The Confusion that is Fork Oil

Before I started researching fork oil I didn’t know much about it other than it was oily.
So I suppose you could say I knew fork oil about fork oil.

The searching started when I took my first ride after fitting my newly sealed forks.
They were stiffer than a stiff thing on a stiff day. In other word they were ‘king stiff.
I had already purchased the oil before I sent them off so Ernie put it what I had sent him.

The manufacturers W numbers bear no resemblance to the viscosity.
The Yamaha manual recommends Yamaha Suspension Oil M1 or Ohlins R&T43.
Both of which seem pretty scarce in the uk. A US site tell me that Yamaha M1 is a zero weight oil but no viscosity figures. The Ohlins site however was more helpful giving a viscosity of 19 mm2 Centistokes @ 40° C. So I had a reference point to aim for.

I contacted Opie Oils for some advice and Tim (very helpful) set about finding me some suitable oil.
His first recommendation was for any 5W oil until I pointed out that it was the viscosity that was the critical factor as the 5, 7.5, 10W etc bore no resemblance to the viscosity. Telling him my aim was a viscosity of 19. He came back again with a recommendation for Motul Light 5W Factory Line Motorcycle Fork Oil which has a viscosity of 18, so close enough for me. I then set about finding others that were in the same range so I had a choice.
Fork Oil recommendations for the Yamaha FJR 1300A
Centistokes @ 40C
Millers Suspension Oil 2.5 NT 17.2
Motul Factory Line 5W Light (Synth) 18
Motul Expert 5W Light (Semi Synth) 18
Red Line Light Weight Suspension Fluid 16
Silkolene 02 17.94

So as you can see from the figures above the W number bears no resemblance to the viscosity.
The oil I supplied to Ernie turned out to have a viscosity of 47.4, no wonder it was bloody stiff.
The right oil is on its way from Ernie. I will use Opie next time I need fork oil, Tim, you are a top man.

Dood, if'n yer in the UK, you want Rock oil!!! https://www.rockoil.co.uk/cm/products/lubricants/motorcycle

Agreed though, fork oil labeling is a black science.

Exactly right. The weight ratings printed on the bottles have little to do with the actual viscosity of the fluid in the bottle. A guy named Peter Verdone measured and charted all of the commonly available suspension fluids by actual viscosity. His data is pretty old now, but it would still be reasonable to assume that specific oils that measured a particular thickness 10 years ago would be the same today. If you google his name and "suspension fluids" you will find multiple links to the data.

FWIW - I settled on the Motul Expert Light as it was closest to OEM thinness and readily available at local bike shops.

I went with the Motul fork oil that was close to the OEM Yamaha fork oil on a chart I came across but it's not right, still a little too light. I'm probably going to spend the pennies on the Yamaha product before I ride to Austin this month for the race.

Fred W said:

Exactly right. The weight ratings printed on the bottles have little to do with the actual viscosity of the fluid in the bottle. A guy named Peter Verdone measured and charted all of the commonly available suspension fluids by actual viscosity. His data is pretty old now, but it would still be reasonable to assume that specific oils that measured a particular thickness 10 years ago would be the same today. If you google his name and "suspension fluids" you will find multiple links to the data.
FWIW - I settled on the Motul Expert Light as it was closest to OEM thinness and readily available at local bike shops.

Click to expand...

How did the Motul Expert work out for you? The expert is a semi synth and the Yamaha reccomendation is for fully syth Motul Factory Line 5W is the same viscosity as the expert and is fully synth.

Something else I dicovered whilst doing this research was to do with the mixing of oils.
The layman would think that if you take a 5W and a 10W and mix them 50/50 you would get a 7.5W but NO

During an email exchange with the nice people at Fuchs (Silkolene) the told me that to get a midway viscosity point between two oils you need to mix 2 parts heavy with 1 part light to get midway.
Here is the actual text they sent me.

Hello Rae,
Don't blend the different ranges!
I've checked with the SILKOLENE Chemists:-
To blend suspension fluids/fork oils of the same type but different viscosities.

To get a 'halfway' viscosity between 2 grades, mix 2 parts of the heavier, more viscous fluid with 1 part of the lower viscosity fluid.

Regards,

Graham Dawson

TECHNICAL SUPPORT OFFICE

FUCHS Lubricants (UK) plc
New Century Street
Stoke-on-Trent
ST1 5HU

So all you folks, me included, would have been getting it wrong.

Fred W said:

... A guy named Peter Verdone measured and charted all of the commonly available suspension fluids by actual viscosity. His data is pretty old now, but it would still be reasonable to assume that specific oils that measured a particular thickness 10 years ago would be the same today. If you google his name and "suspension fluids" you will find multiple links to the data.

Click to expand...

https://www.peterverdone.com/wiki/index.php?title=Suspension_Fluid

I usually use Bel-Ray 5W which is around halfway between the two mentioned in the original post. No issues.

Has anyone been able to ascertain the viscosity of the Yamaha M1?

https://www.shopyamaha.com/product/details/01-suspension-oil?b=Search&d=35&dealernumber=

https://www.shopyamaha.com/product/details/m1-suspension-oil?b=Search&d=35&dealernumber=

Does this help?

Both say 0 weight, whatever that means...

As already said the W number and the viscosity bear no resemblance to each other. It's the actual viscosity that is important. So I was really looking for a Centistokes number.

I did say "0 weight, whatever that means..."

Within reason, I doubt it matters that much. All of the suspension fluids have a large temperature/viscosity coefficient so specifications may overlap as a function of temperature. In centiStokes, viscosity varies by factor of ~4x between 40 °C and 100 °C for a given oil in the range I would consider. I would also expect significant viscosity change over the life of the oil as a function of contamination, oxidation and shear. That's why I picked one somewhere in the middle of the suggested range and have stayed with it. Around here, the Bel-Ray (5 wt.) is readily available, reasonably priced and has a good reputation.

Perceived differences you may encounter can be made up with fill level, pre-load, rebound and dampening settings, if the "feel" isn't right for you.

No need to make it overly complicated - I've never heard of anyone regretting their choice of fork oil on an FJR.

I chose a 10W Solkolene which had a viscosity of 47.6 (didn't know that at the time) as opposed to the Ohlins which has a viscosity of 19 so this was a massive mistake on my part. The forks were rock hard. So as long as you get somewhere close to the 19 viscosity any difference can be dialled out.

In my case I had all the setting to the softest setting and it was still rock hard, as the viscosity was so far away from the recommendation.

According to the data presented by Verdone, the Yamaha 01 fork oil is 15.6 cSt @ 40 C and 3.45 @ 100 C

The only difference a synthetic should provide is less viscosity thinning with temperature, possibly also maintaining its viscosity better with longer term use. I noticed no problem with either running the semi-synthetic Motul. I suspect that when used in a motorcycle fork the temperature never gets all that high, like it can in the confines of a shock absorber.

FWIW - both the Motul full and semi synthetic are a bit heavier than the OEM stuff, but not by a lot.

PS - silkolene and red line provide handy mixing tables for hitting specific viscosities using their products

https://www.peterverdone.com/wiki/images/c/c3/Silkolene_Mix_Chart.pdf

https://www.peterverdone.com/wiki/images/7/7f/Red_Line_Mix_Chart.pdf

Yes, The 47.6 would be a bit on the thick side for the FJR!! I'm not too surprised you had issues with it.

Fred W said:

According to the data presented by Verdone, the Yamaha 01 fork oil is 15.6 cSt @ 40 C and 3.45 @ 100 C
The only difference a synthetic should provide is less viscosity thinning with temperature, possibly also maintaining its viscosity better with longer term use. I noticed no problem with either running the semi-synthetic Motul. I suspect that when used in a motorcycle fork the temperature never gets all that high, like it can in the confines of a shock absorber.

FWIW - both the Motul full and semi synthetic are a bit heavier than the OEM stuff, but not by a lot.

PS - silkolene and red line provide handy mixing tables for hitting specific viscosities using their products

https://www.peterverdone.com/wiki/images/c/c3/Silkolene_Mix_Chart.pdf

https://www.peterverdone.com/wiki/images/7/7f/Red_Line_Mix_Chart.pdf

Click to expand...

Yes I saw the figure for the Yamaha 01 but I was really looking for viscosity figures for the Yamaha M1. I have emailed Yamaha UK for a Data spec sheet, but I won't be holding my breath for the reply. So if anyone knows the viscosity of the Yamaha M1 please speak up.

raesewell said:

Something else I dicovered whilst doing this research was to do with the mixing of oils.The layman would think that if you take a 5W and a 10W and mix them 50/50 you would get a 7.5W but NO

During an email exchange with the nice people at Fuchs (Silkolene) the told me that to get a midway viscosity point between two oils you need to mix 2 parts heavy with 1 part light to get midway.

Here is the actual text they sent me.

Hello Rae,

Don't blend the different ranges!

I've checked with the SILKOLENE Chemists:-

To blend suspension fluids/fork oils of the same type but different viscosities.

To get a 'halfway' viscosity between 2 grades, mix 2 parts of the heavier, more viscous fluid with 1 part of the lower viscosity fluid.

Regards,

Graham Dawson

TECHNICAL SUPPORT OFFICE

FUCHS Lubricants (UK) plc

New Century Street

Stoke-on-Trent

ST1 5HU

So all you folks, me included, would have been getting it wrong.

Click to expand...

A racing suspension tuner once told me to get to 7.5, they would put 10 in one fork leg and 5 in the other rather than trying to blend.

Was he Irish? or is it because it's April 1st

raesewell said:

Was he Irish? or is it because it's April 1st

Click to expand...

No, he was a tuner for multiple national championship winning teams

You'll forgive me if I don't try it eh?