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Thread: Motorcycle Fork Oils

  1. #1
    Rusted princesirohi's Avatar
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    Icon2 Motorcycle Fork Oils

    Fork Oils

    Since very less information is available on xbhp about fork oils, I am starting this new thread. Recently I had to change the fork oil of my P200NS, and started my search to find the best possible oil for my bike’s forks, unfortunately I was shocked when I found out that very little information is available on fork oils. Everything, from the grade mentioned in service manual, to service center recommendation, to grades mentioned on fork oils available in market, to biker buddies advise was so confusing and dangerous mix of half correct half incorrect information, that I decided to fully understand the topic and decode it completely.

    Untill now, like most others, I was happy with whatever my mechanic used to put in my bike’s fork, which was mostly one of these brands --Veedol / Gulf / Bosch / Endurance and/or more recently Motul. It was infact Motul, which started my thought process in this direction, since they have two options available in India (5wt & 20wt) and four internationally (5wt, 10wt, 15wt & 20wt)

    The following information is a result of internet research, discussion with friends, mechanics & authorized service centers.

    Motorcycle Forks:
    First let us understand the working of motorcycle forks. A fork has two main components (w.r.t. the current discussion) i.e. spring and fork oil. Spring basically provides compression and rebound whenever our bike hits a pothole. The job of fork oil is to provide damping, it provides both compression and rebound damping, i.e. viscosity and quantity of oil (along with a lot of other design factors, ignored for simplicity) determines the rate of compression and rebound. In simple terms, how fast the front fork depress on hitting an obstacle and how fast it bounce back is decided by oil. It does so by moving the oil / fluid from one side to other through a small orifice or valve.

    Primary Function of Fork Oil:
    So, the primary function of fork oil is to provide damping and not lubrication, ofcourse it lubricates some of the internal moving parts, but that is its secondary function. For this reason, the fork oil grade will be determined by the damping requirements and not by its lubricating requirements.

    Fork Oil / Suspension Fluid / Hydraulic Oil:
    Since the primary function of fork oil is to provide damping rather than lubrication, in terms of its character, it is much nearer to Hydraulic Oil/Fluid as compared to lubricating oils/engine oils/gear oils etc. This differentiation is very important, and will be discussed later on. A more correct nomenclature for Fork Oil is “Suspension Fluid” or “Hydraulic Fluid”, however for the sake of general understanding we will stick to “Fork Oil”.


    Now, the next thing we need to know is various grades of fork oils, and to understand that we have to understand viscosity, its types and its units of measurement.

    At this point the discussion will get a bit technical, but it is required to fully understand the fork oil grades. You need to have some understanding of the terms “absolute” and “relative”. You also need to have knowledge of S.I. units and C.G.S / F.P.S. system of measurement.

    Viscosity: It is the resistance offered by a fluid when it is made to flow.

    Dynamic Viscosity: It is the “absolute viscosity” of a fluid i.e. resistance of a fluid to flow.

    S.I. Unit of measurement for dynamic viscosity is N.s/m2 or Pa.s or Kg/m.s
    C.G.S. Unit of measurement for dynamic viscosity is g/cm.s or dyne.cm/s2 or poise (p)
    1 centipoise (cP) = 0.01 poise = 0.01 g/cm.s = 0.001 Pa.s = 0.001 N.s/m2

    Kinematic Viscosity: It is the ratio of dynamic viscosity to density of fluid.

    S.I. Unit of kinematic viscosity is m2/s
    C.G.S. Unit of kinematic viscosity is Stokes (St)
    1 centistokes (cSt) = 0.01 St = 0.000001 m2/s

    Saybolt Universal Seconds (SUS) / Saybolt Seconds Universal (SSU):
    Viscosity in SSU at temperature ‘t’ (Deg. F) = (1+0.000061(t-100))*4.632*(KV in cSt)

    Viscosity Index (VI): It is the change in viscosity from 40 oC (104 oF) to 100 oC (212 oF). It tells us, how stable the oil is across temperature range. Higher the VI, better it is.

    VI starts from 0 and goes to more than 400. A VI of 150 is good enough for Fork Oils. Higher the VI rating, better the oil.


    Now, we will look at various grading systems available for Fork Oils—

    SAE Engine Oil Grading System: SAE has a grading system for Engine Oils as mentioned in standard J300. It has 11 different viscosity grades. Grades - 0W, 5W, 10W, 15W, 20W, 25W are winter grades i.e. their viscosities are mentioned at lower temperatures (Cold temperatures) and Grades – 20, 30, 40, 50, 60 are hot viscosity grades i.e. their viscosities are mentioned at a temperature of 100 & 150 degree celcius. The various viscosity ratings for all the grades according to standard J300 of SAE are --


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    Now, there can be single grade and multigrade oils, as we all know. A single grade oil has to meet its viscosity rating as mentioned above, a multigrade oil has to meet both the low temperature and high temperature viscosity ratings.

    SAE Gear Oil Grading System: SAE has a separate grading system for gear oils as mentioned in standard J306. This grading is as follows—

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    Saybolt Scale: This grading system ranks the viscosity in SSU at 100 Degree Celsius temperature. This grading system is not used now.

    ISO Grading System: These grades are basically used for hydraulic oils. These are as follows—


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    Now, after studying the basics of viscosity and various grading systems, and knowing that fork oil is basically used for its hydraulic effect rather than lubricating effect, we can say that grading of fork oil should be as per the grading system for hydraulic oils i.e. ISO Grade. One more reason to favour ISO grading system is the fact that this system specifies exact viscosity values required at a particular temperature, rather than say SAE system, which specifies a range of viscosity.

    However, reality is very far from the above logic, ofcourse .... not all things in this world or life are logical.

    So, go and check the service manual of your bike, to know the exact grade of oil for your bike’s front fork, for example – I have a Pulsar 200NS, and its service manual says –> SAE-10W20. Now why is it specified in SAE Engine Oil Grade, rather than by a Hydraulic Oil Grade, is a mystery I would like to ask one day to Bajaj guys. Whatever brand of bike you own, chances are that your fork oil grade will be mentioned in service manual in terms of SAE Engine Oil Grade.

    So, what is the big fuss about grades, if industry uses a particular grading system, let them use it. Just buy the matching grade fork oil and use it. Right. …. Wrong.

    Read on…

    First of all, SAE system specifies a range of viscosity for a particular grade, which is perfectly fine for engine oils, where lubrication is the prime concern. In a fork, we are using the oil for damping purpose and slight change in viscosity will cause a change in your fork’s performance in terms of change in compression and rebound damping. So you need exact viscosity rating.

    Second, one more important parameter in case of fork oils is Viscosity Index (VI), which specifies the change in viscosity as the oil gets heated up, coz when we ride our motorcycle, the fork keeps on working, moving up and down, and pumping oil etc and the oil gets heated up. If the VI of the fork oil is poor, it will get thinner and will not give as much damping as desired. Ofcourse unlike engine oils, fork oil will not heat up in 5-10 mins, instead it take around 30 mins of riding on average quality roads to heat up, but hey, you do ride more than 30 mins at a stretch. So VI is an important parameter of fork oil.

    Third and most amusing thing. Armed with all this knowledge you head out to nearest oil shop to buy the best fork oil for your bike, only to find that fork oils grades mentioned on bottles do not match with anything we have learned so far.

    Read on …..

    Most of the fork oils available in market are labeled as either light/medium/heavy or graded by a system of grading called as “weight” of oil, and denoted by either ‘W’ or ‘wt.’ Such as –


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    So, what is this ‘weight’ of an oil, it seems that fork oil manufacturers have devised a hypothetical and fancy way of grading their oil, which does not corresponds to any of the established standards of oil grades. They took the SSU/VI measurements and converted it to weight based on SAE Engine oil grades.

    So, for example, a 5 weight fork oil denoted as ‘5W’ or ‘5wt.’ will have a kinematic viscosity of 3.8 cSt (at 100 Degree Celcius) or more. Meaning, it can have a viscosity of 3.8 or 3.9 or 4.0 or 4.1 or anything above 3.8 and this is exactly the case, and X branded 5W fork oil will have different viscosity than a Y branded 5W fork oil. An oil of viscosity 3.8 and a different oil of viscosity say 4.0 can both be branded under same “weight” category i.e. 5W, and in terms of performance, they both will be significantly different.

    Infact, if oil manufacturers would have used this method of SAE equivalence only, it would have been still ok, as you can make out the range of viscosity for a particular label of oil, BUT they have gone a step ahead and devised intermediate categories like 2.5, 3.5, 7, 7.5 etc, which do not even exist in SAE scale. Infact, if you visit the links given at the end of this article, you can easily find out that sometimes a 7W oil of one manufacturer is actually of equal viscosity or thinner (less viscous) than a 5W oil of another manufacturer, and this is not only confusing, but actually a wrong way of grading. But that’s the way it is.

    Somewhat like “Pepsodent is 10X better than Colgate”…Scale Unknown …

    So, what are we supposed to do?

    Find out the stock fork oil grade required in your bike and find out the viscosity ratings of oils available in market and decide “intelligently”…. Easy….hmmmmmmnnnn…….

    I have made a comparison of probably all the fork oils available in India -->


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    The above table should help you in finding your bike’s most suited fork oil.

    My bike (P200NS) requires a fork oil of SAE 10W20 Grade, that means the oil should have a viscosity of 5.6 – 9.3 cSt at 100 Deg. C., so I should use HP Shock Absorber Oil GB or Gulf Fork Oil 10W or Bosch Fork Oil or Shell Advance Fork 10/15W. Lets see, I will change the fork oil on Saturday and update next week.

    One more thing, just like engine oils, fork oils also come in Mineral, Semi-Synthetic & Fully Synthetic, although it is seldom mentioned on bottle.



    -----------------------------------------------------------------------------------------------------------------------------------------
    Disclaimer: Some of the images are downloaded from various websites, and copyright if any is duly acknowledged.
    ------------------------------------------------------------------------------------------------------------------------------------------

    Some usefull links -->>

    Ever wonder about fork oil? - ADVrider
    Ride Reports and Other Drivel: The Secret World Of Fork Oil
    Suspension Fluid - Pvdwiki
    Fork oil weights
    Marketing, Public Relations & Press Release Communications by MediaTurbo
    Viscosity index - Wikipedia, the free encyclopedia
    Motor oil - Wikipedia, the free encyclopedia
    SAE J306
    SAE J300
    Viscosity - Wikipedia, the free encyclopedia
    Dynamic, Absolute and Kinematic Viscosity
    Comparative Oil Weights Table - Transmoto
    http://www.vstrom.info/Smf/index.php....0;attach=2125
    ISO Grade Oil Properties
    Viscosity Converting Chart
    Fork Oil Expert Heavy 20W - Motul
    http://www.quickfds.com/out/16851-69...117-010072.pdf
    https://www.amsoil.com/shop/by-produ...oil/?zo=506774
    Bosch - Front Fork Oil
    http://67.192.83.106/gulfoilsearch/D...122905.pdf&t=P
    Gulf :: Lubricant Products
    Two Wheeler Oils :: VEEDOL FRONT FORK OIL
    http://www.epc.shell.com/Docs/GPCDOC...62025_1A0F.pdf
    http://www.hindustanpetroleum.com/do...lityFluids.pdf
    ---------------------------------------------------------------------------------------------------------------------------------------------

    Hope, you will find it usefull.
    Attached Images Attached Images  

  2. #2
    Moderator The Monk's Avatar
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    Default Re: Motorcycle Fork Oils

    Thread Approved

    Thanks a ton for starting this thread, can't find a similar pre-existing thread. I am sure people would find it very useful as a one stop place for all information.

    Cheers
    Biking is not about what you have between your legs, its all about how well you use it!!!!!!!

    Give your details here if you want to help your fellow xBhpian stranded in your city

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  3. #3
    Rusted nadz11.ns's Avatar
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    Default Re: Motorcycle Fork Oils

    Thanks a ton @princesirohi..

    Actually not many (including me) never gave much thought to fork oils. Used whatever svc or local mechanics used.
    Would be reading the provided links today for better understanding.
    princesirohi likes this.

    Ride safe and have fun.
    Regards
    Nadeem


  4. #4
    Rusted princesirohi's Avatar
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    Default Re: Motorcycle Fork Oils

    @The Monk & @psr ji : thanks for liking it.Hope, it will help fellow bikers.

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    Moderator Divya Sharan's Avatar
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    Default Re: Motorcycle Fork Oils

    Wow! Read it twice, couldn't still get a few terms. A Wikipedia search would help me understand better, but an awesome detailed in depth research.

    Sent from my GT-I8350 using Tapatalk

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    Rusted RSM2852's Avatar
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    Default Re: Motorcycle Fork Oils

    For a moment i thought that i am back at the chemistry lecture in my college.Thanks a lot@Princesirohi,this thread is one of the most informative ones.

    "On four wheels you travel and on two wheels you explore."
    Rahul S Moshal 'Le'
    princesirohi likes this.

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    Rusted princesirohi's Avatar
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    Default Re: Motorcycle Fork Oils

    So, i changed the fork oil.

    My service center used "HP Enklo 68" oil.

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    It is a Hydraulic Oil of ISO68 Grade.

    Viscosity @ 40 Deg. C. = 68 cSt
    Viscosity @ 100 Deg. C. = 8.7 cSt
    Vicosity Index (VI) = 90

    So, it is quite heavy oil (High Viscosity) and provides heavy damping, probably the only other fork oil available in India of viscosity higher than this is Motul 20W.

    Apart from this, I have come to know through friends and mechanics that Mak & Castrol fork oil are also available in india, although it is not listed on respective company websites. will do some more research and come back again.

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    Rusted princesirohi's Avatar
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    Default Re: Motorcycle Fork Oils

    i have requested viscosity related information from all the fork oil manufacturers in india, who do not display this on website.

    brands like - Veedol, Castrol, MAK. Waxpol.

    I have also requested Endurance to specify which is the recommended grade and brand of oil for the forks manufactures by them.

    Till Now, i have only received information from Castrol.

    Castrol Fork Oil 20W is available in India. Its tech, specs->

    Viscosity @ 40 Deg. Celcius = 68 cSt

    Viscosity @ 100 Deg. Celcius = 11.2 cSt

    Viscosity Index (VI) = 150.

    Will update the original sheet once i get info from all the companies.

  9. #9
    Rusted princesirohi's Avatar
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    Default Re: Motorcycle Fork Oils

    I did not like HP Enklo 68 oil, it is too much viscous and gives too much damping, resulting in hard suspension.

    Removed it and put Bajaj Fork oil, it is bsically manufactured by HP and packaged for Bajaj, with bajaj branding, just like bajaj dts-i oil.

    however, unlike the dts-i oil, i found the quality of this oil is very good. it is very thin, i.e. less viscous, almost transparent, just like water. Now, my bike's front fork are back to normal.

    there is no grade mentioned on the bottle, but since its written in service manual that recomended grade is 10W20, i think this is a 10W20 oil. also, i think this is the same oil as HP Shock Absorber oil E, since it is approved by endurance and bajaj forks are made by endurance.

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    Updating the chart in first post.

  10. #10
    Keyboard Warrior chaosaddict's Avatar
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    Default Re: Motorcycle Fork Oils

    Commendable feat Sirji! I just understood what actually the SVC did with my fork sometime back.
    princesirohi and Ravikiran like this.
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