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GS 1000 fork upgrade with sonic springs

  • Thread starter Thread starter gl1ltd
  • Start date Start date
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gl1ltd

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Does anyone know how long the spacer should be for preloading the forks on a '78 gs. I got a set of 1.0nm for about 185 lbs. of riding weight but not sure about the preload. The instructions are vague at best. The springs are Sonics and have worked very well in other builds. Thanks in advance.
 
These forks have the shrader valves for air adjust and no preload caps as is preferred. Thanks
 
gl1ltd said:
These forks have the shrader valves for air adjust and no preload caps as is preferred. Thanks
Click to expand...

Sometimes you can find a bike where the preload caps can be swapped out and used on your bike. Regardless the sag measurements are the same, it is just easier to determine the spacer length with the fine adjust on the fork. You can always rely on air, but that is not really recommended as they leak and without crossover are never the same.
 
Well, the recommended average sag is 35mm.
Measure yours, calculate the difference and cut some PVC pipe to make it up.
Please look up how to measure sag on your own.
 
gl1ltd said:
Does anyone know how long the spacer should be for preloading the forks on a '78 gs. I got a set of 1.0nm for about 185 lbs. of riding weight but not sure about the preload. The instructions are vague at best. The springs are Sonics and have worked very well in other builds. Thanks in advance.
Click to expand...

Have you gone through the Note A section of the instructions while looking at the parts with the forks off? Sometimes they make more sense that way than reading them away from the bike. :)
Don't use someones else's spacer length, it may not be right for your bike.
 
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Well, there ya go, straight from the source.

If you still have your stock spring and spacer, use that length as a first attempt, but be prepared to open up the forks and make a second spacer that is the correct length after measuring the sag with the first setup.

.
 
Steve said:
...If you still have your stock spring and spacer, use that length as a first attempt...
Click to expand...

That will almost always be too long, because the stock springs generally have a lot of preload to (sort of) make up for the fact that they are so soft. Excess preload is very bad. :)
 
Well, it worked quite well on my 850G'K'. :-k

I don't have an exact measurement for the sag, but it does drop just a bit, and the ride is SUPERB. :encouragement:

.
 
On my ED with 88 GSXR 1100 forks with my weight of about 210, the stack height was just enough that I had to really struggle to get the screw in top cap on in the lowest preload setting. The were probably progressive springs.

It is easy enough to trim the PCV till this occurs. Unless you have unusual upper body strength for your weight it should sort of compensate.
 
posplayr said:
On my ED with 88 GSXR 1100 forks with my weight of about 210, the stack height was just enough that I had to really struggle to get the screw in top cap on in the lowest preload setting...
Click to expand...

That's a sure sign that you have more preload than you should. Given that that there's 10-15mm of thread on the fork cap you should only have to compress the spring 5-10mm to get the threads started.

Steve, I'm sure it's a lot better than stock, but you might try spacers 1/2" shorter and see if you can make it even better. :)
 
r;e said:
That's a sure sign that you have more preload than you should. Given that that there's 10-15mm of thread on the fork cap you should only have to compress the spring 5-10mm to get the threads started.

:)
Click to expand...
Well if that is the case it is probably because the springs are too soft. As mentioned I'm not what the springs really are except they are progressive wound and not stock. I also had to cut them to fit. maybe time for some new springs?


I'm pretty sure the preload was set to avoid bottoming out when I went on a rough twisty road (Camino Cielo above SB). However as I recall from zip tie measurements it was heavy braking that caused most of the fork stroke.
 
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If you have springs with the proper rate (and it sounds like the OP does) then this is quite straightforward: a good starting point is to use whatever spacer length will end up with about 3/4" (19mm) of preload with the fork cap installed. Test ride, measure sag, and fine-tune spacer length from there.

What length is that? Without your forks and the new springs in front of me, I have no idea. If you can scare up a pencil and a ruler, you can figure this out for yourself in about five seconds. Ain't hard at all.

If all you can get are springs that are too weak (I used Progressive springs for years before discovering Sonic straight-rate springs) use whatever preload you have to to get sag in the right ballpark. It's not ideal, but it's still miles better than the weak-suck stock springs.

The rule of thumb is that you generally want to target sag to be 1/4 to 1/3 of total travel. So if your forks have 100mm of travel, you want sag to be 25-33mm, depending on your tastes and preferred velocities.
 
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