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Discussion Starter · #1 · (Edited)
Owning two highly-tunable Foes F1-XL forks I've become a bit of a fork tuner, so I thought I'd share some oil viscosity info with you DIY guys. You can't just grab a bottle of X-weight oil and actually get what you want, since the manufacturers are all over the map when it comes to weights. So I built a chart of viscosities for several of the major brands:

Chart of fork oil viscosity.

If anyone has any additional oil specification data, please pass it along and I'll add it to the chart.
 

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1000-oaks said:
Owning two highly-tunable Foes F1-XL forks I've become a bit of a fork tuner, so I thought I'd share some viscosity info for other DIY guys. You really can't just grab a bottle of X-weight oil and get what you want, since the manufacturers are all over the map when it comes to weights. So here's a chart of viscosities for a few of the major brands.

Brand
Redline

Redline

Torco RFF

Golden Spectro
Torco RFF

Maxima

Redline

Torco RFF
Silkolene

Golden Spectro
Redline
Fox Fluid
Silkolene

Torco RFF

Maxima

Torco RFF
Silkolene

Maxima

Redline
Silkolene
Maxima
Labeled Weight
Like Water (1.4)
ExtraLight (2.5)
5
Ultra Light 85/125
7
5
LightWeight (5)
10
5
Very Light 125/150
Medium (10)
7
10W-20
15
10
20
15W-20
15
Heavy (15/20)
20W-20
20
Viscosity at 40C in cSt
5.5

9.8

10.75

16
16.1

16.2

18.4

19.9
22
26.1

30.4
31.82
32

33

37.4

43.9
46

47.1

66.8
68

71.1


Viscosity Index

344

402
?
?
?
202
407
?
106
?
369
300
169
?
182
?
153
151

256
101

151

The viscosity index reflects how well an oil retains its viscosity at various temperatures, so the higher the index the better. For some reason Torco seems to label their oil at double the weight it really is. (RockShox oil is alledgedly repackaged Torco but with the correct weight on the label.)
I use the information from this site:

http://www.peterverdonedesigns.com/bikesuspension.htm

Fox uses Torco RSF not RFF.
 

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1000-oaks said:
I just completely redid the list (and made it a printable size), and many of the figures I pulled off manufacturers spec sheets conflicted with the pvd data. Personally I'm leaning toward the manufacturer's data, and will continue updating the list.
Excellent. I'm struggling with one oil that I use because the manufacturer appears to have pulled the spec sheet because it is a discontinued product. The ideal job would be to maintain the list with hyperlinks to the manufacturers spec sheets.
 

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www.derbyrims.com
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Atf?

Interesting chart. What's the viscocity weight of ATF? (maybe each brand is different, but is there a short range of real weights?)

Back in the late '90's or Y2K there was an MTBR shocks-forum trend I followed of using ATF (auto-transmission fluid) instead of Marzocchi oil, rumored to be Golden-Spectro 7.5 wt, in their Z1 forks. ATF was rumored to have better anti-foaming properties than fork oil, and a $1.50 quart bottle of ATF was of course much cheaper than $20 for a pint of Marzocchi's oil. Compared to the Marzocchi "7.5 wt" I found I had to increase the Z1 fork damper aduster in slighlty towards the firmer direction to keep the same damping feel after changing to ATF.

ATF was rumored to be 10wt but it acted like it was lighter than the Marzocchi oil's "7.5 wt". Maybe ATF is really close to 10wt but Marzocchi's fork oil is really much heavier at 26.1 wt as you list.

Thanks for posting all the research.
 

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"El Whatever"
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derby said:
ATF was rumored to have better anti-foaming properties than fork oil, and a $1.50 quart bottle of ATF was of course much cheaper than $20 for a pint of Marzocchi's oil. Compared to the Marzocchi "7.5 wt" I found I had to increase the Z1 fork damper aduster in slighlty towards the firmer direction to keep the same damping feel after changing to ATF.

ATF was rumored to be 10wt but it acted like it was lighter than the Marzocchi oil's "7.5 wt". Maybe ATF is really close to 10wt but Marzocchi's fork oil is really much heavier at 26.1 wt as you list.

Thanks for posting all the research.
I'm not sure about that, Ray.

To top up the oil in my old auto tranny and to add oil to forks, I pull the oil from the bottle with a syringe and piece of tubing.

I don't know how scientific is this, but I see that the ATF foams in the syringe while the Fork fluid (Yamalube, Motul, Fox, Zoke) doesn't while you suck it from the bottle.

Maybe that's why it felt like being lighter than Zoke oil... because it was foaming.
 

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Magurified
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I used Amsoil ATF in one pair of forks - It's 40C viscosity is 32.4. However, it seems thinner at low temps than other ATFs because it is fully synthetic. Esso Dexron III fluid is 37.

The forks where I used the amsoil called for an SAE 20 fluid, but I wanted to increase the speed of compression and the ATF was about right.
 

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Warp said:
I'm not sure about that, Ray.

To top up the oil in my old auto tranny and to add oil to forks, I pull the oil from the bottle with a syringe and piece of tubing.

I don't know how scientific is this, but I see that the ATF foams in the syringe while the Fork fluid (Yamalube, Motul, Fox, Zoke) doesn't while you suck it from the bottle.

Maybe that's why it felt like being lighter than Zoke oil... because it was foaming.
Could be. I joked back then those early Z1 orifice damper forks must have used increased foaming at higher speeds to avoid spiking. Maybe that was really true! :thumbsup:
 

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Warp said:
I'm not sure about that, Ray.

To top up the oil in my old auto tranny and to add oil to forks, I pull the oil from the bottle with a syringe and piece of tubing.

I don't know how scientific is this, but I see that the ATF foams in the syringe while the Fork fluid (Yamalube, Motul, Fox, Zoke) doesn't while you suck it from the bottle.

Maybe that's why it felt like being lighter than Zoke oil... because it was foaming.
Were you drawing the atf at operating temps and pressures it was designed for?
 

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"El Whatever"
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junktrunk said:
Were you drawing the atf at operating temps and pressures it was designed for?
Good point... no.

I was just sucking it with a syringe at atm pressure and ambient temp. Much like it would work on a bike fork.

ATF in the car indeed would run hotter and pressurized by the pump.
 
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