Fork oil change

[Andyb43]

Hi guys when have you been changing your folk oil how many miles or years? Also have you gone for a different weight oil from the manual

 

[eemsreno]

Andy
I change mine every winter about 30,000 miles a year.
I have a 2012 and I run the oil about 2 ounces less oil than called for.

 

[silvergoose]

What lead you to the reduction in fork oil? What effect have you seen, knowing the number of miles you run each year? Do you use the recommended oil weight?


Thanks and good luck, enjoy your ride reports.

 

[Chuck B]

Fork height only affects the last 20% of travel. If during your normal riding you are not using most if not all the travel available then you might consider dropping fork oil a bit. Oil doesn't compress so less oil leaves more air...air compresses. I generally won't do more than 10mm change at a time.

 

[tomatocity]

In common terms...

... would less fork oil make a softer ride?

 

[Firefight911]

Essentially, no, you will feel no difference in your ride whatsoever unless and until you are in to the last 15 percent or so of your overall fork travel.

Fork oil height affects the air gap which is also sometimes referred to as the air spring. Air, being compressible, adds compression damping in the last 15 percent of stroke. It is an exponential curve.

Example;

I'm running .90kg/mm linear springs up front. I have the correct rate for my weight. I find, through trial, that while I am riding desert trails at speed I am blowing through my stroke and operating down in the lower third of my available stroke on the front. This is due to the fact, for scenario sake, that I have become a better rider and am now attacking this trail at a rate of speed which is higher than previous runs. Standard physics at play; double the speed, four times the force, etc.

In order to offset this I swap my springs for 1.oo kg/mm linear springs. I now have moved the bulk of my stroke function to the middle third of the available stroke and have effectively compensated for the forces being applied due to the above scenario.

As a result of this change I notice that the bike is now harsh near the end of its available stroke but still compliant and composed everywhere else.

The fix? Increase my air gap by drawing off 5 to 10 mm of fluid from each fork leg. This reduces the air spring effect and "softens" the compression damping at the end of the stroke which reduces the harshness of too much compression damping only at this point in the stroke of the forks.

Fork oil height is irrelevant and has no effect everywhere else in the stroke.

Hope that helps.

Sent from my SAMSUNG-SM-G900A using Tapatalk

 

[Firefight911]

Another scenario,

You have your bike set up and functioning well and are happy with it, except during hard braking. You notice chattering and the bike feels harsh. Hard braking is hard braking that puts your forks in to that last 15 or so percent of available travel.

Reducing the fork oil height increases air gap which introduces the added compression damping further in to the stroke, thereby reducing effective compression damping during this period of time. Harshness is now reduced as a result and I reduce the harshness I was feeling.

Sent from my SAMSUNG-SM-G900A using Tapatalk

 

[silvergoose]

Thanks for the explanation, hydraulics 101. If only I could remember all that I know.


Good Luck

 

[greg the pole]

depends on where and how you ride.
I do it early..about 15-20km a year.

https://thetenerist.wordpress.com/2014/10/18/fork-rebuild-v3-0-including-fork-seal-and-bushing/