Motorcycle chassis tuning 

In our experience, many motorcycle riders have never given any thought to their bike's suspension set-up. That's a pity because you can make your machine a lot more fun to ride, and much safer, with a chassis that's tuned to suit your personal riding style. It's also the reason that almost all motorcycles are designed with more or less adjustment options. Putting these to good use doesn't take any great mechanical skill or special tools. All you need to do is follow the steps described below and be willing to try out different things.

• The suspension set-up is not the only factor that affects how your motorcycle handles and feels. Before you start adjusting your suspension, first check that your tyre pressure is correct and the tread hasn't completely worn down. Both of these things can falsify the outcome of any adjustments you make. You should also check that the wheel, steering head and swingarm bearings have not got any play. And, of course, if your fork tubes are covered in an oily film and your shocks are leaking, then they're in need of repair rather than adjustment.
• The most important tools for doing any work on your bike chassis is a notepad and pencil! Be sure to make a note of your bike's existing set-up, which will usually be the factory set-up, and write down every single modification that you make to it. This is the only way to keep a check, make meaningful comparisons, and quickly return things to how they were if you're not satisfied with a change that you've made. You could also take photos with your smartphone to help with documenting everything you do. The other tools that you should have at the ready include: a folding rule or sturdy tape measure, screwdriver and open-end wrench for the forks, hook wrench for the shock absorber and, of course, the owner's manual for your motorcycle.
• If you can find someone to assist you, a second pair of hands makes many jobs a lot easier.
• Do like the professionals at the race track! Always proceed step by step and do a test ride after each modification you make. Remember: Experience comes from riding your bike!

Even when stationary, the weight of your motorcycle and load compresses the springs. This is essential to enable the suspension to always maintain ground contact. The degree to which the springs compress is called sag. To measure sag, you need to measure the distance between the bottom triple tree and the dust cap on the fork slider, or between the foot of the fork and the dust cap on upside-down (USD) forks. Take this measurement at the front of your bike twice, once with the suspension fully extended, i.e. unladen (Hu), e.g. by putting the bike on its centre stand, and the second time, preferably on a level surface, with rider and any luggage or pillion passenger, i.e. laden (Hl). It's best to get someone to assist you with taking the measurement on the loaded motorcycle.

For the rear sag, you measure from the wheel axle to a fixed point on the tail of the motorcycle, vertically above. Here too, measure once with no load (wheel off the ground) and once fully laden. The difference between each pair of measurements gives the sag. It should be around a third of the total travel when the bike is laden (Ttot). The total suspension travel is given in the technical data in your owner's manual. 

A: Fork offset

B: Trail

C: Rake

D: Wheelbase

Once you have taken the measurements described above, you're ready to start the test phase. Follow the instructions in the owner's manual and note down all the changes you make in your table. Usually the preload is adjustable by means of threaded spindles on both sides, which you screw in or out using an open-end wrench. Be sure to adjust equally on both forks.

On the shock, the preload is set either by a ratchet mechanism or by a slotted round nut with lock nut. Both are moved using a hook wrench, which is usually included in the tool kit that comes with the bike. Here again, if your bike has twin shocks, it's important to always adjust them both evenly.

The next job is to find the setting that suits your riding style and your favourite biking routes so as to achieve the right compromise between stability and responsive handling. What this means for you is that you need to alter the set-up multiple times, noting down the changes and doing a test ride each time. It's advisable to make opposing adjustments at the front and rear: lower at the front – higher at the rear, and vice versa. That way the overall centre of gravity stays at the same level and does not additionally influence how your bike handles. You will certainly be able to notice the effect that your adjustments have on handling. Each 10 mm up or down can transform a responsive motorcycle into something quite skittish, or make a stable machine really hard work to ride.

Special oil of a precise viscosity in the fork tubes and shocks damps the up and down movement of the motorcycle and prevents the springs from bouncing. We distinguish between compression damping, when the wheel if forced upwards by hitting a bump, and rebound damping, when the wheel is forced downwards by the springs. The strength of the damping effect exerted by the oil can be roughly adjusted via valves which regulate the rate of flow. If the shock only has a means of adjusting the rebound damping, any change you make will always influence the compression damping too.

The first thing you need to know is what adjustment options are actually available on your motorcycle, and where to find the adjusters. Here too, you should consult your owner's manual.

For the rebound damping, it's relatively easy to find an acceptable basic tuning with the motorcycle stationary. First press down hard on the handlebar with the brake held on. When you release the pressure, the fork must rebound without any delay, ideally a bit beyond the resting position, to which it then returns without any further bounce. If the fork rebound is noticeably sluggish, this means the fork is overdamped. Conversely, if it jumps right to the limit and even bounces several times, the fork is underdamped.

Do this test twice, first with the damper valves fully closed and then with the valves fully open. That will give you a feel for the range of adjustment. Take a look at the diagram (Graph: Effect of fork damping).

X axis) Time in seconds; Y axis) Suspension travel in mm; Line A) underdamped, Line B) optimal, Line C) overdamped,

To test the rebound damping of the shock (or twin shocks), press down hard on the tail of your motorcycle. It's OK for the shock to rebound rather more slowly than the fork (up to 1 second max.). But there must be no bounce at all. Here, too, you should check the adjustment range by carrying out the test once with the damping closed and once with it open.

You've now got a decent base setting for the rebound damping. To complete the fine tuning, you need to take your bike out on the road.

The same applies for determining the optimal compression damping. Of course, you can try out the extreme settings here too. The softer the compression damping, the more the fork will dip when you brake, or the shock will be compressed right up to the limit when you hit a pothole. For normal riding, that feels nice and comfortable on a flat road, but when you corner at speed, it will feel pretty spongy.

Conversely, a very hard setting is good for stability when you lean into the corners on the race track, for example, and will give you good feedback. But on a bumpy road, your bike will be very bouncy and, at worst, your wheels may even leave the road surface.

So when adjusting the damping, it's all about finding the compromise that best suits your riding style, the load on the bike and the sort of terrain you typically ride.  The best approach is to take your time, try out different variations and preferably concentrate on one thing at a time, i.e. only the forks or only the rear suspension.