Fork oil rating question

[Mackers]

My Moto Guzzi Breva recommends a fork oil of FA5w or FA20w or, as alternatives Fork 5w or Fork 20w. Confused? I am.

How do these equate to SAE specifications, which I'm more used to?

 

[wileyE]

Fork oil is all over the map when it comes to true visc. One brands 10w doesn't always act the same as another brands 10w. The SAE "range" may be fine for motor oil but isn't the greatest for fork tuning. If you really want to tune you pretty much have trial and error. You can also drip test what comes out of the leg, then select something based on what you got. Here's a drip comparison of some different fluids. the s is the number of seconds it took the fluid to drip through a dampner rod size metering orifice.

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Bel-Ray High Perf. Fork Oil 10 weight 21s (same oil as 7 weight)
Bel-Ray High Perf. Fork Oil 7 weight 21s (same oil as 10 weight)
PJ1 Fork Tuner H.V.I. 5 wt. 16s
Bel-Ray High Perf. Fork Oil 5 weight 14s
Golden Spectro 85/150 2.5 wt. Very Light 13s (a petroleum/synthetic
cartridge fork oil)
Stock Paioli Fork Oil from Factory, Used 12s
Honda/Showa SS7 shock oil 5 weight 12s
Fox Racing Oil 5 weight J26 12s
Maxima Zero-Fade Light Shock Fluid 5 wt. 11s (white bottle)
Maxima High-Perf. Light Shock Fluid 5 wt. 11s (black bottle)
Stock oil out of a Boge shock 11s
Citgo Chrysler Spec 7176 ATF 41s
Valvoline Dexron III ATF 26s

Isopropyl Rubbing Alcohol 9s

 

[Pablo]

This is how Amsoil does it:

Light #5 Shock Oil

Medium #10 Shock Oil

As you can see 4.4 cSt vs. 7.3 cSt @ 100° - maybe better to compare 40°C vis. 15.7 vs. 32.1.