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Air fork Conversion

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I have a 1982 GS550M with air forks. I have always disliked air forks and would like to convert them over to spring only. Has anyone else done this and if so, what spring rate did you choose? I'm just looking for some guidelines on spring rates w/out air and if anyone carries a more stout spring for the GS's. What about maybe using a non-air GS spring? But, I would be guessing at which one would be a good fit...
 
Sci85 said:
I have a 1982 GS550M with air forks. I have always disliked air forks and would like to convert them over to spring only. Has anyone else done this and if so, what spring rate did you choose? I'm just looking for some guidelines on spring rates w/out air and if anyone carries a more stout spring for the GS's. What about maybe using a non-air GS spring? But, I would be guessing at which one would be a good fit...
Click to expand...

Get some progressive springs for your bike (if they make them). Jobs a good'un
 
Cool. Where I'm struggling though is I have no idea what the factory spring rate is so I have no way to judge what I should replace it with. I'll shoot them an email and see what they think. But would be interested in hearing if anyone else has done the swap and what they used.
 
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Sci85 said:
Cool. Where I'm struggling though is I have no idea what the factory spring rate is so I have no way to judge what I should replace it with.
Click to expand...

Doesn't matter with Sonic, they ask you a few questions on your bike and your riding style etc. Then they will match up the springs for ya. Just go to their website and fill it out. What I did.
 
Will do. BTW, how do you like your springs? Did you go stiffer or stock rate?
 
Sci85 said:
Cool. Where I'm struggling though is I have no idea what the factory spring rate is so I have no way to judge what I should replace it with.
Click to expand...
Does it really matter what the stock rate is?
icon_shrug.gif


Look at it this way: you KNOW the stock springs are weaker than they should be, because they were designed to be assisted by air, AND they are 30 years old, so have lost a bit of their "oomph". Does not matter what the rate was, it was wrong anyway. Just get the rate that has been proven to work for your application.

Sonic offers different spring rates, not sure if Progressive has anything other than their "one spring fits all" concept. I have two bikes here with Progressives, they are a DRAMATIC improvement over stock. Over the winter I will be putting Sonics in a third bike, we'll see how it does in the spring. :D

.
 
Of course it matters... look at it this way, The stock spring rate for the 1977 - 80 GS550 was .45 kg/mm, 1982 would be much the same ballpark
after market replacements will be more than double that unless you are a really skinnybitch
Racetech Suspension, offers a variety of springs ..... see if this works, should be close enough to your bike (for spring rates).....http://racetech.com/ProductSearch/2/Suzuki/GS550/1977-80 (there is a link to a spring rate calculator at top of the webpage)
***this spring rate calculator also tells you what the stock spring rate is.
and you may want to consider cartridge emulators as well, ( with labor being so cheap )
Racetech has a decent tech support, phone them before you order anything.
 
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I have done it on a few bikes, I prefer softer springs with more preload, but that just because my back is messed up from riding too many miles on bikes with hard springs and crap shocks.

Going for the BMW like plush ride on all the bikes now.

But anything any of these guys sell you will be a vast improvement over the sagged stock springs which were designed for using air, and designed for a 140 lb Japanese test rider and have been sitting compressed in your forks for 30 years.

Edit - The Emulators help a LOT on these old damper rod forks. Bigger difference than the springs.
 
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I agree. My forks require 20+psi to have any kind of ride quality and I think stock was 17. I put an email into Sonic Springs and I'll probably give RaceTech a call as well. Sure would be nice to know the factory rate though because as Derwood mentioned, you need to know where you are starting to know how much you need to change. I don't think going from .45 if that was the stock setup to .90 would be smart...I'm suprised it's not mentioned in the service manual when so many other things are.

In the interest of education, I will post the results once I get something figured out, ordered and installed.
 
.45 is without air,
preload will make a difference as well, (doesn't change the spring rate, but seems to change how much force it takes to get the spring to start compressing) so you can play with sag settings a little there
if you look through the racetech site they give you the stock spring rate for a lot of different bikes (on the answer page of the spring rate calculator)
I'm using 1.1 kg/mm or so, on a 560 lb street bike i'm about 185lbs all geared up,

pull out a spring (or if you have the forks off) you can measure your spring rate. with a scale and a tape measure and a few sets of hands, some ingenuity
 
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I haven't changd out the springs on my GS's but when I put Sonics in the 06 SV650S I had before it was a HUGE improvement.
 
Went the route your taking on my '81 1100e. At the same time also installed emulators. Very compliant and yet still firm and controlled.

If you are looking for a softish ride I would suggest looking at the lower end of the rate spectrum that spring companies suggest. My experience would suggest that while the rates they propose would not be wrong they would however be at the stiffer end of what you might be expecting.

The damping adjustment on my forks was lost and I don't use the air adjustment with the new springs. I am very satisfied with the results. But personal taste being what it is, when you choose your replacement spring you may want to consider dropping a notch or even two from what they recommend.

Even without the emulators a set of correct rate springs is one of the best bang for buck mods.

You might also consider a fork brace and SS brake lines with good brake pads. Just makes the whole front end feel sooo much better.
 
Another point to remember, though, is that "spring rate" is not all there is to suspension. :-k

"Damping" is another point to consider. Some guys will put in 15w or 20w fork oil to "firm up" the suspension when using stock springs. That really does nothing to hold the bike up, it just slows down reactions. When braking hard, the bike will still dive, but will do it much slower. Only spring rate will keep it from diving as much.

Using a lighter oil, like 10w, along with the proper rate springs will go a long way to adding control while maintaining comfort.

.
 
For the forks, knowing the stock rate really doesn't tell you anything useful. Whether it's a 0.45 or a 0.60, that won't have any affect on the calculation of what you need. This is because there's no linkage or other complication, so all you need to know is the bike weight, rider weight, bike style and intended usage.

The rear of the bike is different, because there's a leverage ratio involved that may not be easy to determine. In that case we work from the bike weight, rider weight, carefully measured sag ratios and the stock spring rate.
 
derwood said:
...preload will make a difference as well, (doesn't change the spring rate, but seems to change how much force it takes to get the spring to start compressing)...
Click to expand...

Good point, and it's the other reason (the first being bottoming) that a too soft spring will actually be less comfortable than one of the proper rate. With a soft spring and a lot of preload, when the forks top out (which happens more often than you might think) it takes a lot of force to overcome all that preload and get the forks moving again, and that's felt through the bars as harshness. Stiffer springs with less preload make that transition much more smoothly and comfortably.
 
Steve said:
Another point to remember, though, is that "spring rate" is not all there is to suspension. :-k

"Damping" is another point to consider. Some guys will put in 15w or 20w fork oil to "firm up" the suspension when using stock springs. That really does nothing to hold the bike up, it just slows down reactions. When braking hard, the bike will still dive, but will do it much slower. Only spring rate will keep it from diving as much.

Using a lighter oil, like 10w, along with the proper rate springs will go a long way to adding control while maintaining comfort.

.
Click to expand...

Agreed.

This combo worked well for me. A set of fork springs that are 'correct' rate for me, emulators and 10 weight oil - as opposed to 15 wt.

Good suspension control at all speeds yet reacts well to smaller road irregularities.
 
I read an article once that was written by the suspension tech on a major race team. He was asked about some specifics about the damping on the race bike, and his answer was "I use the lightest damping possible that will still control the wheel and keep it on the ground." He wanted the wheel to move freely, but not bounce unctontrolled.

When I got my Wing, the previous owner had already installed Progressive springs in the forks, along with the recommended 15w oil. I noticed that at the end of an all-day ride, my wrists were hurting. I analyzed the riding position and found that it was not that much different than my previous bike, but I noticed the pain when I encountered small bumps, like expansion joints on the freeway. Simply switching the fork oil to 10w allowed the wheel to move freely, without the hydraulic lock-up that was jolting my wrists.

.
 
Steve said:
I read an article once that was written by the suspension tech on a major race team. He was asked about some specifics about the damping on the race bike, and his answer was "I use the lightest damping possible that will still control the wheel and keep it on the ground." He wanted the wheel to move freely, but not bounce unctontrolled.

When I got my Wing, the previous owner had already installed Progressive springs in the forks, along with the recommended 15w oil. I noticed that at the end of an all-day ride, my wrists were hurting. I analyzed the riding position and found that it was not that much different than my previous bike, but I noticed the pain when I encountered small bumps, like expansion joints on the freeway. Simply switching the fork oil to 10w allowed the wheel to move freely, without the hydraulic lock-up that was jolting my wrists.

.
Click to expand...

People are often surprised by how compliant a well-sorted race setup is, and by how little the spring and damping rates change from street use.
For example, on a street SV650 I use 0.85 springs. That's for a mix of commuting, touring and sport riding. The race bike uses 0.90s. Granted, the race bike is 45lbs lighter, but even adjusted for that we're still looking at less than a 10% difference. If I was going for a totally comfort-oriented setup I'd put in 0.80s. So the difference in spring rate between "plush touring" and "race bike hard" is just ~15%. The damping range is a little wider, but not much.
 
Well, after consulting with Rich, I think I'm going to go with a set of the .85 springs and 10wt oil. I will post a full report if I get a warm day in to take it out.

Thanks everyone for the feedback. It's been a real help.
 
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