Heck, sag is adjusted by adjusting the spring preload with the preload rings, regardless of what spring is on the shock or where the rings are on the shock.

Obviously you'd want the right spring, but it seems some springs aren't the same length as stock ones. No big deal as long as the spring is the right rate and will move enough over the length of travel to not hit coil bind or the rings run out of adjustment either direction.

Example, in the DRz400SM shock swap to the KLX650C, the stock spring is too light. Seems all the replacement springs (Eibach and others) are 10" long where the DRz is 10.25" long. The springs have enough travel to not hit coil bind so the trick is to just put it on and turn the rings to contact and adjust the spring or get a spacer ring to fit between the spring and the adjuster rings to move them further up the threads. Regardless of how it is done, it needs be done. I will check first to see if I need the spacer. I'm thinking not, but if so I will make a spacer.

 

[QUOTE=klx678;524459 sag is adjusted by adjusting the spring preload[/QUOTE]

The confusion on my part is in trying to see how these terms relate. It seems proper sag is determined via measurements to gain a balanced bike geometry and preload is determined via seat-of-the-pants to gain riding style/terrain specific handling. Both are adjusted, at the same time, by changing the nut position - you don't change one without changing the other.

But I did assume any replacement spring would be the same length as the stock spring. I can see how that would make a difference.

 

Sag and preload are related as is ride height.

more preload, will give less sag and more ride height.

There are two paths to less sag, more preload or a stiffer spring. For a given application you'd change spring stiffness, not height. There are no external preload adjusters on the KLX fork. If your preload is wrong, get new springs.

You can make very small adjustments to preload, but first spring strength must be right.

 

"but first spring strength must be right". When I was shopping for a new spring I used the various vendor's online calculators to get "the right spring". The calculators didn't agree. Not even close. I emailed one vendor and they said they spec differently based on preload. So it seems to select the right spring you first need to know "the right pre-load".

 

I'm curious what vendor said they spec differently based on preload? That, to me, is complete horse crap.

If you get to the max preload on the rear shock and you're still getting too much rider (race) sag, you need a stiffer spring. If you're at minimum preload and not getting enough sag, you need a softer spring. If you get the right rider (race) sag by adjusting the preload, but get too much or too little static (bike) sag, then you need a stiffer or softer (respectively) spring.

You get the spring that's correct for your weight and then fine-tune the sag to get it just right. As mentioned previously, there isn't really a 'magical' number for sag, as it will depend on the rider, what kind of riding you do, among other factors, but the figures quoted are often a good starting point. If, say, you want 105mm of rider sag, and you're getting 110mm, and you've got the preload maxed out - technically a new spring would be in order, but if you ride it and it 'feels' right (and you're only bottoming on the very worst stuff you're going to ride), then save the $ and leave it as it is. If, however, you've got the preload maxed (keep in mind that max preload isn't necessarily using all the threads on the shock - many manufacturers list the preload range which is much smaller that what all the preload threads on the shock will give you) and you're bottoming numerous times on your ride and it doesn't 'feel' right (this is a tough one, since most people likely won't know what 'right' is until they're ridden with the suspension properly dialed in), then it's time for a different spring.

 

For me, this guy's guide had the most understandable description of how suspension works and how to adjust it. See what you think.

kb1

 

Yeah, there's some very good info there - too bad his site is no longer 'active' and you can only get to it from the internet archive.

One note I would make about checking rider sag is the 'race tech' method, where you consider stiction - rider gets on the bike and you lift the suspension (if you're checking the rear, you lift the rear of the bike) and then gently let it settle - record this number. Then push down on the bike and gently let it settle up, record this number. The number between the two is the one to use for checking rider sag. This also gives you a chance to see how much 'stiction' you have - if you have a lot of distance (I forget the numbers, but the rear is something like 5mm and the front is more) between the two, then there's a lot of stiction and may indicate that it's time for a suspension rebuild (sticking bushings, seals etc.)