Help with "race sag" and "static sag"

[crfsand]

I just got a new 2015 kx450f. Just need some advice. I weigh 225 and would like to mess with the suspension a little. I hear talk about race sag and static sag. First, what is the difference between the two? Second, How do I set it on my bike for my weight. I don't mean to ask dumb questions but any advice would be much appreciated!

[D9ZZ]

I weigh similar and can tell you, you may as well put a spring on the rear.

Racetech website will get you close.

The stock spring won't cut it for us.

[kawamaha]

race sag is the sag with the rider. should be ~105mm. this is the number that must be adjusted.

static sag is the sag of bike without the rider. the number is just to check if you have the right spring.

should be 30-40mm.

now that you have to add a good amount of preload to reach the proper race sag, the static sag

number decreases. that tells you the spring is too soft.

as d9zz said, go to the racetech site, there's a spring calculator

Edited October 15, 2014 by kawamaha

[mx317]

A friend of mine is around 225 lbs and a 5.8 kg spring works for him.

[crfsand]

Thank you for all the good advice!! How do I measure the "sag"?

[bryce_31]

YouTube is your friend! Jump on there and it shows you how to do it all! But it's from the axle to the number plate dearest point, someone else might explain a lot better but honestly YouTube is great at helping with it as I have just done it myself lol

[kawamaha]

How do I measure the "sag"?

for example:

http://www.werproducts.net/Setting-Rider-Sag.html

[bedge5527]

Go to race tech.com. The best purchase I made for my bike was the rear spring.

[gordybaird801]

Buy the Motion Pro Uni-Sag. $50. Rear shock as well as Forks. Does it all. One person tool. Gordy

[Carl Clonts]

i bought a 2012 kx450f recently. decided to finally set the race sag. at least tried to get in the ball park. 

initial measurements were

593mm

555mm

508mm

sag was 85 and static was 38.

2nd adjustment got it to:

593mm

549mm

498mm

problem is sag is now 95 and static is 50.not sure where to go from here. will give it a run on the trails and see if the difference is noticeable and/or better. it seemed rear low before and didnt seem to turn like it should. hopefully i will like it better now. if not, then its new springs i guess. what does a static # that high do? and will 95 sag be ok for a 52 yr old that just started running the trails again? used to spend some time on the tracks, indoor and outdoor so have some experience but by no means a ripper.

               Thanks for any advice.

[mlatour]

How much do you weigh?   (by the way 593- 549 = 44mm)

95mm of race sag with 44mm of static sag (minimal preload) may suggest the current shock spring is too stiff for you. 

(keeping in mind the forks springs must also match to keep the chassis balanced)

 

Sag numbers are suggested starting points, not set in stone to follow but a general guideline to confirm you are in the ballpark with the spring rates.

The amount of race sag alters the chassis' geometry, the manufacturer's recommendation is where they think it will handle it's best.

Less race sag will make the bike steer quicker with the risk of 'knifing' if too severe and, have less stability at speed, moreso apparent in soft soils.

Too much free sag will make for a 'disconnected' feel of the rear wheel, too little doesn't let the suspension conform to the terrain as well.

 

Even with the correct springs, in most cases when an MX race bike is used for trail riding,

it's rather the stiff interval valving set up for motocross racing that isn't well suited,

not only for plushness but rather for it's inability to comply to small / square edged obstacles,

deflecting off them instead of absorbing so, negatively affecting traction and handling.

No external adjustments (spring rates, preload, clickers) can compensate for that.

 

MX race bikes in general aren't very well suited for trail riding unless in faster/open terrain,

their tall 1st gear, close-ratio gearbox and, tendencies to overheat (4-strokes w/no cooling fan) make them less than ideal.

Can they be trail ridden? Sure, why not if that's what you already have.

Are they the right tool for the job? In most cases no, but that's another topic of discussion.

Edited November 7, 2020 by mlatour

[Piney Woods]

Go to the suspension forum and read the first two. Again.     Again.                                                                                          Again