spring rate help

i have a 2002 kx250 and my suspension has been pretty terrible, i have aftermarket factory connection suspension. I have messed around with the clickers, rebound, spanner, etc. Just the other day i took a good look at the tag for the suspension and it said that the spring rate was 5.6kg. I did a little research and found that to be the proper weight for approximately a 260lb rider. . . . i weigh about 160 with gear :banghead:

So i was wondering what spring rate i would need, i was doing some conversions on this site: http://mx-tech.com/?id=home and found that according to them the correct rate for me would be around a 4.8 (i would rather set the suspension a little stiff since i am just 16 and still growing). what do you guys think about this rate? What should i do for the front forks?

well, according to racetech.com you need for MX...

Recommended Fork Spring Rate: 0.433 kg/mm (use closest available)
Stock Fork Spring Rate: .430 kg/mm (stock)

Recommended Rear Shock Spring Rate: 5.20 kg/mm (use closest available)
Stock Shock Spring Rate: 5.2 kg/mm (stock)

hope this helps :thumb:

to need a 4.8 you would need to weigh 120 or less
alright, thanks, i was actually just on there site. Do you think i should just get the stock weight springs front and rear since they are real close to the recommended spring rates? also, do i need any special tools or anything to replace the fork springs?

Thanks a ton
uhhh... i'm not sure on the tool thing, you would have to get a clymer manual, most of the time they have them at your local library. In there they will tell you how to service your forks with out any special tools
When you consider your weight be sure to account for the 20 lbs. of gear your wearing!

I would stick with the 5.6 as it's not much different than a 5.2 and a little stiffer is better.

Try to find out what is currently in the front forks and if it is stock I would go up a little.

Dialing in your suspension is one of the toughest things to do and can take a long to to get perfect after many rides and different conditions. It took me a year to dial mine in perfect as my riding conditions kept changing and I was pushing harder. One of the most important factors to a properly set suspension is to set the SAG. After and only after doing this will you be able to dial the suspension to a well working machine. Good Luck!

P.S. You will also be amazed at how much better your suspension will respond with balanced tires. I know it sounds funny but makes a big difference.
i weigh probably 150 without any gear. thats a good point and i did work on mine a bit this year, mostly just adjusting the spanner, rebound, compression and what not. I did try to set my sag on several occasions however i was not able to get the sag to the right level which leads me to believe that the spring rate is incorrect for me ( i could almost set the static sag right but could not set the rider sag even close to what it should be at, i was stuck around like 60 rather than 105) I'll have to make sure my tires are set evenly, im usually not to perticular with my psi, maybe i should look into that. I usually fill them high then ride and ride them till there low :thumb:
I was not speaking so much about air pressure as I was the balancing of the rim and tire. You know put your tire on a couple of jackstands with the axle resting on each jackstand. Then spin the tire and you will notice where is stops. Then you need to add a litte weight to the opposite side until the tire does not want to stop spinning at any particular spot.
The thing with those spring rate charts is that the information varies from one source to the next. Your weight is about the average that the manufacturers set bikes up for. I think that the stock spring rate would be good for you.
If you can't set the sag to the proper amount then the spring rate is wrong . You're right about that. Another thing to keep in mind is that there is a minimum and maximum length for an installed spring. So, even if you can get the sag set right, if the spring compressed too much or not enough the suspension will not be able to perform to it's full potential.
This site has good info on setting sag and dialing in the clickers:http://www1.enduroeng.com/storage/pdfs/Suspension_Guide-Dec23-LOWRES.pdf
If you call them up and tell them all your particulars they can recommend the right springs for you.
one thing that that hasn't been mentioned is the mechanics of the shock system. My suspension was super stiff and hell to ride on until I messed up the clicker and had to have the shock rebuilt. I guy that rebuilt my shock said the bladder inside the shock was busted and caused the shock to not function properly. I also found my linkage bearings to be rusted up. I replaced all the linkage and shock bearings with the rebuilt shock and OMG!!! it was a new bike. I had to re-learn how ride it was so different.


Staff member
Like Rolls said, if you can't get the sag right then you need a different spring rate.

And like Jackson said, if you haven't greased the linkage recently (if ever, as it's usually forgotten) make sure to check it, it's not as hard as it sounds. :thumb:

Another thing is, when was the last time you had the oil changed? Suspension oil wears out just like motor oil and needs to be replaced.

There's some pretty cool PDF's in here that will help you get your suspension setup.
after i had messed around with my clickers and spanner a good bit, i went to pick my bike up to place it back down and have it sit at the top of its stroke so i could measure the static sag, and i noticed the swing arm would continue moving down after the suspension was done moving, so i took a good look at the linkage. Turns out the bushing where the linkage attaches to the shock wasn't even there. I took the linkage apart, the hole where the bushing was supposed to be was almost all the way broken through. . . probably about 3 or so more rides and the linkage would have broken right through and sent me for a wild ride. I bought a new bearing and bushing kit and was going to get a new arm thats inbetween the dog bones (i need one or it will break through really soon) so i called the dealer and they wanted 173 dollars for the piece :shocked:. I was lucky enough to find one on ebay for 49 dollars plus 12 dollar shipping that needs to rebuilt off of a 99 kx125. I bought that now just waiting for it to ship (should get here around wensday or thursday), ill let ya know how that helps the suspenison, should help a ton!

Ill take some pictures or make a video some time soon since i did a pretty crappy job exlaining it :P