Understanding Motorcycle Fork Oil And Its Relevance

Understanding Motorcycle Fork Oil And Its Relevance

Every motorcycle, at some point in its working career will consistently need replacement of consumable parts that wear out and begin to impact its overall performance. Besides hardware like spark plugs, bulbs, tyres, oil seals, brake pads, battery or cables you also have engine, brake or gear oils to contend with. 

Now, the question that comes up — where does fork oil fit in the overall equation?

As a motorcycle rider since early 70s, what I have experienced with my various rides is that motorcycles come with modern Ceriani-designed front damping rod type hydraulic forks that actually need very little maintenance when it comes to changing or replacing fork oils. 

Most Ceriani-designed forks are pre-loaded with damping and compression features designed by the manufacturer or brand and exhibit complementary performances.

For riding comfort, manufacturers design the specific damping and compression qualities of the Ceriani-designed front forks at the time of developing the motorcycle’s overall package. 

This means the damping quality of the front forks are individually calibrated in accordance to the job description of the machine being sold and usually are non-adjustable in mass production models. 

However, in some markets there are more advanced fork systems also known as active or semi-active in high-end machines that can be adjusted. These systems allow for the damping and compression ratios to be tailored according to the riders’ specific requirements.

The common factor in all motorcycles irrespective of what they have been designed to do — be it on-road commuters, sports-bikes, off-road, adventure, trails, motocross  — is to ensure top ride quality besides absorbing shocks, road imperfections before they reach the handlebar and in a way also contribute to the stability of the machine. 

This also means that the Ceriani-designed fork is a vital safety component of each machine. It doesn’t differ with upright or inverted forks as seen in machines like KTM etc. The way these forks operate efficiently is that inside each fork tube is a valve that controls the compression and rebound feature of the fork — that it when it’s going up and down, or in and out fashion. 

Oil seals inside the fork tube protect the set-up, but they also cause natural friction as a containment barrier and release some heat.

The specially composed oil inside the fork has a key role as it works directly with the valves to provide consistent damping capabilities. It is vital for the fork oil to consistently control or check the energy generated by springs and absorb the unwanted heat. When the fork oil is new, it plays its role perfectly.

Since, the fork movements are dynamic when the motorcycle is on the move, obviously there’s degradation over a period of time. And as road conditions vary, the duration related to the efficiency of the fork oil will also get impacted. How soon or late should be evident to the rider who may begin to feel the roughness of the front suspension when the motorcycle is ridden.

So what to watch out for?

For the Ceriani-designed forks to perform optimally and assuming there’s no oil seal leak, the motorcycle can be safely ridden for many thousands of trouble-free kilometres. Do remember that fork oil qualities will diminish over a period, similar to engine oil wear and tear.

If you have the manufacturer maintenance schedule that you follow, then it is worth including a mandatory fork oil change depending on the usage of your motorcycle or scooters with similar systems. 

In real-time, many riders or bike owners tend to ignore this aspect and will only address it when a distress situation arises.

When to change fork oil?

Rule of the thumb is that if you consider changing fork oil every 10,000km, then it’s an excellent decision.

If roads are good in your area, you can extend the duration to 15,000km which will still be considered good for the machine.

Here is a detailed post on how often should you change the fork oil.

By the time your machine has done 20,000 km, fork oil has lost most of its performance properties. At this juncture, there’s a good chance that the oil seals will perish and cause damage to the barrels.

Fork oil seal leaks causing friction marks on the exposed hard chromed barrel that can’t be repaired.

Do remember, you don’t have to wait for the oil seal to perish to change the fork oil. The quantity is usually less than 200cc per shock absorber and are affordable.

Fork oils are different in composition to brake or engine oils and use chemicals with anti-friction properties. 

Several friction modifiers are used to increase lubrication qualities. Most important component is the viscosity stabiliser that provides long lasting and consistent performance and response, even as the suspension heats up during use. 

Unlike engine oils that tend to foam when heated, fork oils are designed to remain cool and eliminate foaming and air entrainment properties.

Depending on what you type of 2-wheeler you ride, and how you ride it, there are a few options to choose from for replacement fork oil. 

With several product options available which usually relate to viscosity — should one opt for thicker or lighter fork oil? This may be trick question, but it’s no rocket science if you can understand some of the fundamental principles.

Let’s try and understand why fork oil viscosity is so important in the performance of front suspension in a motorcycle? 

If you explore the market and on-line resources you will discover in general, there are two types of replacement fork oils — lightweight and medium viscosity. No need to get worried or confused about deciding options. While, both types offer excellent thermal protection and damping, but do offer slightly different performance characteristics.

The damping and compression ability of the forks have been pre-determined by suspension engineers for street-going mass production motorcycles. As a result, if a single specification fork oil is offered, it is okay to go ahead with it.  

For the uninitiated, light viscosity fork oil is designed for more rapid compression and that frequently experience rebound of the front fork suspension. So, it’s perfect for off-road  riders who jump motorcycle and need safe control upon landing. 

In addition, off-road riders need quick response to every bump, log, and jump that’s encountered. Here, the mileage is not a factor, rather it’s the duration and its usage.

On the other hand, medium viscosity fork oil is a thicker and better suited to riding that requires slower compression and rebound. This quality is applicable for cruisers, street usage, mild cross-country rides or track days on a circuit.

In the market, fork oils are available from the manufacturer who sell them with correct quantity and viscosity for their branded machines as OEM supplies. 

Independent oil companies also offer fork oils for 2-wheelers like Shell, Motul, Waxpol, Deemol, Maxima among others.

Always avoid home-made or locally formulated fork oils. I have seen situations where mechanics have mixed engine oil with kerosene or mineral oil and fleeced gullible customers. Such oils is definitely a recipe for disaster for your fork and can jeopardise safety. Personally, I prefer to go by the book and opt for what the manufacturer has specified in the manual for the specific model in use.

Are there any options or does one have to stick to just one formulation for forks in advanced motorcycles that have semi-active or active systems?

Motorcycles like the Ducati Multistrada comes with Ducati Skyhook Suspension (DSS) and the BMW HP4 with Dynamic Damping Control (DDC). Actually, these represent the first production motorcycles with advanced semi-active suspension systems. 

Active suspension technology gets its origins from the automotive world and its application in high-end 2-wheelers is a recent phenomenon. 

Due to its superior performance qualities, the idea is catching up worldwide with several innovative 2-wheeler brands. These machines use magnetorheological damper systems which change their performance qualities when current is passed through them. These highly specialised oils is best sourced from the original equipment manufacturer.

For the professional user, there’s another consideration. On paper, there’s no standard viscosity index similar to engine oil. Hence, predicting the performance parameters is tought as it may vary from brand to brand. 

In such a scenario, the owner of a 2-wheeler is faced with the dilemma on how to move forward.

I think it would be wise and practical to continue with the existing brand. For the technical minded it may make sense compare shock fluid characteristics at 40ºC of various brands.

Do remember, on paper what may appear similar specs wise may not necessarily mean that the fork performance will be identical as before. The 2-wheeler motorcycle may ride harsh with minimal damping or change to a sluggish and uncomfortable ride. 

End of the day, whatever brand you opt for, your 2-wheeler should be up for your individual riding style. Factor in your body weight and any extra accessories you may have on the machine.