KZ650 progressive springs

What is the right guidance about upgrading fork springs to progressive one?
I have nom. length from original springs 444.5 mm.
Progressive springs should be the same length and no manuf. specify the length only compatibility... how can one be sure.

Has anyone have compatibility data for progressive spring manufac. bellow?

• Wirth
• Hagon
• YSS
• Wilbers

Which make/model works best?

Tnx

 

I wouldn't bother with progressive springs on a 650. They really make little difference. I put progressive in the black bike below, tried it, then added 1/2 inch of pre load to the progressive springs, tried it. Eventually got the best feeling from stock springs and an inch of pre load.
Save your money and use preload instead. 
​​​​

My .02 -
Go with a straight rate spring sized for your weight and the bike’s weight. You’ll need spacers but any good seller will tell you what you need.

For spacers you can probably go with 3/4" pvc pipe or 25mm aluminum tubing.

Straight rate springs from Sonic are in my 750.  They work great, and no need for air like before.

 

Thanks.. interesting perspective...I do want to cut costs..
It is interesting, originals do not even have any wear. I still have ~10mm to go  by the manual ..so.. preload it is..
 

wrote:

Thanks.. interesting perspective...I do want to cut costs..
It is interesting, originals do not even have any wear. I still have ~10mm to go

 by the manual ..so.. preload it is..

 

Adding preload will increase ride height, but not the spring rate.  For that, you can cut some coils from the existing springs and replace the lost length with a PVC spacer.  Cut the end of the spring with tighter wound coils (if there is such a thing on the spring.)  2"-3" of removed coils will make a noticeable difference.

New springs are about $100 bucks a pair. Wipers and seals are about $60 bucks a set for OEM, which is the only way to go. Then the cost of fork oil, $20 or $30 bucks. Total less than $200.
Now you have forks set up for your weight and you won’t have to think about them for another twenty years or more except for changing fluid, which many don’t bother with. If you’re gonna have the messy things apart you may as well do it right. That’s me anyways but I understand there’s them that likes fiddling with them. Not me.
I understand wanting to keep costs down but sometimes you have to spend, and good suspension is worth the money.