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Oil viscosities & viscosity indexes.
Suspension fluids, fork & shock absorber fluids.
Motor oils, gear oils, transmission oils, rear drive oils. 
BMW factory recommendations chart.  ZDDP??
What about GL4?  GL5?  SAE, SUS, Cst.

For: BMW and other motorcycles (and even some bicycles!).   Some information in a link for bikes and cars/trucks.  If you are trying to modify shocks or suspension by changing the oils; or, if you are curious about motor and gear oils, etc., this article may be of extra help. Note the link near the end of the article, duplicated here due to importance: (this link also has extensive brands and versions of oils and characteristics, in a charted format)
Copyright 2024, R. Fleischer

If you are interested in how oil REALLY lubricates, refer to:

Some years ago, most of the oil packaging industry changed from using SUS (Saybolt Universal Seconds) to Centistokes when describing viscosity.   I found ERRORS in Spectro Oils own charts/graphs on their website.  THEY were confusing SUS & Cst, & a few other things.  I notified Spectro of these errors, and they probably have corrected the errors.  More on this much later in this article.  The information I present to you below is the CORRECT information, AFAIK, no matter what you may find in any literature from Spectro Oils.

Spectro is not the only company that has mixed-up oil specifications, so has Castrol, just to mention a major brand amongst many others.

For Spectro products, the L. in front of the several characters following means LITER size containers; this L will be found on the containers in the product number.  Other container sizes will have different prefixes, such as the small container that has an O as prefix for the SX400 oil, below, which signifies a PINT (why not a P?, no, I don't know) container.  I list these prefixes, below, so that if you see them on your container, you will not be confused.  It is the SAME oil inside the container, no matter what prefix is in the part number.

A question mark (?), if any, means I am unsure of that value.

Note:  see and read these articles:

Fork oils:

I prefer Spectro's fork oils, or suspension fluids.  They are GOOD, have low stiction, wide temperature range (decent VI too), and the viscosities can be depended upon.

In the early Airhead days, BMW fork oil, at least for USA-sold and serviced motorcycles, was colored red & was a military hydraulic oil.   You could find its full specifications using a search engine for:  MIL-H-5606. The number has a letter at the end, and it is presently E.  To save you the trouble, the viscosity specifications for that oil are:
MINimum 4.9 Cst at 100 C
MINimum 13.2 Cst at 40 C
Maximum 600 Cst at -40 C

Due to how it is specified, & the lack of superior stiction fighters, & some other characteristics, IMO you are better off with a REAL fork-specific oil.    For the various fork oils & suspension fluids, the various manufacturer's do not agree on measuring viscosity.  Viscosity CAN be reasonably depended on, at least when the oil is brand-new, for engine & gear oils; BUT.... not so for these fork and suspension oils.  Because of that, stick with ONE manufacturer if you are trying different viscosity grades.   Except for some GS models, all the old BMW's needed a very thin oil, ~ SAE 4.    For the most part, you can translate that to modern 5 to 7-1/2 fork oils. Note the numbers above, 4.9 and 13.2, at the temperatures cited; compare those figures with YOUR manufacturer's figures; and do note where it says MINimum.   A formula to convert Cst to SUS is in this viscosity article.  HEED my remarks about sticking with ONE manufacturer.

Oil style; Spectro number and description

Cst@40C (100F)

Cst@100C (210F)

 Viscosity Index

O.SXSF  SX400 Platinum Shock & Fork Oil, SAE 2.5W




L.SFUL Ultralight shock fluid   SSU 90 ? 10.4 4.4


L.GSCF85/150, Golden Cartridge Fluid, very light.  The “85” in the model description meant 85 SUS @100F (16.9 Cst).  Later containers may be marked as “7.5” 16.9 3.5


L.F05  Fork Oil 5W, SSU 105@100F, 40.6@210F 21.6 4.4


L.GSCF125/150, Golden Cartridge Fluid, light. “125” in the model description means 125 SUS @100F. Containers may be marked “5” or Marzzochi
26.0 4.5


L.SFVL (prev. called SPL) Golden shock fluid, very light 26.4 9.9


L.F010 Fork Oil 10W, SSU 156@100F, 43.7@210F 33.3 5.3


L.F015 Fork Oil 15W, SUS 220@100F, 48@210F 47.2 6.6


Old round bottle, #3Light, SSPL series.  The bottle says:  220 SUS@100F; 85 SUS@210F 47.6 16.9


L.F020 Fork Oil 20W, SUS 335@100F, 54.1@210 72.2 8.5


NON-Spectro Oils:      
Belray fork oil 20




Harley Davidson Screaming Eagle 67.3 10.42  
Harley Davidson Type E 38 7  
Belray fork oil 10 37.4 5.8


Honda Showa SS8 Fork Oil  10W 35.48 7.38 200
Belray H.V.I. 5W shock fluid 20.75 6.67 300
Belray fork oil 5W 20.5 6.2 280
Honda Showa SS7 5W fork and shock oil 16.49 3.77 130
Yamaha 01 fork oil for Kayaba 14.57 3.45  150
Belray H.V.I. 3W shock fluid 12.6 4.1 300
Belray fork oil 2.5W 9.2 1.9 60
Maxima bicycle fork fluid 10Wt, or fork oil 10Wt 32. 6.28  
Motul fork oil, light 20. 6.  
Rockshox 5W medium, hydracoil, Torco 19.9 5.7  
Castrol fork oil 10Wt.
These figures to the RIGHT are ACTUAL TESTING on Castrol 10 wt fork oil.  Castrol has also published its own specs.  Castrol used mm squared divided by sec.  for its 'measurements'.  They published the information as:
Synthetic oil:  5.7 at 100F & 28 at 40C, VI of 151.  Castrol says 42, 7.5, & VI 150.   MY advice: disregard Castrol figures.
15. 4.


Silkolene Pro RSF 2.5Wt 14. 5.8  
Military Mil-H-5606E, the original red BMW oil (~4wt)   MIN  13.2 MIN   4.9  
Motor oil and gear oil grades are in another chart, BELOW      

In early 2010, I noticed, on two occasions, errors in data, & the chart, that had on their website. I notified Spectro Oils on these occasions, & the last error, a serious one of reversing the 40C/100C data on a comparisons of oils chart, was fixed by Spectro; upon which they sent me another thank you note.   The above data on this page comes from updated information; & this chart, clickable below in pdf format, has been corrected by Spectro themselves at my urging.

This link to a color bar chart can be useful, is easy to read.  It lists more oils than I have on this page you are now reading; I have imported it, in pdf format, into this website.  You may find the chart very useful:

Here is a link to someone else's compilation of fork oil weights:
The charting is old, but contains much more than mine, and it has the Torco figures (out of date though)

Much more information about fork oils, fork capacities, listing of fork oil viscosities, VI, tests, etc: 

The importance of proper engine oil:

Most any engine oil will work reasonably well for the Airhead engine, but there are specific areas of the engine that WILL BE DAMAGED, and perhaps expensively, if the oil is not of proper quality and that means proper additives in proper base oil that are blended by the oil makers.  The author's website that you are reading this article on,, contains several long articles on how oil really works, what oil should be used, etc.    Certain specific ingredients in the engine oil are needed to avoid $$$ problems in your BMW Airhead motorcycle.  THREE are critical.  One of them is ZDDP (or ZDP).  The amounts in commonly available automotive oils have been DEcreased, over time, in accordance with API, SAE, and oil and auto manufacturer's changes.  Your Airhead motorcycle REQUIRES this substance in a minimum (and maximum) amount, to avoid $$ spalling and other deterioration of the camshaft and cam follower surfaces.   Another ingredient is needed to be sure that under storage conditions, the cam and followers (and other items in the engine) do not have the oil dripping off and leaving the metal unprotected at engine startup.  The final ingredient of major importance is that the amount of detergents (Increasingly higher in modern car oils) should not be excessive, as that defeats BOTH long term storage metal protection AND defeats the protection of ZDDP.

Factory recommendations for engine oils:

Below is a chart, that is the best information I have from BMW.  BMW has published various such charts in its Owner's Booklets & elsewhere's for many years.  These charts have changed over the years PRIMARILY due to the better QUALITY of available oils.  BMW began recommending MULTIGRADE oils decades ago, but BMW restricted their use to, THEN, and still does, usable & safe temperature ranges.  As the years passed & oils improved, BMW expanded their recommended temperature range, but generally only for the high end temperature rating of any given multi-grade oil.  I know something about motor oils, and I think BMW's recommendations are very good.

I recommend 15W50 or 20W50 or 20W40 for most riders.  Those riders riding consistently at high speeds, or pulling trailers or sidecars, should probably only use 20W50. As a general rule I do NOT recommend single weight oils. It is my belief that they are MOSTLY only included on BMW's chart because only single weight oils are available in some countries. Otherwise, only in special circumstances of high air temperatures, and high loadings, etc., should someone use a high quality straight SAE40. This chart should be studied, particularly for the low and high temperature range for each oil.  In the mid-nineties, BMW modified their recommended oil viscosity range charts.  The below chart is the very last version for AIRHEADS.  It incorporates a number of changes.  Look closely.

BMW also sold its SuperPower oil, 5W50, for extreme conditions, -30C to +40C.   I do NOT recommend that oil unless you are starting in extremely cold weather.  BMW showed that particular oil on older charts, but changed its placement on the temperature graph, and then, finally, moved it to a simple tiny text on the same page as the chart, but not IN the chart.  You can take THAT in several ways. I take it to mean that BMW KNEW THE OIL HAD A PROBLEM!  I would NOT use that oil over that wide temperature range. In fact, I would generally avoid using that oil at all. Consider also, that such an oil and such conditions would demand early mileage oil changes!

NOTE especially that 10W50 is not recommended for over +10C (even though the oil makers try to MISinform you that it is OK); and the 15W50 is not recommended for over 30C (same sort of reasoning).  Contrast with the 20W50.   There is a real reason that certain multigrade oils are not good at higher temperatures, even though they have that top figure in their stated viscosity.  I can sum it all up rather easily:  When the top number is divided by the bottom number, and that number exceeds 2.5, the oil fails to lubricate well-enough.  THIS HAS BEEN SO FOR DECADES, AND IS SO TODAY.   It also applies to the BMW 5W50 SuperPower oil ...please do NOT purchase that oil, no matter what BMW says! ...unless the air temperature will be well-below freezing during your entire ride.

The temperatures in the chart are for the RANGE of air temperatures you will be riding in (and, to some extent the temperature of the oil/engine you are starting the engine at).  This has some broader implications than you may think.  NOTE, especially, that the chart is VERY CLEAR about the grade of oil most every rider will or should be using:  20W50 or 15W50.   Many riders use 10W40 in mild Winter conditions, but might be better for them to use 15W50.  Some riders may find themselves in countries where appropriate multigrade oils are not available.  A straight SAE30 or 40 detergent oil may be their only choice.

Article on this website dealing with cold weather starting, etc.:


SAE Motor (ENGINE) grade

 ISO grade @40C

Cst @100C (210F)




32 = 28.8 to 35.2

3.8 to 4.1


46 = 41.4 to 50.6

  4.1 to 5.6

20 68 = 61.2 to 74.8 5.6 to 9.29
30 100 = 90.0 to 110 9.3 to 12.49
40 150 = 135 to 165 12.5 to 16.29
50 220 = 198 to 242 16.3 to 21.89
60 320 = 288-352

21.9 to 26.09




ISO grade @40C

Cst @100C  (210F)

70   4.1+
75   4.1+
80 460 = 414-506 7.00 to 11.00

85 ~100 11+
90   680 = 612-748   13.5 to 23.99
140 1000 = 900-1100 24 to 40.99
250 1500 = 1350-1650 41+
  Only for quite severe conditions should you think about using over 90 weight oil. Very hot weather, high speeds, heavy loads, etc.  I am OK with synthetic oils in the transmission, but prefer dino oils, GL5, NOT GL4, in the rear drive AND transmission.  MORE info further down this article, NERDY NOTES section....  

Miscl. oil information:

Shell Rotella-T oil, 15W40:  100 Cst @40C; 15 Cst @100C; calcium 0.27%; zinc 0.135%; phosphorus 0.120%.
NOTE....this is a 2019 update!   DO NOT use Rotella T1 oil, the zinc has been overly reduced, as I expected it eventually would be. Still safe:  Chevron Delo 400.

Valvoline 4-stroke motorcycle oil,  10W40:  104.1 Cst @40C; 15.2 Cst @100C.
Valvoline 4-stroke motorcycle oil,  20W50:  169.4 Cst @40C; 18.6 Cst @100C.
Both of the above Valvoline oils: zinc 0.112%; phosphorus 0.104%; calcium 0.182%; sodium 0.052%

Valvoline VR-1 Racing Oil.  Per Valvoline themselves, ZDDP 1400 ppm zinc and 1300 ppm phosphorus.

Spectro engine oils:  All have 1800 ppm zinc & phosphorus.  AFAIK, Spectro uses both ZDDP and ZDTP, depending on synthetic, or not, or part synthetic.  Golden Spectro 4 is 30% Spectro Platinum full synthetic, and 70% Spectro 4. No matter what the container may seem to indicate, these are SG-rated oils.

Castrol's 4T oil, (and Grand Prix oil, which is the SAME OIL) in either grade 10W40 or 20W50, as appropriate to your climate, is SG rated and formulated.  Zinc component is 1100ppm in some tests, and some tests say 950; Calcium component is 1900 ppm; Phosphorus component is 1000 ppm (some tests say 750).  Viscosity is 20 Cst at 100C.  TBM is 8.

MOBIL 1 (as of March 2017 specifications):
15W50: 1200 ppm phosphorus; 1300 ppm zinc, official rating SN, A3/B3.
10W40: 1200 ppm phosphorus; 1300 ppm zinc, official rating SN, A3/B3.
10W40, Racing 4T:  1200 ppm phosphorus; 1300 ppm zinc, official rating SN, JASO MA.
V-Twin, 20W50: 1600 ppm Phosphorus; 1750 ppm zinc, official rating SJ.

BMW oil:
1.  Some longish time ago, BMW dealerships sold engine oil that was made for BMW by Spectro.  In the 20W50 grade, it had 1375 ppm of zinc; 1100 ppm of phosphorus; viscosity at 100C was 18 Cst, and the TBN was 7.5.   This oil was made for Classic K bikes, & Dealerships were to sell it for Classic K bikes AND Airheads.  MANY do not know that the very earliest of the Classic K bikes required zinc & phosphorous to SG type level amounts.   It is likely that this oil also was formulated to extend the usable life of the starter sprag clutch assembly, and for extra protection for the camshaft lobes, etc.

2.  BMW later sold a Castrol oil under the BMW HP name.  This conventional oil in 20W50 tested as follows:  1207 ppm of zinc; 1014 ppm of phosphorus; viscosity at 100C was 18.7 Cst, and the TBN was not available.  TAN was 4.12.  Viscosity at 40C was 173.5. Sulfur 14.  Calcium 636 ppm. VI was 121.

3.  I don't have the specifications on any other BMW oils.

The following is generally accepted standard information.

For MOTOR oils in STRAIGHT grades (20, 30, 40, and 50 grades), the manufacturers DO NOT HAVE TO specify at both 100C (210F) and 40C (100F).  A manufacturer MAY additionally specify at even lower temperatures.  The actual SAE official methods of specifying viscosity are rather complex, particularly for motor oils at temperature extremes, so I have not gotten into this in depth in this article, which would have needed an additional page!  It is best to avoid single grade oils.  If the country you are traveling in has nothing but single grades, then use them, in accordance with my earlier recommendations. Not having ANY oil is far worse!

SAE motor oil grades 5W and 10W usually have a LOW temperature specification. SAE 5W need not have any minimum at 0F but a maximum generally taken to be 6,000 SUS; 10W has a maximum at 0F, generally taken to be 12,000 SUS, and a minimum generally taken to be 6,000.   In older specifications, some of which may still be in use, oils under 20 weight are generally taken to NOT have a 210F rating for viscosity, except a minimum.  The specifications on oils were set up so that oils that had a W in their specification were not specified at 0F, but at 210F.  Yes, this seems to conflict with 5W, 10W (and 0W not mentioned). Someday, maybe it will all be clearly stated. But I am sure you can deduce WHY this was done, originally.

Figures are based on a VI of 96 in single grades. Because of this, and the fact that oil viscosity indexes can vary so widely, take figures that seem precise, as approximates.

For GEAR oils, SAE grades 75W, 80W, and 85W have a LOW temperature specification.  I have not listed the NON-'W" gear grades.   These have similar 100C ratings.  You have probably noticed that GEAR oils have their own viscosities, and generally a gear grade number is close to twice an engine oil grade number, for roughly the same viscosity!     There ARE straight single weight gear oils.  An example might be a straight 90 weight gear oil, which can have a specification at 210F of 75 to 120 in viscosity, SUS.

GL4?  GL5?  What's the REAL story about these?  Which are OK for your BMW transmission, driveshaft, rear drive?  What's the real information about advice not to use GL5 in old BMW transmissions and rear drives?   Read the following article.  This article is pointed towards cars and trucks and transmissions with brass synchronizers, but has some real solid information.  To summarize:  GL5 is fine for most any BMW motorcycle (and is what BMW said to use), including many of those before the Airheads.  The article has a lot of information you might like to read about your car, etc.  Disregard information you may have heard about sulfurs in GL5 being bad on Airhead rear drive brass or bronze parts.  NOT TRUE.   The bad information is a hold-over from pre-Airhead days; and, problems with manual transmission synchronizers in cars.

Below is a chart of information from  BMW;  advising changeover on early BMW bikes (pre-Airhead) from engine oil or early versions of gear oil (usually we say GL4) to GL5 hypoid rated oil.  This information came from Barrington Motor Work: Chris Betjemann's  BMW/2 Motorcycle Restoration and Service Manual (A Guide for the BMW /2 Owner/Restorer) (edited by Snowbum).

BMW AG Recommended Lubricant changeover by serial numbers. Remember, NONE of these motorcycles are Airheads!

Where R50 R60 R69
Transmission 646358 1814032 663565
Boot 646486 1814032 663565
Shaft 646486 1814032 663565
Final Drive 641986 181001 661445

For AIRHEADS, the proper gear oil is GL5 type, 80W90 or 75W90 or quite close to those viscosity ratings. Don't use 75W145, 80W140, 80W145, etc.... or any extra wide range oil, ....unless it is for quite severe use.  I advise using a petroleum oil in the rear drive.  It is a mixed bag on full synthetic gear oils for Airheads. I do think synthetics will give a longer life to the gearbox for most, but not all situations, but others may disagree.  It is safer to just use petroleum oils, and change regularly, generally at 10,000 mile intervals. There is further information here:

Note:  There is one bronze spacer (shim) in the rear drives.  BMW SPECIFIES GL5 oil.  BMW knows what is OK ....and BMW does NOT say GL4!

Converting SUS to Cst:

NOTE!   The conversion formula varies, depending on the rated SUS value, this is because of non-linear function.  Other, less accurate formulas exist, and are usually plenty good enough.

SUS between 32 and 99; use this formula:  Cst = 0.2253 x SUS - (194.4 SUS)

SUS between 100 and 240; use this formula:  Cst = 0.2193 x SUS – (134.6 SUS)

SUS greater than 240; use this formula:  Cst = SUS 4.635

Use of FULL-synthetic oils in the engine, gearbox, and rear drives:

This has always been a controversial subject.  I have changed my mind on some of these details over the years, due to changes in oils; and, due to additional information that became available.   The ENGINE will do fine on a quality petroleum oil; a quality part-synthetic oil; or, a quality full-synthetic oil (possibly some weeping or leaking at seals with a full-synthetic oil).  I have reservations about the transmission and rear drive regarding full-synthetic oils (in those two places).   The first reservation is that of seal weeping and leakage that is sometimes seen after a change to full-synthetic oil.   A more serious problem is that there are places in the transmission...and, some early rear drives....that possibly do not get adequate lubrication, particularly removal of heat from friction increases from full-synthetic oils used at splash and/or vapor lubrication places.    Another characteristic is that some full synthetic oils don't all stick that well to surfaces during cool-down/parking, especially over time.  There are differences in numerous characteristics of FULL synthetic oils that might make them rather questionable for transmission longevity...and, possibly also for the rear drive.  One such characteristic is the shearing of certain molecules from gear meshing, a well-known phenomena.   Another problem MIGHT be that transmissions without synchronizers are designed for certain spin-down rates during shifting, one reason certain lubricants and viscosity ranges are specified for them.   Even with decent additives, there MIGHT be longevity problems.    I am not the only person who thinks this way. 
I cannot recommend FULL synthetic oils for these places in common ordinary use conditions.  Extremely cold temperatures, well below what 99%+ of riders might even think about riding in, or other extreme conditions....MIGHT be another story.  I am NOT sure.

03/12/2010:  O.SXSF had two entries, with different viscosities, due to Spectro Website confusion. Obtained correct information.   ALSO re: L.SFVL, 400 VI was confirmed, so its question mark was eliminated.
03/18/2010:  Make first chart a formal TABLE, to keep things in nice order.
03/22/2010:  Greatly expand information, clean up page. Convert to tables format throughout so display in various  browsers and many screen sizes is consistent.
03/23/2010:  Add  later that same day, add more listings.
04/05/2010:  Update; and ADD ShockOilComparo bar chart in pdf format as hyperlink.
04/13/2010:  Add more oils and specifications.
11/18/2010:  Cdd Castrol 4T.
02/24/2011:  Change from 52F to 52D.
02/24/2011:  Was 52D, now 51D.
08/08/2012:  Add two links (to my articles).
08/09/2012:  Revise layout.
10/15/2012:  Add QR code, add language button, update Google Ad-Sense code.
11/07/2012:  Greatly improved table presentation; but NO technical details changed.
01/21/2014:  Remove Peter Verdone Designs hyperlink, website is NLA.
03/03/2014:  Add more information on fork oils before the chart.
08/04/2014:  Add factory recommendations chart and information, for engine oils.
01/02/2016:  Update meta codes; narrow article; left justify abp, clean up some. Add latest BMW factory information (a few small changes on engine oils).
02/05/2016:  Add link to coldstarting.htm article
04/27/2016:  Update metacodes, fix minor problems with layout, fonts, etc.
10/10/2016:  Add Mobil 1 in pertinent viscosities and types.
01/12/2017:  Revise article layout, fonts, scripts, metas, H.L.
05/25/2017:  Add Valvoline VR-1.   Almost completely eliminate the use of red color and eliminate all background color except base color. 
05/31/2017:  Recheck Mobil 1 specs.
04/05/2018:  Add link to viscosity article.
05/31/2018:  Cleanup.
08/19/2019:  Caution note on Rotella T1.
03/06/2020:  Add new Peter Verdone link.  Remove it on 08/19/2020, due to unusable display of the chart.
12/16/2022:  Storage section moved to maintenance schedule article 55....and, greatly expanded.

Copyright 2024, R. Fleischer

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Last check/edit: Tuesday, March 12, 2024