well, theres what the manual says, which is just enough to prevent things from corroding.. and then theres max performance, then theres somewhere in between where most human beings are.
every 5k is what ppl like the racetech guys, dave moss, etc will tell you, and they often do. meanwhile ive seen with my eyeballs forks that got serviced for the very first time at like 22k miles and the insides looked a bit gross. thats alot of crap floating around in that oil, lemme tell ya.
this thing that some crews do with the sand paper on the fork tubes, claiming that the super fine little scratches it makes holding oil.. im not sold on that. but one thing is for sure, waiting anywhere near recommended intervals from the manual probly isnt best based on the simple fact that the oil gets sketchy long before then. 15k miles max id say is safe but thats assuming no track days and no hard braking which is hard enough to near-bottom the forks.
Point(s) taken. To address them in reverse, lol, the reasoning behind knocking down the scratches on the inner chrome tube is to smooth out any minor nicks caused by small road debris (kicked up by the front tire, or from a vehicle just ahead), that could possibly cut the fork seals. I've seen ultra fine-grit sandpaper, steel wool, emery cloth and even small oil stones used for this. Any damage deeper than that will require fork disassembly and seal replacement.
If you clicked on the link I provided when I replied to 8thvision
, you would have seen that it was from an Motorcyclistonline article written by Mr. Moss himself. You are absolutely correct about fork oil becoming nasty, and it doesn't even need to be a sportbike...think about how much stroke a motocross or ADV bike's fork has. As stated in the article, the mere action of the springs rubbing the insides of the fork tubes results in oil contamination that, left unchecked, can possibly affect your valving. But that's in extreme cases of neglect.
With the exceptions of the times he's unavailable, Dave is pretty much my go-to guy when it comes to tuning my suspension, and has been for years. I've never heard him mention the 5k figure to me; at the very least 7k on a streetbike is more realistic. Funny you mention 22k miles...that's about the mileage on my 2011 750 trackbike had when I bought it as a salvage last year, and one of the first things I did was a full service. This included fresh fork oil. The owner had never attended to this and I was present when my tech opened it up. He said the smell was so bad he had to turn on his bench fan lol.
PS: I had the pleasure of not only the company of Dave Moss but also one Mike Canfield, both of them seated at the very same table is I was at the last AFM Banquet this past January 21st.