Suspension Service Intervals

[SSR Suspension]

How many times I ask this question to people and get the reply "Never" is sometimes funny, but sometimes sad. Would you never change the oil in your bikes engine? Of course you would, so why would you not have your forks serviced properly and have your shock serviced.

Get Forked
“Your Suspension needs regular maintenance to perform at its best”

Motorcycle Suspension, considered a ‘dark art’ by most motorcyclists can be simply defined as the management of weight transfer on a motorcycle chassis. Springs help support the bike and its rider whilst damping at the basic level provides a means of controlling pitch and feel.

After we set the ride height of the machine we are doing nothing more than simply controlling the transfer of load from one end of the motorcycle to the other. We do three key things when riding a motorcycle; accelerate, brake, turn. All of these things are affected by Newton’s laws of physics and all of these three things affect how the bike handles.

If we keep the concept as simple as possible and thus make the concept easy to grasp there are really only two areas we need to consider as they affect all other areas, they are both related to load transfer, essentially from the rear to the front, and the reverse, front to rear. We control this motion by controlling the suspension damping, i.e. rebound and compression. Compression, being the damping force required to allow adequate controlled bump/squat under the undulating track/road surface alongside the G-forces resultant from braking and acceleration. Rebound, the damping force required to effectively control the release of kinetic energy stored within the springs when under compression.

The primary components which make up a suspension system are all mechanical precision machined parts with varying tolerances dependent upon whether it is a mass produced factory system, or an aftermarket hand built item. Regardless of the manufacturing tolerances involved, all of these components form a system which as already described above allows the control of load transfer.

The intricacies of the system therefore allow for the damping effect to be altered to varying levels. The depending factor here is the component itself, which dictates the level of adjustability which is in built. Sports bikes and race bikes in general have full adjustment of spring preload, compression and rebound.

Basic physics states that for every action there is an equal reaction, in this case motion. Motion or movement at its very essence creates energy which then produces heat as a by-product. Heat will cause thermal expansion of materials and cause fluid viscosity to alter and this is why a cold bike may feel different to a bike that has had a good 20-minute session on track to warm up.
Looking Inside One of the most neglected and fundamentally overlooked items on a motorcycle, regardless of its use, is the servicing of the component parts. Suspension by its very nature is a moving/oil dampened mechanical part (with the exception of air forks), and like any moving part on a vehicle will need maintenance to be at its peak performance.

Items within a motorcycle suspension system are prone to wear, mainly due to movement of parts within the system, such as stanchions passing by outer legs, with the bushing being the bearing surface.

Below is a simple explanation of these parts that may be affected over time…

Bushes – these are Teflon lined, and depending on the fork’s design will depend upon their core location. These bushes provide a bearing surface for the fork stanchion and outer leg to move across each other. Shocks also utilise a bush around the shock’s core piston be it a solid piston as found for example on an Ohlins TTX/Bitubo, or a ported piston such as a Showa, KYB or Penske shock, they also have anothe bush built into the seal head body which is a guide for the shaft.

Oil – Oil otherwise known as suspension fluid will go thru heat cycles and it is important to improve performance and consistency with damping by using an oil with a high viscosity index. Viscosity index is the difference between an oil between cold and hot – manufacturers rate this at specific temperatures, to which there is an international rating system – and the higher the index the less the change in the oil’s damping performance. This is key to damping performance, particularly with shock absorbers as operating temperatures can easily reach in excess of 70 Deg.C!
Oil may also become contaminated with minuscule shavings of metal produced by a fork spring as it bows under compression inside the fork. In turn these can work their way through a fork’s valving and in some extreme cases cause a deflection within the shim-stack, potentially blocking a shim in an unwanted position which will alter the damping performance and system response.

Seals – there can be a few key problems caused by seals as they degrade, they may be damaged, they may have lost their elasticity, all of these may cause weeping of oil from the fork or the shock’s seal head. The rubber used in seals will vary greatly and as such quality will be of notable difference between brands. Another thing to consider is rubber sliding up and down the fork stanchion/shock shaft will cause stiction and believe it or not this will have some effect on the efficiency of the movement. In this case stiction is something we wish to minimise and quality seals will help diminish this effect.

Service Time - So perhaps with this more comprehensive understanding of the principles behind motorcycle suspension and the critical function of the system, how often should we be servicing the component parts? Factory teams will see their components opened up and altered in some way, shape or form most race meets, looking for vital setup changes. This could be a valving change, or some other internal change perhaps, and depending upon the component this may or may not require a full rebuild to complete the task.

Club racers and lower level racers will not have the luxury of such a service but this is not to say they are not putting their machine under equal stress/duress. Depending on who you talk to will depend upon the service schedule that is suggested and this is very aptly based upon the application the machine is used within. As a general rule a race bike should be seeing a full service on its suspension approximately every 20 hours of riding, putting this into months could mean twice per season with a service pre-season followed by a service mid-season depending upon how many hours you ride per race meet. An example of this would be that a SS600 in BSB has a ride time at each meet of approx 2.5 hours, over 11 meets in a season that total is 27.5 Hours.

A track rider would get away with the minimum of an annual service, normally conducted in the off season to allow minimum disruption to the rider’s track time. Some track riders put in serious hours over a season and with an average of 2 hours riding per track day, if you did 1 track day a month from Feb to Oct you could easily put in 18 hours of riding time.

For a road bike, there is much debate. I would say ideally annually, especially with the amount of mileage and time road riders can spend on their machines, however they are not putting the machine under the extremes of track riding or racing and thus the key component parts will not wear at such a fast rate. However, Oil deteriorates with time even not just use which many people may not realise.

If not conducted annually then Bi-Annually would be recommended for a road going bike, but in reality it is rare that a road bike has its full suspension system serviced, unless there is a visible leak which prompts the owner into action. A phrase I have always used with customers and have heard other people start to use is ‘would you never change your engine oil?’ Servicing of your motorcycles suspension really is this critical, the difference in performance between serviced and non-serviced suspension really is night and day.

A service is also not just changing fork oil and seals, have you ever seen the state of the fork fluid in a pair of forks after it has only had a seal and fluid change?

A full service is the complete strip and check of every component part from the individual shims to the pistons, top out springs and beyond, something which will not be a routine thing for your regular motorcycle mechanic nor detailed in their service schedule. Remember that motorcycle mechanics at dealership level are not trained in the intricies of suspension.

As for shock absorbers, all you are told is that the shock is gas charged and should not be attempted to be opened. This is not the case, some shocks are classed as non-rebuildable but for 90% of these shocks they are indeed rebuildable but they sometimes require extra work which only a suspension specialist can carry out.

My reccomendations are as follows:

Race - Every Season or 20 Hours (whichever comes first)
Track - Every Season
Road - Every 12-24 months
Off Road - Every 20 Hours

– Mark Standley, SSR Suspension.

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