Sort your springs
Do you suspect you’re not getting the most from your suspension? Here’s a bite-sized gallop through the main issues
IN ITS SIMPLEST terms, for most road riding, a motorbike (and its rider) can be thought of as a lump of metal, flesh and leather with springy projections at the front and back. Each of these springy bits is attached to a wheel, and each wheel moves up and down over bumps so you don’t have to.
There’s more to it than that, of course: there are also linkages, damping systems, and even electronic control units on newer bikes to consider. But never mind that for the time being. The most important bit of your suspension is
the springs. If they are the right stiffness for your weight, bike and riding style, every ride will feel really nice. If your springs are too soft, the wheels move too far in response to bumps, as if you were riding a blancmange. If they’re too stiff, the suspension transmits the shocks directly to your wrists and arse.
Of course, a one-inch bump at 30mph produces a fraction of the force of the same thing at 100mph. Not only that, but bumps come in every size and profile. Nevertheless, there is an ideal spring rate for you - and it may or may not be the one your bike came with originally.
Being a nerd, I spent three years experimenting with springs on my 1998 Ducati 900SS. I ended up with 0.8kg/mm springs in the forks and an 8kg/mm spring on the shock. As the bike came from Bologna, the dual-rate fork springs were 0.62kg/mm for most of their travel, and the shock spring was 8.5kg/mm. The numbers are less important here than what they actually illustrate: your bike manufacturer’s spring choice might work for you or it could be improved on. You can find out by experiment, by looking at an online calculator (see www.racetech.com), or just by speaking to your nearest suspension specialist. Trust me, getting your springs right can be the best money you will ever spend on your bike.
The importance of springs
My friend Dave recently bought a Triumph Thruxton R. After his first ride on bumpy roads, he could not believe how uncomfortable it was. So he went on the forums and found lots of other people had noticed the same thing. The springs at both the front and rear are very firm. On a trackday (the first of which he did last week) they’re ideal. On
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.