the fork on my new bike has a preload adjuster on each fork leg. I have no idea what they do, apart from turn around and make clicking noises...

anyone know any more??

It makes the initial travel stiffer or lighter. Use it to set the correct sag.

Actually, preload is there to cancel out the weight of the rider. The idea is to compress the spring so that there is a force pushing against the stops such that when you get on the bike your weight and this force cancel each other out (usually set so that there is about 1/2" of sag). It is not a good idea to use the preload to try and stiffen up the ride.

Yep, preload does not increase spring rate. If you have a problem with using too much travel or excessively bottoming, cranking down the preload won't help. It's for setting ride height (sag).

so should it be set so that, from no weight on the bike to me sitting on the bike, the fork travels 1/2"??

Thats sounds real confusing but hopefully someone understands

You have the idea exactly right. I'm not positive on the correct amount of sag though, I believe it differs for different forks etc. You could probably find it with a search. 1/2" seems pretty typical though.

Try going to the fork manufacturer's website, they'll likely have a manual explaining the operation of your fork and the correct setup.

I'm not understanding this thread too much at all.

Pre-load when increased will cancel out the weight of the rider. (which does increase spring pressure) That's the whole point. If there's too much sag, you will bottom out. (unless you like to run tons of sag with tons of compression)

It say's right in my Fox manual:

"Symptom-too much sag and Preload Knob is adjusted fully counter-clockwise"
Solution - "Change to higher rate coil spring" (or put in more air for air forks)

'Thor29' and 'Svr' are confused (no offense )...he/she says:"Actually, preload is there to cancel out the weight of the rider."
-sure, but by increasing spring tension

(Thor says) "The idea is to compress the spring so that there is a force pushing against the stops such that when you get on the bike your weight and this force cancel each other out (usually set so that there is about 1/2" of sag)."
-1/2" of sag for a fork that has 80mm of travel, but what about 4" or 5" or whatever? The general rule of thumb for starters is 15% of sag. I run about 3/4"-1" sag on my 5" travel Fox Vanilla R.

(Thor says)"It is not a good idea to use the preload to try and stiffen up the ride."
-That's exactly what pre-load does. It stiffens up the ride so you don't blow through your travel as much. Granted, you can run more sag with less spring tension, but in order not to bottom out, you will need to crank up the compression damping or change to thicker oil to increase the effect of the compression damping.

The more you compress the spring, the more pressure is required. Especially with air sprung forks and shox. The air chamber is getting smaller and smaller, yet there is the same amount of air in there. It's just getting compressed more causing more pressure to build to cancel out the force. Air is more progressive for this reason than coil springs. Coils are linear, but still require more pressure to compress the spring more. If you barely push on it, it compresses just "so far". If you push harder, then it compresses more.

I'm not getting on ya here, I'm just trying to help clear this mess up.

You're the one that is confused. Spring rate and spring preload (what you're calling "tension") are two different things. On a straight rate, linear wound coil spring, simply compressing it with preload will not increase its rate. A 100lb spring does not become a 150lb spring by preloading it with 50lbs.

The Fox manual is entirely correct and agrees with what I said -- preload will not increase spring rate; if the fork has too much sag and the preload knob is adjusted fully, the spring must be replaced with one of a higher rate.

Okay

Not necessarily - I run about 3" of sag.

You're looking for a percentage of the fork's travel - your fork owner's manual should give you some insight into that and other setup tips.

edit: holy cow, did I get ninja posted or what?

Ya know...my manual says for XC use 15% sag and for Freeride, use 25%.

If I set it up with 25% it gives me less travel, and bottoms out.

Is that a mis-print?