Fork oil, need input.(gsx400e)

[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!"

[John Park]

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?

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.

.

'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.

[John Park]

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.

[mmattockx]

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

[John Park]

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 ...?

More coils per unit length is a longer spring - longer piece of rod = softer. The structure we're considering begins so far out of column that I don't think it's worth that consideration. It's really a coiled up torsion bar. That's why I don't consider the close wound end to be 'softer'; it's going to deflect at the same rate per wind because it doesn't know how closely it's wound until it binds.

I'm in agreement with Rich; cut the close coils. And it's 'rock it science'.

[Nessism]

That's why I don't consider the close wound end to be 'softer'; it's going to deflect at the same rate per wind because it doesn't know how closely it's wound until it binds.

The closer wound coils WILL coil bind, that's the whole idea behind winding them tighter. As these coils wire bind the spring rate will increase.

[mmattockx]

Progressive bad, linear good.

+1.

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 ?

Nope. A coil spring is really just a torsion bar spring packaged more conveniently for our uses. The spring rate of a torsion bar is determined by its length (and diameter and material, but we are assuming those stay the same for our discussion), the longer the bar the softer its rate because the helix angle of the twist is less on the longer bar for any given amount of twist on the end. Since a coil spring is just a torsion bar wrapped up it follows the same rules in regards to spring rate. More coils per unit length means a longer torsion bar per unit length and that means a softer spring rate.

That's why I don't consider the close wound end to be 'softer';

You may not consider it to be softer but the math is very clear that it IS softer.


Mark

[RichDesmond]

...That's why I don't consider the close wound end to be 'softer'; it's going to deflect at the same rate per wind because it doesn't know how closely it's wound until it binds...

You're redefining spring rate here. Rate is defined as the force required to deflect the spring a given amount. The key here is that it's the whole spring. You're looking at an arbitrarily defined section of the spring. Within that context you are correct, the deflection per wind is the same. But there are more winds per unit length, and so the total deflection is greater for a given force. That's the definition of "softer".

[Gorminrider]

by Jove, I think I get it!

...More coils per unit length means a longer torsion bar per unit length and that means a softer spring rate.

"...the deflection per wind is the same. But there are more winds per unit length"

Thanks!