MX Pro air pressure
I have a set of new Marzocchi MX pro forks on my trek, it seems when I have set them up I need to run lower than the recommended air pressure to get 20-25% sag. The book says 30-40 psi for lightweight riders (i am 64kgs) and I have had to go to 25psi to get anything like that. IS it ok to run them that low to achieve the sag ?
The trouble is when I do run them at 25psi they fell a little too plush for the first half of the travel and then ramp up hard for the last half. I tend to use half of the travel when climbing out of the saddle with my weight forward, but then I can only just get full travel from them on big hits (minus about 5-10mm) .
However if I run them on higher pressure then I get too little sag and I cant get anything like full travel from them, Is my set up flawed, or is it the norm for this fork ? DOnt get my wrong they are a lot better than the garbage forks I used to have but just wondered if my set up is wrong.
First let me start by saying....
that Marzocchi's recommended air pressures usually run a bit high. And keep in mind that they are "recommended" air pressures! , not set in stone, you can run what works for you. Now as far as your "symptoms". Sounds pretty normal to me. You want a fork that is active, yet ramps up for the last 1/3 to 1/2 of the travel to avoide harsh or frequent bottom out. And you should only use full travel on the very biggest hits that you take. You don't want to use full travel all the time. If you do then the fork is REALLY too soft.
As for adjustment's I have to ask you this question. Are you using a low pressure air pump (0 to 100psi range on the gauge) or are you using the more common high pressure pump (0-300psi)? If you are using a high pressure pump, I would suggest getting a low pressure. The reason being is that your MX Pro has a large air chamber that is designed to operate a low pressures (under 100 psi). Very small increases or decreases in pressure in such a system can have a dramatic affect on how the fork feels and performs. As little as 2 to 3 psi can make quite a difference. And fine tunning on a large volume air system is often a matter of making small (too small for an HP pump to be accurate) pressure adjustments. Also, don't get hung up on the 20 to 25% sag "rule". It isn't a rule, it's a starting point like any other adjustment. I've had forks that performed best with as little as 10% sag before, and others that did better with up to 30%. It just depends on the fork! So don't be affraid to try different sag/air pressure settings. Also, just a side note, only make ONE adjustment at a time! Then go ride and see what that did for you. Then make the next and try again.
So the things to remember are. ALL settings are "recommendations" NOT requirements (this does not apply to oil volumes). Unless there is an absolute minimum and/or maximum listed, then you want to stay within that range. Large volume/low pressure air chambers require low pressure pumps in order to set them up accurately. 90% of the time you will not or should not be using full travel. And if you are standing up hammering the pedals in a climb, unless your fork has a lock out, pedaling platform, or is set up quite stiff, you're gonna use about half the travel. An unassited fork (no platform or lock out) is gonna bob when hammering out of the saddle, it can't be helped. If you set it up so it won't then you'll be pretty much riding a ridged fork under any other conditions. Air springs are very progressive, they start out plush but ramp up quickly as they compress. This is normal and one of the great things about air springs. As for the harsh ramp up, this will get smoother as your fork "breaks in". Finally, don't expect the fork to be perfect. You'll find the sweet spot if you work at it. But keep in mind the MX Pro is quite limited as far as adjustability goes compared to many forks. You have air pressure and rebound damping and that's about it (unless you have the ETA model, but that's not really an adjustment).
So, have at it. Fine tunning your fork and finding that "sweet spot" is half the fun.
"I do whatever my Rice Cripsies tell me to!"
Thanks, a helpful reply, it seems you have exactly described all the charecteristics of my forks, and all seems normal, you are right though I am using a 300psi guage and I accept small increments are hard to judge
Also, if you find the fork bottoms out too easily, try running a heavier-weight oil, which will increase compression damping somewhat (you'll probably need to speed up rebound accordingly)