa BPFS, have easy adjustment for compression and rebound damping