I have noticed for front suspension seems a little soft. So before I go and try to change the suspension settings I have always heard to make sure your suspension is in good working order including good fork oil. As far as I know my 99 F4 with 20,5XX miles on it has never had it changed. I know the fork oil, over time, degrades and causes the suspension to feel soft, but how much time? Of course if the bike is raced (mine is not) it needs to be changed out more often...but for normal everyday riding (with some aggresive riding every so often) when should it be changed? Cannot find the answer in my Haynes manual or the owners manual. Is there a "rule of thumb" out there that I do not know about?

 

My 1999 FX has done 69,900 miles and has never had it changed, and i ride it quite hard. by all means change the oil if you are looking for something in particular, but i would be inclined to try a little adjustment first. one thing at a time though!

I have read that a internal spring and oil change can transform the forks, but again it depends what you are looking for.

 

There is no interval specified for fork oil. You definately won't hurt anything putting in fresh fluid as long as you get the level right. It will come out lookingnasty...as there is a lot of aluminumchurned into the oil....and your fresh oil will look exactly the same in a week.

BelRay, PJ1, Reline make fork oil for $5-8 a quart. Racetech will sell you some reallygood fully synthetic stuff for $30 ($5 works for me)...you'll needpart of a second quart.

OEM springs do sag.....its called "taking a set"....but this does not affect their rate, only their starting length...so, screwing in your preload adjusters will temporarily compensate for it. You canbang the springs on a concrete floor and they'll expand back too. Aftermarket springs are better both in their design (wire size, number of coils and so on) as well as material., and are pre-set from the factory (the springs are compressed to "coil-up" or solid height to "set" them)