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Oil viscosities & viscosity indexes.
Suspension fluids, fork and shock absorber fluids.
Motor oils, gear oils, transmission oils, rear drive oils. 
BMW factory recommendations chart.
What about GL4?  GL5?
SAE, SUS, Cst.
Some info on ZDDP content.
Long term storage.

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.
Copyright, 2014, 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 and Cst, and a few other things.  In February of 2010 I notified Spectro of these errors, and they "should" have corrected them.  More on this much later in this article.  The information I present to you below is the CORRECT information, as far as I know, no matter what you may find in 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, and this L will be found on the containers as 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 was red, and was really a military hydraulic oil.   You could find its full specifications using a search engine for:  MIL-H-5606E.  Just 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, and the lack of superior stiction fighters, and some other characteristics, IMO you are better off with a REAL fork oil....especially a full synthetic fork oil.    For the various fork oils and suspension fluids, the various manufacturer's do not agree on measuring viscosity.  Viscosity CAN be depended on, at least when the oil is brand-new, for engine and gear oils, 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, roughly 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.   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. The 125 in the model description meant 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         100
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      15.    4.

To the left is ACTUAL testing
on Castrol 10 wt fork oil. 
Castrol has 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.    For 10wt oil listed
in the left columns, they say 42,
7.5, & VI 150.  For just "Fork Oil" they say
15, 4.0, & 150. MY advice: disregard Castrol figures.

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 the data, and the chart, that had on their website. I notified Spectro Oils on these occasions, and 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; and this chart, clickable below in pdf format, has been corrected by Spectro themselves at my urging.

This chart can be useful, lists more oils than I have on this page you are now reading; and gives a colored bar-chart appearance, which may be easier for you to use.  I have imported it, in pdf format, into this website.
You may find that chart very useful:


Factory recommendations:

Just below is a chart, that is the best information I have from BMW.  BMW has published such charts in its Owner's Booklets, and elsewhere's, for many years.  These charts have changed over the years PRIMARILY due to the better specifications of available oils. 

BMW began recommending MULTIGRADE oils decades ago, but BMW restricted their use to usable/safe temperature range back then.  As the years passed and oils improved, BMW expanded their recommended temperature range, but only for the high end temperature of any given multigrade oil.

In the chart below, BMW listed its Super Power oil.  I do not recommend it; unless you plan on starting your bike in extremely cold weather, consistently below freezing.  I recommend 15W50 or 20W50 for most riders.  Those riders riding consistently at high speeds, or pulling trailers or sidecars, should probably use a 20W50.

In the mid-nineties, BMW modified the below chart, and no longer recommended the SAE 10W40 or SAE 10W30 to be OK down to -30C; moving that point back up to -20C.  How many of you ride in that cold of weather?



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 = 90.0-110                 9.3 to 12.49
                      40        150  = 135 - 165            12.5 to 16.29
                      50        220 = 198-242            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     68 = 460 = 414-506

            7.00 to 11.00

                       85              ~100                  11+
                       90       220 =680 = 612-748             13.5 to 23.99
                     140    ~500 = 1000 = 900-1100             24 to 40.99
                     250    1500 = 1350-1650                   41+
  Only for severe conditions should you even think about using over 90 weight oil.  I am OK with synthetic oils in the transmission, but prefer dino oils, GL5, NOT GL4, in the rear drive.  MORE info further down this article, NERDY NOTES section....  



LONG TERM STORAGE:  once in a while, I have someone inquire about what type of oil to put in the engine for extreme long term storage. This is not just Winter Storage, but for YEARS.   I recommend a special oil sold under the Joe Gibbs label, called Hot Rod Oil.


Miscl. oil information:

Shell Rotella-T oil in 15W40:  100 Cst @40C; 15 Cst @100C; calcium 0.27%; zinc 0.135%;
      phosphorus 0.120%.

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

Spectro engine oils:  All have 1800 ppm zinc and 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.

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.

BMW oil:
1.  Some time ago BMW sold an engine oil, 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, and sold for them AND Airheads.  Earliest
     of the Classic K bikes required zinc and phosphorous to SG type level amounts.
2.  BMW 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, for 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! 

SAE motor oil grades 5W and 10W 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 any 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.

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 oil grades: 
SAE grades 75W, 80W, and 85 W 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.  This 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 non-use of 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, including many of those before the Airheads.
It has a lot of information you might like to read about your car, etc.

Another viewpoint:
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.
Here is the information, in case you want it:
Below charts where BMW advised about the changeover on early BMW bikes from engine oil or early versions of gear oil (usually we say GL4) to GL5 hypoid rated oil.
From Barrington Motor Work: Chris Betjemann's
BMW/2 Motorcycle Restoration and Service Manual
(A Guide for the BMW /2 Owner/Restorer)

BMW AG Recommended Lubricant changeover: oil to hypoid
(By Model and Serial number/engine/frame No.:)
                           R50                     R60                              R69
Trans             646358              1814032                        663565
Boot               646 486             1814032                             "
Shaft                   "                          "                                    "
Final Drive    641 986            1810001                        661445

For AIRHEADS, the proper gear oil is GL5 type, 80W90 or 75W90 or quite close to those ratings. Don't use 75W145 or any extra wide range oil, unless it is super severe use.  I advise using a petroleum oil in the rear drive.  It is a mixed bag on full synthetic gear oils for Airheads.  It is SAFER to just use petroleum oils, and change regularly.
There is further information here:

Note that 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.
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


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......and convert to tables format
                      throughout so display in various  browsers and many screen sizes is consistent.
03/23/2010:   Add hyperlink:
                     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:   add 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.

Copyright, 2014, R. Fleischer

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