KDX sag settings what should they be?

[155810958]

With all the discussion about fork and shock springs, I couldn't find what the static and race sag should be. From what I understand, sag with the rider on the bike should be about one third of total travel, 3-4 inches, front and rear. This is measured as the difference between the the suspension off the ground and the rider on the bike with gear.

Using this method, (I am about 165#) I get 2" in front and 5" in the rear.

According to everything I read, the front springs are too weak and the rear shock spring is if anything too stiff. My measurements would indicate just the opposite!

I think I should reduce the preload in the rear (static sag is about 2") and if anything use softer springs in the front, or reduce the preload ( static sag in front is about 1").

Any thoughts?


Bruce W

 

[adam728]

Sag should be 4" in the rear. Raise your preload and get it there. I don't know why you would want to reduce preload when you are already using half your travel just sitting on the bike.

The front is usually less by design. I believe mine was around 2". What is actually important up front is preload. The fork springs should be set so that there is 10-15mm of preload on the spring when the fork is assembled. Then if your sag is too much or too little you know you need stiffer or softer fork springs. I don't remember what the ideal number was. I would definitly suggest stiffer fork springs if you are 165 pounds. My bike handled 10 times better with stiffer springs, really helped keep the front end from washing out in corners.

These are just generalizations, you could fine tune to your hearts content and break these rules and have something that works great for your riding.

 

[155810958]

sag settings

Thanks for the reply. Searching this forum it was hard to find info on both front and rear in one place!

Seems you are right -

Front: 25 mm free sag with 10 mm preload, 2" or so of race sag as a start.

Rear: 2" (50mm) free sag, 4" or so of race sag, change preload to suit.

So I should increase the preload on the rear, leave the front as is?

Bruce

 

[oldturtle]

I think you are confused about static sag in rear. As Adam said just correctly set the rear race sag. Anything over 4 inches and you will loose cornering quickness. Anything under 3-7/8 inches and you will loose straight line stability. After getting race sag correct then check static sag. The normally accepted static sag is anywhere in a rough range of about 1/2 inch to 1-1/2 inches. Anything less than 1/2 inch means that you had to crank up preload too much to get proper race sag and that the spring is too soft. Anything more than 1-1/2 inches means you did not need enough preload to get correct race sag and that spring is too stiff. The rear static sag numbers only give a rough indication of correct spring rates where-as the race sag numbers must be met for a proper handling set-up. Your idea of a 2 inch rear static sag could still be OK but many suspension tuners might suggest going a little softer on the rear spring for your weight. For a play bike lots of different spring rate and static sag numbers will work just fine but for everyone you do need to get the race sag in the ballpark.

 

[155810958]

front sag settings

OK, I understand the rear sag setup.

The front I'm still having trouble with.

My front race sag is about 2". Free sag is about 1". This is with stock springs. I think this is about right, so I wouldn't want to install stiffer springs as is usually recommended?

I get the feeling lots of folks on this forum just put in the stiffer springs without really understanding why.

Thanks

 

[adam728]

OK, I understand the rear sag setup.

The front I'm still having trouble with.

My front race sag is about 2". Free sag is about 1". This is with stock springs. I think this is about right, so I wouldn't want to install stiffer springs as is usually recommended?

I get the feeling lots of folks on this forum just put in the stiffer springs without really understanding why.

Thanks

No, they put in stiffer front springs because they understand that the stock ones are only good if you weight 120 pounds and ride slower than a kid on a powerwheel. The stock fork springs are far too soft. I go about 175-180, and upgrading to .40 kg/mm springs was one of my best mods. It made the bike handle 100 times better and allows me to actually hit bumps in a gear higher than 1st without blowing my wrists apart upon impact. The stock suspesnion is very, very unbalanced. It's extremly difficult to get the bike to handle to it's potential until the fork is stiffened up. I push the front end in wider corners and knife it under badly in really tight corners, stiffer springs made it much more controlable. Now I only have my poor riding skills to blame. :laugh:

 

[matt-itude]

try the stiffer springs and removing the compression stack shims (2 on newer bikes with 10 shims and 1 on slightly older bikes with 5) Everyone that has done this including me says HUGE difference.

 

[tptp]

Hi everyone.
I use: race sag (driver on bike) static sag (no driver on bike) and free sag (bike on stand with weels in the air)
Race sag = Rear 100mm (4"), front 75mm (3")
Static sag = Rear 30mm (1 1/4"), front 25mm ( 1")
This figures compared with free sag.

The front fork has to be meassured twice to get the sag.
1) Compress the suspension with the driver on neutral racing position - don´t help the bike to rebound - get the figures.
2) Compress the suspension with the driver on neutral racing position - help the bike to rebound - get the figures.
3) The averidge of this two figures are the front sag.

My problem is to know how much of the driver shall be on the front or rear? This do have a kind of impact on the messurment. Someones may use the rear more and others keeps theire helmet over the numberplate..? Shall it be 50/50 or 70/30 or??

Well, I put in .42 spring in the fork (I´m 80kg 175ibs?) and took away some of the spacers (on top of the springs) to get 15 mm preload, also took 2 shims out. Much better than stock. I am playing on different MX tracks (slower than you guys in the trails/woods) and still the fork seams to be a little soft.

Have some more work to do with oil and comp klicker...but now it does not dive forward. I use to bring the video camera, it´s helpful when analyzing the suspension.

Thank´s and Merry X-mas from Sweden!

 

[kmccune]

10wt oil helped me a lot in the front, if you remember from an earlier thread I run more then stock preload, I can't remember what is is right now I have not had my forks apart since last winter. and the .40 kg springs. That is why I run the forks over the top of the triple clamps to aid in turning due to less front race sag. I weigh 155lbs and this seems to work for me on mild MX jumps. It is a little harsh on trails though. I think I'll get it revalved this winter.

 

[155810958]

tptp - very nice explanation, thanks. Interesting, that you are 175#, and front free sag is 1", race sag 3" with .40 springs.

Mine: Front free sag 11/8", race sag 2" with stock springs! (.35 I think). I weigh about 165# with gear. Based on this I don't think I should use stiffer front springs in spite of what everyone says.

The rear I can "bring in" by increasing preload - both free sag and race sag are too high. Conventional wisdom from the posts is that the stock rear is too stiff, but that doesn't seem to be the case for me.

Still, going over a set of whoops you have to pull up on the bars hard and gas it or the back seems to climb, or the front drops (front wheel landings) which makes me think the rear is too stiff and/or the front too soft, like everyone says.

Maybe I just need to "suck it and see", and make changes. but springs aren't cheap, and I hate to change parts without understanding why.

 

[dmcc]

I can relate to wanting to "understand why", but part of understanding is experience, and it sounds like you're getting it with your description of your bikes attitude in the whoops. The front diving and the back climbing certainly do point to the need for stiffer front springs, regardless of what the common guidelines are.
I'm no suspension expert, but I know how like my KDX to ride. I've owned two and ridden at least 5 others, and except for my current bike, I rode all of them with stock springs and heavier front springs (BTW, I weigh about 185 w/ gear). On every one, the heavier springs made the bikes much easier and SAFER to ride fast. My current bike (used) was set up for a 250lb rider, and even though it is too stiff, it is far better than being too soft (stock).
My $.02 - Ride the bike and enjoy it, ride others with mods if you can get your hands on them, then if you want springs, buy them when it's convenient. And for what it's worth, taking out two of the shims works great! (Read the threads on that mod to learn more)

 

[tptp]

Think of this. If you put more weight on the front than on the rear while measuring the race sag, then you are out of the ballpark. I put maybe to much on the front compared with what you do?
I use .42 springs from K-tech. They are longer than stock, so I had to make the spacer shorter to get my preload at 15mm (or was it 10mm?). Now we have a lot of uncertain fact that affect the suspension a lot...
I learned, first get race sag right, then static sag (free "sag" = 0, or no sag, it is when the suspension is fully expanded), static sag shows if you need other springs.
After that you will set up:
Rear rebound to prevent kicking and packing.
Rear compresion to prevent bottoming more than once at "worst section" at the track.
Front rebound slower if cornering is hard, or faster if cornering is to easy.
Front compression harder until it will be unstable to make smaller changes of direction at high speed, and more oil to prevent bottoming in the worst (nicest?) jumps.
Then play with fork hight in tripple clamps to fine tune steering angel and wheelbase to fine tune stability.
And this is just a part of it...but it is what I learned to be in the teoretical ballpark.

I do not know if I am quite right and please comment this - I´m in this to learn more :-)