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What are the signs that a fork needs an oil change?

I'm asking this because lately my RS Revelation (1yo) seems stiff. I checked the sag and found I should increase it... so I did, but it's still using almost the same amount of travel (I check the o-ring at the end of a ride). Moreover, on rough terrain (gravel), I feel an incredible amount of vibrations that hurt my fingers.

Are these the signs? (in other words: will an oil change solve these problems?)

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2 Answers

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Over time forks become less responsive (move slower basically), but as this effect happens over the course of 12-18 months (the usual fork oil and seal lifetime), it's difficult to notice as you just get used to it. So most fork manufacturers tell you to change it after so many miles.

This responsiveness loss happens for a couple of reasons on different types of damping systems, on mine (Boxxers) it's because of pollutants in the oil itself - 'dust' from the bushes, dirt, seal flake off, etc.

You can get a rough idea of the state of your fork oil just by looking at it, new stuff is clear tinted yellow. I've seen fork oil come out looking like mercury from the sheer quantity of bushing dust in it...

Technically you only need to change seals once they start leaking oil, but of course that usually means that they've already failed their job - if you ride a lot in dirty conditions (which you should be!) they want changing every year.

Bushes only need changing once there's excessive play between your stanchions and sliders, this usually takes years but you can test the same way you would for testing a headset.

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Oil itself can degrade, plus the pollutants this answer mentions, as oil degrades and contaminates it changes its viscosity and other properties. Many suspension designs rely on these properties to achieve the ride quality they provide. Changing the oil should be not an expensive service a your local bike shop. – Jahaziel Jan 24 '12 at 17:57
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I usually only replace the oil when the level gets low (which should only happen if a seal is leaking), although I think many manufacturers do recommend changing it periodically.

Typically the only regular maintenance I do to my forks, other than inspecting the oil level, is to re-grease the stanchions. A lot of forks have a grease port on the outside that you can inject some grease through, or I will drop off the legs and clean and re-grease the stanchions, using some good fork grease.

I would look up the service manual for your fork too. It probably makes some suggestions as to what the maintenance schedule should be.

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