Suspension help needed

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12/14/2018 11:14 PM

So ive got a 19 kx 450, and need some help on the suspension.
I'm 6feet, 160 pounds without gear. 

Dynamic sag at 105mm, static sag at 50mm. So according to numbers i need a softer spring.
The rear end does not track straight over bumps, it feels nervous when the track gets rough (especially when accelerating) and has a springy feel over g-outs.. But i also managed to bottom the shock a couple times. So do i need to install a softer spring, and increase the damping? Just seems weird.

And the forks are definitely too soft, i bottom them regularly and they travel too much over small bumps. So i think of going to stiffer springs (already tried to increase damping and oil volume) 

Does that make any sense? Softer spring in the rear, but stiffer damping, and stiffer springs in the front? I really dont want to throw off the balance of the bike.
How important is static sag?

Thanks in advance

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12/15/2018 2:45 AM

Where do you have your clickers at? If your off there it will not matter what spring you have. If you are at 50mm race sag you do need a softer spring. How are you measuring sag, standing up or sitting down?

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12/15/2018 5:01 AM

Springyness is a damping issue. To me it sounds like you need springs and valving

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12/15/2018 6:47 AM

Have you adjusted your clickers front and rear to try and fix your feeling? I’d try all of that first.

At 160, depending on your speed, you should be in the ballpark for a 450 spring rate.

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12/15/2018 9:44 AM

I'm the same weight and from stock clickers using stock springs I went 2 stiffer and 1 slower rebound on front. The rear at first would bounce side ways any jump or bump that I hit. I wanna say I went 2 softer on low speed compression as well as 2 slower rebound. But yes we need a spring rate softer in the rear. I'm about to do that as well as add more oil to the front forks for bottoming.

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12/15/2018 2:16 PM

Try 100mm of sag

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Livin' the dream, two wheels at a time!

12/16/2018 12:35 AM

DB97 wrote:

I'm the same weight and from stock clickers using stock springs I went 2 stiffer and 1 slower rebound on front. The rear at ...more

The rear of my bike does exactly that - deflects sideways and up/down over acceleration bumps. When the track is groomed its perfect, but when it gets rough the rear end is hard to predict and does not grip like it should.

My clickers are mostly stock, will try and test a couple different settings (softer low speed comp. and less/slower rebound in the rear).

@sgrimmxdad: race sag at 105, static (free) sag at 50mm. i measure sag sitting down,

@m21racing: will do, thanks

The 2019 kx 450 has a 54nm rear spring, where the 2018 kx450 has a 52nm rear spring, so maybe i will try a stock spring from the previous model and see how that works. How would the lighter spring influence bottoming resistance? Can you have the same bottoming resistance with a lighter spring with "stiffer" valving or by adding a couple clicks of compression damping?

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12/16/2018 9:11 AM
Edited Date/Time: 12/16/2018 9:12 AM

50mm sounds like it`s a little on the soft side. Normaly it`s a around 35-40mm the rear sinks down on its own weight.
i would try to adjust the preload on the sping to get closer to 100mm so its closer to 40mm.




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12/16/2018 12:09 PM

You need your damping adjusted...the spring rate in the rear is fine. According to Pro Circuit with your race sag between 95-105mm your static sag should be 30-60mm. You're right there. Set your race sag to 100mm, as far as the back end getting sideways on the acceleration bumps, try slowing down your rebound damping and your low speed compression damping.

Fork wise if bottoming isn't a bad thing...unless it's clank bottoming and causing you problems with your wrists/forearms. You say you added more oil...go to the max oil volume in the manual and see if that works out better for you. What do you mean the forks move too much on the little stuff? You want them to be compliant on the chop, but not harsh/clank bottoming on the big hits

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Many thanks to everyone helping me out this GNCC season: SRT Offroad, Acerbis, FCR Suspension, O'Neal Racing, Evans Waterless Coolants, Rekluse, Twin Air, Braking Brakes, Carbsport

Profile image credit Ken Hill Photography

12/16/2018 1:09 PM
Edited Date/Time: 12/16/2018 10:22 PM

harescrambled wrote:

You need your damping adjusted...the spring rate in the rear is fine. According to Pro Circuit with your race sag between ...more

Alright, thanks for the info. Will leave the stock rear spring then and try to adjust the clickers a bit.

Well, the forks are very smooth over bumps (as i already said, they seem to travel too much even over small bumps), but have got almost no bottoming resistance. When i overjump a jump just a little bit, they bottom out way sooner than they should (clank bottoming as you call it). I would like to have about half an inch of travel left for when i really case a jump hard.
Would harder springs help with that or can it be adjusted via oil level (i already am almost at max. Oil level) and valving/clickers?

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12/16/2018 10:00 PM

You are over-sprung in the front and rear... Static sag should be between 30-40mm...

At 160lbs I would be around a 46s in the front and 5.2 in the rear...

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12/17/2018 10:38 AM

harescrambled wrote:

You need your damping adjusted...the spring rate in the rear is fine. According to Pro Circuit with your race sag between ...more

mnomis484 wrote:

Alright, thanks for the info. Will leave the stock rear spring then and try to adjust the clickers a bit.

Well, the forks are ...more

Don't listen to the above, 45-60 and no matter what you do with clickers or damping shock will work like shit.
Get you to 35-40 with 105 sag and 4-8mm preload before you even try to fix anything else. Kawi has been soft in front springs for 2019, so don't touch that yet.

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12/19/2018 5:39 PM

aees wrote:

Don't listen to the above, 45-60 and no matter what you do with clickers or damping shock will work like shit.
Get you to ...more

Preload dimensions don't really mean that much, unless you're worried about coil bind. If the OP sets the shock spring preload to where race sag is 100mm, static sag should fall right around 40mm. Leave it at 105 mm sag, and the front end will most likely feel vague, push in the corners and the bike won't turn well, although it'll be stable at high speeds.

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Many thanks to everyone helping me out this GNCC season: SRT Offroad, Acerbis, FCR Suspension, O'Neal Racing, Evans Waterless Coolants, Rekluse, Twin Air, Braking Brakes, Carbsport

Profile image credit Ken Hill Photography

12/20/2018 3:34 AM

mnomis484 wrote:

Alright, thanks for the info. Will leave the stock rear spring then and try to adjust the clickers a bit.

Well, the forks are ...more

aees wrote:

Don't listen to the above, 45-60 and no matter what you do with clickers or damping shock will work like shit.
Get you to ...more

harescrambled wrote:

Preload dimensions don't really mean that much, unless you're worried about coil bind. If the OP sets the shock spring preload ...more

No it won't. 100mm and soft spring and your suspension will be harsch as hell. Stiff or right spring and 100mm you will get poor traction and possibly armpump. No racer or team run as low as 100mm sag today on ktm or husky other then for supercross. Even then they are above 100mm.

There is no benefit today of running less then 105mm sag for MX on this generation of bikes. If you run only rock hard smooth tracks you might get away with it but still with poor traction. And as soon as you try racing a beaten up track you will see all the negatives.

If you experience issues with turning with 105mm/ 35-44mm and 5-9mm preload, something else is wrong in your setup...

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12/20/2018 3:36 AM

mnomis484 wrote:

Alright, thanks for the info. Will leave the stock rear spring then and try to adjust the clickers a bit.

Well, the forks are ...more

aees wrote:

Don't listen to the above, 45-60 and no matter what you do with clickers or damping shock will work like shit.
Get you to ...more

harescrambled wrote:

Preload dimensions don't really mean that much, unless you're worried about coil bind. If the OP sets the shock spring preload ...more

Can also say that with 170 pounds and 45nm you will have around 100mm sag and 40mm free on the newer chassis, but NO PRELOAD. Bike will not behave very good. Just a faulty setup.

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12/20/2018 1:40 PM

So i just bought a slightly used 2017 kx450 rear spring (supposed to be 52nm instead of 54 on the 19), will try that with stock clickers and go from there, see how that works.

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12/21/2018 4:25 PM

aees wrote:

No it won't. 100mm and soft spring and your suspension will be harsch as hell. Stiff or right spring and 100mm you will get ...more

Fine, you know everything, and I who race a 2018 model aluminum frame jap bike on the roughest courses known to man, know precisely zero. OP, good luck with your setup...Merry Christmas all!

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Many thanks to everyone helping me out this GNCC season: SRT Offroad, Acerbis, FCR Suspension, O'Neal Racing, Evans Waterless Coolants, Rekluse, Twin Air, Braking Brakes, Carbsport

Profile image credit Ken Hill Photography