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Wiz636

Fork/shock Oils

6 posts in this topic

I stumbled across this in another forum. I can't give a source or speak to it's accuracy but since this question seems to come up occasionally I wanted to throw it out there for whatever its worth.

oilcom1.gif

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Interesting find. Too bad they didn't include Yamaha S1 for the sake of curiosity. No Maxima fluids are listed, either, but the same info is available at their web site.

Notice that the difference in the hot/cold viscosities of most of these fluids (which is reflective of the viscosity index of the fluid) is generally always greater than the difference between a given fluid and the next one or two heavier fluids.

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Looking at the chart it appears that the lighter weight oils would perform more consistenly, flow rate wise, then the heavier weight oils and therefore the suspension wouldn't get as soft as the oil heats up.

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I find it interesting that the 100C viscosity rating between all the oils remains significantly closer than the 40C ratings (but is that something that would ever come into play?)...and I also wish that the Yamaha S1 was included...that was the first one I looked for.

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By the way, this chart is pretty good for comarison in relative terms, but does anybody know what the the y-axis values represent? Or is it the x-axis values? :thumbsup:

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There is no Y axis. The values are the viscosity in Centistokes.

http://en.wikipedia.org/wiki/Viscosity#Kinematic_viscosity:_.CE.BD

What's interesting here is that it speaks to the same issue we discussed once before, that being that the weight of oil used in a fork will change the fork's performance very little if varied within a limited range (say, from 3 to 7 or 10), since the viscosity variation of most fluids from hot to cold is greater that the difference between the oil weights themselves. That has to do with the fact the modern suspension components control pressures, and not flow rates.

And I haven't really ever thought to check at the end of a 50 mile desert run to see what the fork temperature is, but I think it would surprise me if it were to approach 100 C (212 F). That number is used because it's an oil industry standard temperature for such comparisons. 40 C is 104 F, and is probably a whole lot more normal in a fork.

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