fork oil viscosity

[docc]

I recall a link to site which had measured numerous fork oils with a viscosity measure far more accurate than SAE. Now I can't find it anywhere.

 

What was it all about?

[Guest ratchethack]

Docc, I don't recall the link you refer to above, but Pete Verdone has done a pretty comprehensive analysis here:

 

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

 

CONFESSION: I understand PART of the above, but by no means all. Wot I do understand above all is this: After trying 10w and 7.5w dino FORK OIL, looking for a lighter grade that would allow me full use of my damping adjusters on the Marz 040 fork (same as yours as you know), I finally settled on 125/150 SYNTH CARTRIDGE FORK FLUID, which has made a great improvement after the above prior progressive changes, and gives a full range of adjustability where I need it.

 

125/150 SYNTH CARTRIDGE FORK FLUID (Golden Spectro)

 

125 = 125 SUS @100F (26.26 cSt). cSt = CentiStokes, (explained at link above)

150 = Viscosity index (index of consistency of damping over large temp change)

 

BAA, TJM, & YMMV

[docc]

That's it! I thought it was Verdone and went pecking around on his sight after finding a link from a Tech Topics post, but I didn't find the chart.

 

Sending it on to a fellow with a Centauro.

 

Thanks, Ratch!

[Guest ratchethack]

Por nada, mi compadre.

 

FWIW, for practical considerations, doing the temp conversions from the above (F to C), and extrapolating between figures on Verdone's chart, Golden Spectro 125/150 SYNTH CARTRIDGE FORK FLUID is the rough equivalent of 7.5 wt. FORK OIL, in ‘cSt’, or CentiStokes, a more accurate, dynamic measure of viscosity than the SAE rating, which can be relatively misleading +/- 2-3 wt., as he points out.

 

Verdone rates Maxima 125/150 (7 wt.) Racing Fork Fluid at 26.70 cSt @ 40C

 

which is very close to

 

Golden Spectro 125/150 SYNTH CARTRIDGE FORK FLUID at 26.26 cSt @ 100F (~38C)

 

NOTE: ~2C difference between temp for the ratings

[BrianG]

I too was amazed at the difference that the change to Golden Spectro 125/150 SYNTH CARTRIDGE FORK FLUID made in the forks of the 900RR as well as the Marz Guzzi, although I never did get as low as 5w in dino oil in my experimentation.

 

The biggest difference in the Marz forks resulted from the installation of a AK-20 Axxion Cartridge Kit and 1.10 kg springs

[dlaing]

Verdone rates Maxima 125/150 (7 wt.) Racing Fork Fluid at 26.70 cSt @ 40C

 

which is very close to

 

Golden Spectro 125/150 SYNTH CARTRIDGE FORK FLUID at 26.26 cSt @ 100F (~38C)

 

NOTE: ~2C difference between temp for the ratings

Those are also very close to the Marzocchi fluid rated in that chart at 26.10 cSt @ 40C with a Viscosity Index of 150.

I think I missed the Marzocchi entry in the chart before.

It seems like better choices are the Golden Spectro Very Light and SX400, both with Viscosity Index of 400, or use what Verdone suggests, the Silkolene Pro or the Redline, with V.I.s of 372 and 389, mixed to the appropriate weight.

He also says,

"In general, Use the least viscous oil possible that produces good slow speed damping performance with the damping adjustment screws out 1 full turn from full closed. This ensures that a fair amount of fine tuning will be available for track and weather conditions."

Understanding what he means by that will really help you select the best oil.

All too often people use too thick of an oil.

The way I interpret what he is talking about, if your adjusters are dialed more than halfway out to obtain ideal damping, I think you should consider using a lighter oil/fluid, but if you close the screws to 1 full turn from fully closed and still don't get enough damping, you need a heavier oil/fluid.

I have the Ohlins so I have been using the R&T but I'd like to try mixing Redline or Silkolene Pro as Verdone suggests.

[Guest ratchethack]

It seems like better choices are the Golden Spectro Very Light and SX400, both with Viscosity Index of 400. . .

Dave, suspension fluids with VI of 400 are only required for rear shocks -- not forks.

 

Verdone (from link above):

While motorcycle rear shocks require very high VIs (over 300) to function well over such a huge temperature range, motorcycle forks and bicycles do not. Anything over 100VI will be serviceable for them.

As you no doubt know (?) Suspension damping is a very subjective thing. The kind of damping performance most desired from forks is very much dependent upon a list of considerations that are specific to every rider, including the kinds of roads ridden, the way those roads are ridden, the loads, ranges of loads, and proportions of riding time differing loads may be employed (solo, pillion, cargo), spring rates, valving design, etc.

 

There's no "better choice" for suspension fluid, just as there are no "better choices" for suspension settings that could possibly apply to every rider in every case. That's why such a wide range of options (as well as adjustment settings) are available.

 

Verdone DOES NOT suggest that a higher VI is "better" than a lower VI for all riders in all conditions. VI is an indicator of the change in viscosity of the fluid as a result of change in operating temperature.

 

With forks, for what would seem like obvious reasons, though a higher VI may be extremely important on a race track where operating temps go from ambient to relatively high, it may be of little or no importance at all to someone who rides on the road, where the range of operating temperatures is relatively low.

[dlaing]

"I suggest using either Silkolene Pro RSF (PDS)(ester) or Red Line (PDS)(polyol ester) synthetic suspension oils for front and rear suspension systems. They both have very high VI numbers and have enough of a viscosity selection to produce any mix you may need. You should, however, stay with one brand whichever way you go. I have decided to use Red Line exclusively. They range from extremely thin to extremely thick, in five different viscosities. They make the oil in nearby Benicia, CA and the oils come in really pretty colors." -- Peter Verdone

The oils he recommends have V.I.s of 372 and 389, not the low VI oils that he mentions as "serviceable" and that "function well".

Why choose an oil that only performs serviceably "well" when you can have "excellent" performance?

My riding conditions can vary from near freezing to a bit over body temperature. That is enough to make a 115VI oil like the Motul Comfort go from, oh maybe 103.8cSt at 10C to maybe 35.3cSt at 40C, while the 322VI silkolene pro RSF 7.5W might from , oh maybe 57cSt at 10C to maybe 37cSt at 40C.

There is a large difference in oil viscosities going from 10° to 40° to 100° C and the higher VIs reduce that change, so you get less fading at high temps and at low temps it functions the way you intended. Seems like a no brainer for me, unless the high VIs are reducing the lubricating ability of the fluid or have some other trade off.

I guess for people on a budget, a few dollars less for the lower VI fluid makes sense.

I can notice the difference temperature makes on my ride, and will gladly pay for the superiour high VI fluid.

[Guest ratchethack]

Why choose an oil that only performs serviceably "well" when you can have "excellent" performance?

Hooooboy, here we go. . .[sigh]. . .

 

Dave. Would you choose high-octane premium gasoline for a lawnmower that runs as well as it's ever going to run on the dino sqeezings from the cheapo pump because premium is "better"?

 

Do you know the Viscosity Index (VI) of the fork oil you're using now? You said above that "I have the Ohlins so I have been using the R&T". I presume you refer to Ohlins R&T 43, #1309-01 (??) Now of the 6 Ohlins suspension fluids listed on Verdone's large comprehensive comparison chart (linked above), four are specified as FRONT FORK FLUID, and two are specified as SHOCK ABSORBER FLUID -- but strangely enough (or not?), NONE OF THEM have any VI ratings shown whatsoever -- NOR does Ohlins list cSt numbers for ANY of their products at any temp other than 40C! Evidently Ohlins doesn't think that for practical purposes of their customers it's a SIGNIFICANT ENOUGH consideration to publish VI numbers at all -- or cSt numbers on their own suspension fluid products at temperatures they consider insignificant!

 

Now I've just gotta know. By the "logic" of wot you've just posted above, if you were to discover that the fork fluid you said you're using now isn't within the immediate vicinity of the very highest rated REAR SHOCK ABSORBER FLUID available on the VI scale, would you conclude that Ohlins is WRONG to recommend wot you've been using, and would you lose sleep until you have it drained out and replaced with SHOCK ABSORBER FLUID rated at the top of the VI chart for REAR SHOCKS, believing that doing so will transform your fork from a "serviceable" level of performance into an "excellent" level of performance for your purposes??

There is a large difference in oil viscosities going from 10° to 40° to 100° C and the higher VIs reduce that change, so you get less fading at high temps and at low temps it functions the way you intended.

Do you ride your Guzzi hard enough to get your fork up anywhere near 100C? If so, CAUTION: Don't burn your hands on your fork, Dave. Water boils at 100C. This will cook your flesh. If your fork is getting anywhere near this hot, I'd check the steering head bearings and front brake immediately, 'cause without much question, all the grease has melted and run out, and you've more'n likely boiled all the brake fluid out o' the calipers.