Fork spring choices

Got a 1983 GPZ750 stripped down in my living room currently, have most everything sorted to be put back together hopefully by October, critical piece I'm missing though is a new set of fork springs. So far all I've found for new options is a company out of Germany. I'd prefer to get a stiffer straight rate spring as I'm modernizing by eliminating the air system but it's looking like I might not have many options

Curious about what other GPZ owners here did with theirs

Check the fsm for the overall uncompressed length and measure yours. Chances are they are fine. 70s forks were always fairly soft. Easily remedied by adding preliad above the spring. Half an inch is normally sufficient.

I got Sonic Springs for my 750.  They offer a few different rates, based on your weight and riding type.  They come with a hunk of PVC pipe for making spacers, so the basic length of the springs is unimportant.  And with many bikes of the KZ era, the springs were soft, and air caps were used at the top as a spring supplement.  Using air increases fork stiction, though, and the effect changes with temperature.  Since switching to Sonic, I don't use any air at all.

 

I have no doubt the current springs are likely fine as the bike only covered 14k before being garaged and neglected for seemingly 40 years (original model rear tire is still on it), I am eliminating the air though and would like to put in stronger springs while I have them open anyways

I looked at sonic but they only offer KZ forks and not GPZ, which to my understanding are different diameters

Where in the world are you ?

Wookie58 wrote:

Where in the world are you ?

Florida

notgoodwithnames wrote:

I have no doubt the current springs are likely fine as the bike only covered 14k before being garaged and neglected for seemingly 40 years (original model rear tire is still on it), I am eliminating the air though and would like to put in stronger springs while I have them open anyways

I looked at sonic but they only offer KZ forks and not GPZ, which to my understanding are different diameters

You could always try measuring the OD and length, then message or call Sonic.  Racetech is another possibility.

oldbikebarn.com/products/gpz750-progress...mnLsADh5rCMV0fIvBhMU

Or

www.denniskirk.com/progressive-suspensio...-kawasaki-zx750a-gpz

chopper1963 wrote:

oldbikebarn.com/products/gpz750-progress...mnLsADh5rCMV0fIvBhMU

Or

www.denniskirk.com/progressive-suspensio...-kawasaki-zx750a-gpz

Both of these are progressives

Bumping this in case there's something else out there

So what do you not like about Progressive, Race Tech and Sonic?

Check with Wilbers, Maxon, etc. I checked Hyper-Pro and their springs are progressively wound. 

To be honest, unless you’re riding 10/10ths,  you’ll probably never realize the progression of the spring rate.

Later, Doug