Fork oil, need input.(gsx400e)

[Nessism]

Suzuki did a few stupid things on the GS family of bikes. The stator loop up through the hand control for one, and grounding the R/R through the rubber mounted battery box on some models for another. The point being that if you are just blindly following what Suzuki did in all aspects, on a bike that lacks collectors value, then "blindly stupid" wouldn't be far from the truth.

BTW, did you mix your own fork oil from motor oil and ATF? And do you plan to change your brake lines every two years like Suzuki says to do?

 

[tkent02]

The funny part is the time spent arguing was more than enough to do it right. Fork oil is not about top speed.

 

[Runeight]

The funny part is the time spent arguing was more than enough to do it right. Fork oil is not about top speed.

Funny part is you started the argument in post 13. My signature holds true.

 

[Gorminrider]

Look in chapter 7, page 190. It's an addendum to the rest of the book. (Haynes manual)

Oh!-Yes! that will be the "anti-dive" forks model! Do you have that?

I was looking at page 195.
apology/excuse: It's really hard scrolling non-bookmarked pdf's. I'm glad you have the Haynes though-I've never found a Suzuki shop manual beyond my 81' so Haynes is the only resource I know.

 

[Gorminrider]

Good luck with the air. On mine you have to remove the handlebars to add air…

I think they decided to add some air spring so they upped the oil capacity to shorten the chamber and put air caps on, but never actually thought it through. I think the original suspension setup was for a 125 lb Japanese guy delivering noodles in Tokyo in the winter.

I had my '79 set up with about 2" cut off the springs and 2" PVC spacers; 6 oz of 20 wt fork oil. Ready for Mexico.

My '82 has 15 wt 150cc and no air. It's a little low and soft, but I'm older now. When I consider that a Marzocchi mountain bike fork [same basic design] has 35psi per leg and weighs about 200 with me on it, 7 psi on a 600 lb combo won't do much. It's just a trim adjustment. Usually varying degrees of temporary.

yes, I've never had much luck with air forks on my motorcycles, bicycle pump and low-reading air gauge notwithstanding. ESPECIALLY when there are two valves- Impossible to put the same air in each... Honda did a better job, linking the two forks with an airline so you could do both at once...but I would prefer if they had a gauge included so you didn't lose air just checking it with the push-on gauge!! I've heard of just adding a little more oil as a fudge, rather than messing with airpumps. Whichever needs need pretty good forkseals to hold the higher airpressure and I've just about given up on it.

 

[Steve]

(Additional) air pressure is just to adjust the preload to get the "sag" correct. Added air also has the ability to leak out, so you lose that preload. It is much better to install better springs that can be customized for YOUR weight (not the lightweight Japanese test rider) and not rely on additional air. You won't have to worry about checking the "sag" on your suspension for at least another 30 or 35 years, which makes it all worth it.

And for those who install heavier fork oil to "firm it up", I shake my head. The springs are what keep the front end from diving, the oil viscosity only determines how fast it will dive. Installing heavier oil will still let the forks bottom out on heavy braking, it will just take longer to do so.

Back to your regularly-scheduled discussion. :-\\\

.

 

[Guest]

(Additional) air pressure is just to adjust the preload to get the "sag" correct. Added air also has the ability to leak out, so you lose that preload. It is much better to install better springs that can be customized for YOUR weight (not the lightweight Japanese test rider) and not rely on additional air. You won't have to worry about checking the "sag" on your suspension for at least another 30 or 35 years, which makes it all worth it.

And for those who install heavier fork oil to "firm it up", I shake my head. The springs are what keep the front end from diving, the oil viscosity only determines how fast it will dive. Installing heavier oil will still let the forks bottom out on heavy braking, it will just take longer to do so.

Back to your regularly-scheduled discussion. :-\\\

.

Well said.

But finding 'better' springs is a PIA, so shortening the stockers is more practical. If you do some measuring I think you find that you can cut up to 2" off the stockers and that probably ups the spring rate about 10%. Then use a PVC pipe spacer to set the sag and you're in probably the same place for zero $. You DO have to square off the cut end so the spring sits right, plus there is the question of whether to shorten the closer wound end or the wider. You have to leave enough spring length so the spaces between the coils add up to the travel PLUS the preload distance [cap depth plus projection] to avoid coil bind.

It's been two decades since I last did this, but will probably be doing it soon. There's a humpy bridge - clank! - on my usual ride that I'm tired of slowing down for.

 

[Runeight]

Oh!-Yes! that will be the "anti-dive" forks model! Do you have that?

No, both forks are the same however everywhere I read it's more fluid on the left side (brake side) than the right side. At least for my year/model.

 

[Steve]

But finding 'better' springs is a PIA, so shortening the stockers is more practical.

Would you believe that it's actually as painless as clicking A LINK? :-k

The link will take you to Sonic Springs. The owner is Rich Desmond, a member here. If your bike is not listed, contact him through his website or a PM here, I'm sure he can find something for you. :encouragement:

.

 

[tkent02]

Almost as easy as checking the oil level in the forks.

 

[Gorminrider]

No, both forks are the same however everywhere I read it's more fluid on the left side (brake side) than the right side. At least for my year/model.

Ah, well! We need a "Go-To-Guy" for these. Yer it!

Someday, someone with this bike, will ask, "How many links in the chain?" Your mission, if you choose to accept it, is to correct me when I say , "104!"

 

[Guest]

Almost as easy as checking the oil level in the forks.

Depends upon where you live. Customs, cross border shipping, exchange rates.

My way, I'm done in an hour and gone riding. No paperwork.

 

[RichDesmond]

Well said.

But finding 'better' springs is a PIA, so shortening the stockers is more practical. If you do some measuring I think you find that you can cut up to 2" off the stockers and that probably ups the spring rate about 10%. Then use a PVC pipe spacer to set the sag and you're in probably the same place for zero $. You DO have to square off the cut end so the spring sits right, plus there is the question of whether to shorten the closer wound end or the wider. You have to leave enough spring length so the spaces between the coils add up to the travel PLUS the preload distance [cap depth plus projection] to avoid coil bind.

It's been two decades since I last did this, but will probably be doing it soon. There's a humpy bridge - clank! - on my usual ride that I'm tired of slowing down for.

Always cut the closely wound end off, that's the softest part. The other issue is that shorter spring is more highly stressed than it was originally. Given the crappy steel they used in springs back then it pays to check the sag periodically to make sure the springs aren't sacking out and derating.
You'll still end up with a spring that too soft, but it will be better than stock, at least for a while.

 

[RichDesmond]

Would you believe that it's actually as painless as clicking A LINK? :-k

The link will take you to Sonic Springs. The owner is Rich Desmond, a member here. If your bike is not listed, contact him through his website or a PM here, I'm sure he can find something for you. :encouragement:

.

'Preciate the plug!

Unfortunately, we don't have springs to fit the 400/450 bikes, the smallest OD we stock is 24mm and they won't go in those soda straw fork tubes. We can do a custom set, but that gets a little pricier. When it slows down this winter I'll probably run off some 22mm springs, fair number of mid-late 70's bikes they would fit. May have to charge a bit more for them, they are a pain to coil, especially in the higher rates.

 

[Guest]

Always cut the closely wound end off, that's the softest part. The other issue is that shorter spring is more highly stressed than it was originally. Given the crappy steel they used in springs back then it pays to check the sag periodically to make sure the springs aren't sacking out and derating.
You'll still end up with a spring that too soft, but it will be better than stock, at least for a while.

I don't think that the close wound end is softer; it just coil binds earlier and then you get the rate of the shorter remaining part. I guess it comes down to whether you want that progressive rate or not. I have mixed feelings.

 

[Guest]

I don't think that the close wound end is softer; it just coil binds earlier and then you get the rate of the shorter remaining part.

No, Rich has it correct. The more closely spaced coils are the softest rate end of the spring.


Mark

 

[RichDesmond]

I don't think that the close wound end is softer; it just coil binds earlier and then you get the rate of the shorter remaining part. I guess it comes down to whether you want that progressive rate or not. I have mixed feelings.

More coils per unit length makes a spring softer. You are right about how a progressive spring gets stiffer, it's the coil bind of the softer part that does that.

Progressive bad, linear good.

http://sonicsprings.com/catalog/straight_vs_prog_tech_article.php

 

[Gorminrider]

More coils per unit length makes a spring softer

am I learning something? Is that because of the angle of each coil in the "more coils per length" being further from "vertical" than each coil in fewer coils per length ?

ie: a vertical force applied to a horizontal rod being easier to bend than applying the same vertical force to a rod at 45 degrees .... Applying vertical force to a vertical rod is the stiffest of all, being a column ...?

 

[tkent02]

Rocket science... more coils equals a softer spring. Wait, do rockets have springs?

 

[RichDesmond]

am I learning something? Is that because of the angle of each coil in the "more coils per length" being further from "vertical" than each coil in fewer coils per length ?

ie: a vertical force applied to a horizontal rod being easier to bend than applying the same vertical force to a rod at 45 degrees .... Applying vertical force to a vertical rod is the stiffest of all, being a column ...?

Reasonable theory, but wrong. It's not the angle, it's the total length. Think of an unwound spring, i.e. a long thick wire. The longer that piece of wire is, the easier it is to bend.
The four parameters that control spring stiffness are wire diameter, coils/unit length, OD and total length. If you hold wire diameter constant, increasing any of the other three increases the total wire length and makes the spring softer