Motorcycle Suspension Set Up
Your bike was delivered from the factory with a compromise suspension set up aimed at enabling the bike to operate safely, in a variety of conditions, for a rider of approximately 75kg.
Your own weight, riding style, the condition of your local roads etc are probably a long way from what the test riders had in mind when they set your bike up.
Optimising your suspension isn’t difficult and you’ll be surprised how much better your bike will feel to ride. It’ll corner with greater precision, get the power down better, dive less under braking, and feel more stable over bumps. As an added bonus, you should also notice a significant improvement in ride quality.
Have fun and remember, if you get it wrong, you can always put everything back to standard and start again.
Step 1 Setting your preload
Preload is perhaps the most misunderstood aspect of suspension tuning. Many people think that by adjusting preload that they are stiffening or softening their suspension. This probably comes from adding preload to stop the added weight of your girlfriend/mate making the rear shock of your 125 bottom out. Winding the preload adjuster up didn’t make the spring harder, it just set the rest position of the shock’s piston higher up its travel - the result was that the shock bottomed out less.
Using the same theory, if your forks bottom out under braking, you can add more preload to set the piston higher up the tube so it has further to travel when you squeeze the lever. You could also change the spring to a harder one, or put the compression damping up to maximum, but your bike would't be very nice to ride.
The owner of shock on the left has added some preload because he is heavier than the owner of the shock on the right.
To summarise: the purpose of adjusting preload is only to set the piston in the fork/shock in the correct position.
You want to set it so that the wheels can ride over bumps, and extend down in to hollows, without the piston reaching the top or bottom of its travel.
It’s important to get the preload right, not only to stop the suspension topping/bottoming out, but also to keep the bikes geometry right. For example, if your bike doesn’t have enough preload at the back, the forks will be raked out and the steering will be slow and ponderous.
Adjusting the rear preload is often the hardest part of the process because the adjuster is usually hidden in some inaccessible place underneath the bike.
The adjuster will be stiff, there won’t be much room to manoeuvre, and your adjusting spanner will almost certainly slip at least once - to stop you skinning your knuckles, wear a thin pair of leather gloves. Unless your bike is new, the rear shock preload adjuster is also likely to be wholly/partially seized. Before you start, give it a good squirt of WD40 and leave it to soak.
For most fast road riding, your preload is in the right region if you use approximately 25-30% of your wheel travel when sitting on your bike.
Calculate the number of millimetres of travel you need by looking up the suspension travel in your bike's manual. Most modern sports bikes have a figure of around 130mm at the front and rear, which means your suspension should drop by around 40mm when you sit on your bike.
This part of the process is much easier to do if you have someone to give you a hand.
Sit on your bike and balance with your elbow against a wall. Get someone with a tape measure to see how much the bike sags from full extension.
If the suspension sags too much, add some preload to make it start from higher up. If it doesn’t sag enough, do the opposite. Keep adjusting until you get it where you need it. Do the rear first, then the front.
Remember to do this in your riding gear. It could weigh several kilos and have a significant impact on results.
Don’t forget to repeat this process if you’re loading your bike up with luggage for a long trip. It won’t matter too much on the motorway but you don’t want your bike steering like a chopper when you get to the Highlands/Pyrenees/Alps etc.
The damping is the part that stops your bike bouncing up and down like a pogo stick. Add more damping and you add more resistance to the piston moving through the oil in the forks/shock. You need to find the right balance between allowing the wheel to react to bumps and hollows, containing the weight transfer from cornering, braking and accelerating, and having a tolerable ride quality. In the next section, we'll look at what happens when the damping isn't right.
Effects of too much/too little damping
Forks - Insufficient rebound damping
- The bike will have a very supple ride at a constant speed but when you start braking and cornering, the suspension will feel soft and bouncy.
- The front tyre may chatter or bounce over high speed bumps
- There will be a general sensation of instability.
Forks - Too much rebound damping
- The ride will be harsh. It will feel as if the suspension doesn’t move when the surface is rough.
- When accelerating hard, you may feel understeer as the fork takes too long to extend and the wheel isn’t firmly in contact with the road.
- Your bike will be prone to tank-slapping.
Forks - Insufficient compression damping
- Excessive dive when the brakes are applied. The forks may bottom out resulting in a loss of suspension action (not good).
- A mushy feeling (similar to a lack of rebound damping) as there is not enough resistance to the spring being compressed.
- The rear may develop a tendency to “come round” under heavy braking due to excessive weight transfer.
Forks - Too much compression damping
- The bike will be upset by bumps encountered during braking as there is too much resistance to the spring being compressed.
- The ride will be harsh. Bigger bumps will bounce the wheel off the ground.
- There will be very little brake dive. The bike’s ride height could also be too high with the result that the bike’s steering is negatively affected.
Rear shock - Insufficient rebound damping
- A pleasant ride at constant speed but the bike will weave in bumpy corners.
- The rear wheel will chatter under hard acceleration due to lack of damping control.
Rear shock - Too much rebound damping
- Traction is reduced because the wheel can’t ride bumps due to restricted suspension movement.
- The spring can pack down from repeated shocks from the surface. This will mean slower steering because the rear of the bike will be riding lower than it should be, effectively raking the forks out.
- Lack of rear wheel control during fast corner entry.
Rear shock - Insufficient compression damping
- The bike will squat under hard acceleration and will want to run wide (understeer) on corner exit.
- The rear shock may bottom out over bumps.
- The bike will be hard to control due to excessive suspension movement.
Rear shock - Too much compression damping
- Traction from the rear will be reduced because the rear tyre can’t ride bumps and bounces off them instead.
- The ride will be harsh
- The rear will not squat under acceleration which will feel strange.
The idea is to find the right compromise between good ride quality and optimum handling. It’s worth remembering that some bikes are fitted with very hard springs as standard (e.g. the ZX10R), and Italian bikes traditionally have a much harder ride than those from Japan. More recently, bikes like the Ducati Panigale and MV Agusta F4 have been fitted with more supple suspension than earlier models. Adaptive suspension on bikes like the Panigale S and F4 RR enable the rider to select dampling characterisitcs to suit the conditions. This means you can have firm suspension for the track and softer damping for the ride home!
|The 916 has very firm suspension compared to Japanese bikes of the same era.|
A brief guide to setting up your suspension
1. Put all settings (preload, compression and rebound) back to standard. Some bikes won’t have all three adjusters. If this is the case with yours, just do what you can.
2. Head out to your favourite road (or one that’s typical of the type you like to ride on) and ride up and down it, paying close attention to how the bike feels underneath you. Ask yourself: Is there too much dive? Does it ride bumps properly or do the wheels feel like they’re being kicked into the air? Can you get the power down smoothly? As always, take care and ride to the conditions.
Because you’re on the standard damping settings, the bike should feel OK. We're now going to make it better.
3. Now try backing off the front and rear compression damping adjusters one click each from standard and ride up and down your favourite road again. The aim is to improve the ride as far as possible before if starts to adversely affect the handling and roadholding
If the bike still feels good when braking hard, and when you’re accelerating out of corners, reduce the damping by another click. If your bike dives or the suspension feels soft and bouncy, increase your compression damping.
If you're reducing the damping, keep going until the bike starts diving excessively and/or becomes bouncy when cornering. If you're increasing the damping, move up one click at a time until the ride is too harsh. At that point, revert to the previous setting - you’ve gone as far as you can.
4. Now you have sorted your compression damping. If you managed to make it a little softer, you might be able to reduce the rebound damping too.
Try one click off the forks and go for a test ride. If the forks don’t rebound too fast when you release the brakes, try another click until you start to feel a deterioration in suspension action. When you do, add a click because you’ve reached the optimum setting for you. Now turn your attention to the rear shock. Reduce rebound one click at a time until the back starts to feel bouncy. When you reach that point, add a click back in.