I upgraded my front fork about 6 months ago from the stock RST to a Marzocchi MX Comp. As I've been riding more and more, I'm developing the feel for my suspension and have spent the last few days dialing it in between the rebound and positive air pressure. Anyway - the Marzocchi manual talks about sag (from rider's weight) with the ideal sag being 15-20% for XC riding.

I started with the recommended sag. To get there, I had to let all the air out of the fork. My baseline was 90mm of exposed piston, with my weight, I went down to 78mm, or about 86%. Did some riding around and thought it was too soft so I played with different variations of rebound, etc until I found what I liked. End result was max rebound, turned back 3 full turns and 20 psi. I get about 5mm of sag now, not the 12 I started out with. The fork feels a bit more progressive, more plush, yet I get good rebound. I did get 60mm of compression today on a jump (local handicap ramp at a church across the street).

Anyway - my question on sag is what the true story is - I'm well above the recommended 15-20% in the Marzocchi manual - but I like it more the way I have it now than I used to (40-50 psi, maxed rebound).

It really all depends on your riding style. XC'ers like minimal sag so their fork bobs less and they can transfer more power to the ground. I was going with 25% sag on my 5" dually for bumpin' around. I did a few jumps and kicked it all the way down to around 10% because I was bottoming out.

If you have an "bottom out" adjustment or high and low speed compression dial, you can run more sag and still not bottom out. I only have rebound, so I have to run more preload to keep it from grounding. If you want it super plush, go with 33% sag, little low speed compression, and either alot of high speed compression or more bottom-out pressure.

If you want more efficiency, go with 15% sag, lots of low speed compression or platform...which ever ya got, and then set your high speed compression based on your racecourse.

So, rule of thumb is to start out with around 15-25% and then go from there based on your riding style.

My Marz is set to sag like a 70 year old with DD's. It's all preferance.

Then you need to stay away from flat bars.

thanks, I have only rebound adjustments but can add positive air pressure as well, the Marzocchi manual recommends 40-60 psi based on my weight (6'3", 200lbs). I have yet to fully bottom out this thing, as I mentioned, I could only get 60mm of travel today on some jumps where I got 2 feet of air, and that's about as wild as I'll get so I think I'll ride this for a while until I get the urge to tune it again.

How often should I have the fork serviced? Will playing with the oil weight affect sag (i.e. thinner oil)?

But I love my flat bras.....I mean bars

Depends on how often/hard you ride. Also depends on manufacturer. Marzocchi's can go years without service while my mantiou needed service every 6months.

Thinning out the oil will change the damping characteristics how quickly the fork compresses and rebounds. If you REALLY want to customize than it is worth playing with, but learn to do it yourself. Paying a shop to always do little adjustments gets expensive.