Dual Spring setups.

[mxbundy]

What I am talking about here is a 2 spring setup on one shock. Like the shocks on the front ends of quads or old vintage bikes.
What I need to know is what is the formula for figuring out what your spring rates should be.
I know that one spring is softre than the other and combined they equal a rate that is the addition of the 2. Then when the softer spring coil bindes the rate increases to the rate of the stiffer spring, there by giving you a rising spring rate.
I need to know what the formula is for this. What is your rate when you combine the 2 springs? How do you determine at what point the rate increases. I know it is a function of the softer spring, and I would assume that you would vary the rate and lenght of this spring to determine at what point in the travel where it will cancel it self out. How do you determine this?
I am not a math major so I go easy on me! :thumb:

Thanks
Mxbundy

 

[DEANSFASTWAY]

Hi MXBUNDY , It might be easier with just a progressive spring . It would sure open up another degree of tunability if you could change part of the spring rate for different tracks What would really be cool is if you could easily change linkage ratios. On quads youve almost got to be an engineer to figure out the spring rates with swingarm A/ARM length and such They also use spring depession limiters to tailor a curve to where the next rate spring comes in.You know On Quads they do some really trick stuff .I am kicking around the idea of starting a project with Mr Wilkeys influence to utilize WP PDS on linkage less Quad ATV rear ends A local swing arm builder as well . Jeremy probaly knowsmore than anyone in the US about WP and Ohlins PDS and he has some really trick stuff at hand to experiment with. Well probably use dual springs with a limiter or a Version of a PDS Spring. PDS systems are totally position sensitive as are their springs( WP anyway) KAW used alot of progressive springs lately but lots of people scrapped them In certain situations I think they are grand. White Bros sells triple rate fork spring kits but I would think that in a forks(esp new style cartrige forks) enclosed situation all those spring ends and spacers and washer probably could cause some rubbing issues but I have never tried them so I shoulnt speculate.Maybe you could try to find something used and cheap to try out and experiment with.Are you thinking for the CRF? Front or Rear? Mr Wilkey is out of headquarters at an event this weekend doing service but maybe someone from the spring industry will come in and shine a light .GOODLUCK

 

[DEANSFASTWAY]

I dont really know the formulas either but Ill try to get to the library . I always wanted to know formulas like Weight overSpring =force on wheels andweght over lenth of arm on an axis needs what weight spring . I guess this is like mechanical engineering and like trigonometry and stuff . I never went to college just the school of hard knocks.Someone browsing has got to know.

 

[mxbundy]

Thanks Dean,

I am actually going to build a shock for my old vintage bike. A 81 YZ-465.
It has a really long shock that goes all the way up under the tank.
It came with a progressive spring on it, but it is hopelessly soft. I want to come up with a 2 spring system on this bike.
No onw makes a spring for this bike, either straight rate or progressive. The spring that I am using is an Eibach that was cross referenced off of a car shock. It works great on the big hits and jump landings, but is way too stiff on the little bumps.

thanks
bundy

 

[DEANSFASTWAY]

Bundy Ive heard that White Bros Makes a spring kit for these old bikes and its not in any catalogs . On the older 465 We would also cut another spring clip groove in the shock body by turning on a lathe. Ive got a stock shock in my sghop right now for 465H as well as a Works Perf aftermarket. The Works shock looks sano but doesnt work very well at all and rides real low $800 . We put the Works shock on the Dyno and brought the peeds up and it just blows right through the stroke. The customer sent it back and still real soft and mushy . I added more comp to the shock but still I feel it is not enough. I want to convert the shock piston ( check ball,spring orifice type) over to a WP Shim piston . Ill do this after the riders second race or so . He ravces AHRMA out here in the East.So I know where youre coming from . Actually , A PDS type shock with a progressive spring would be really good . But I dont think WP builds anything long enough . Maybe Jeremy Wilkey knows more . I asked hi,m about it before but Theres nothing available. White brothers used to do real good mods on those back in the day . Maybe you can still get the spring setup . Ill call them . With this Works shock you still use the stock spring setup Maybe that dual spring setup is what we both could use.

 

[mxbundy]

Good job Dean,

Yes we are after the same thing.
I have a line on an Ohlins shock.
I am having one built from scratch. That is why I needed the info onthe springs.

Thanks
bundy

 

[DEANSFASTWAY]

Called white bros , the current suspension manager says they no longer make the stuff and cant get it . But Ill try some other sources .

 

[KiwiBird]

Bundy, on my 81 465 I had the shock moded for dual springs. I used the small spring from a 78? IT400/425 and then the heaviest Yamaha spring for the 465. Rather than cut new circlip grooves we used a spacer that went to the weld at the end of the body. We used a Pro Tec valving setup in the shock. Worked great.

 

[WhiPit]

FWIW -

I had a '78 YZ-250 (in 1998). I put a WP piston in the shock and added a remote reservoir with adjustable compression damping. It worked great! Had to use the stock spring, too.

 

[mxbundy]

Kiwi,

You had a YZ? Was that here or back home?
The guy building me the shock is in New Zealand.
That is excatly what I have in mind, a helper spring to combat the bottoming. But the guy said the new shock will have a modern valve stack that will control the bottoming mujch better that the old setup. I just want to have a plan in place just in case.

Whipit,

I would love to here fvrom you. How did it work when you were done? How did you come up with a valva stack? How much machining did it take to get the piston on there? I have heard that the shaft doesnt have enough threads at the end to put a modern piston on there a decent valve stack. Where did you source the resevoir with the comp. adjuster on it?

thanks guys,
Bundy

 

[KiwiBird]

LOL, home is here now. It was when I was living in NZ.

Who is doing the shock for you?

 

[mxbundy]

Kiwi,

Robert Taylor is the guys name.
He is an Ohlins distributor.
The shop is called Hawera motorcycles in Hawera Taranaki.
Wow, no thats a mouth full!

Bundy


PS. Whipit, where are you?

 

[KiwiBird]

Bundy - he's a sharp guy, I dealt with him when I lived there, I'm sure he'll do it up good for you.

 

[Swiss]

Originally posted by mxbundy
What I am talking about here is a 2 spring setup on one shock. Like the shocks on the front ends of quads or old vintage bikes.
What I need to know is what is the formula for figuring out what your spring rates should be.
I know that one spring is softer than the other and combined they equal a rate that is the addition of the 2. Then when the softer spring coil binds the rate increases to the rate of the stiffer spring, there by giving you a rising spring rate.
I need to know what the formula is for this. What is your rate when you combine the 2 springs? How do you determine at what point the rate increases. I know it is a function of the softer spring, and I would assume that you would vary the rate and lenght of this spring to determine at what point in the travel where it will cancel it self out. How do you determine this?
I am not a math major so I go easy on me! :thumb:

Thanks
Mxbundy

Mxbundy,
It is pretty easy to do the math, but not so easy to understand why it works like it does. The formula for the actual spring rate is (A x B) / (A + B). So it is the product of the 2 spring rates divided by the sum of the 2 spring rates. Same goes for a 3 spring stack, which I have seen done with older WP shocks. When you figure this out, you will be surprised to find out that the actual spring rate is WAY less than either of the single spring rates! They do NOT add together. Strange but TRUE! With the old WorksPerformance stack system, it used travel limiters to effectively "bottom out" the softer spring in the stack. It normally doesn't happen that the softer spring bottoms out completely and then the stiffer spring is a straight rate. This is why WP developed the bottoming stack, which was a set of rings that sat inside the spring around the shock body. With a spring collar between the 2 springs, it was possible to "tune" the poing of crossover where the dual rate springs traveled enough to bottom the collar out against the ring stack. THEN the second stiffer spring would act as a straignt rate spring. Formulas are available to figure out what rate a straight rate sprint is, but it is pretty difficult to figure the true rate of a tapered spring, because it changes as the spring coil binds the closely wound end and again, like the stacked springs, it is a complex system.
Hope this helps.

Swiss

 

[jmics19067]

Swiss,

correct me if I am wrong,and a questions to answer please,
From what I believe,this is what the problem would be if you had two different full floating springs to support the wieght. For the sake of simple math if you had a 10lb 1" spring against a 20lb1" spring and you placed a ten lb load on the end the 10lb spring would compress 1 inch and the 20 lb a 1/2 inch so the spring would actually compress 1 1/2 inch for the ten lb load,being softer than a straight rate 10lb 1" spring. twenty lbs of wieght would make the 10lb1"spring compress two inches and the 20lb1"spring one inch total three inches travel and so forth until the lighter spring coil binds and then you would rapidly ramp up to the rate of the remaining active coils of the heavier spring . Feeling like a serious spike approximately 3/4 of its travel?
then the fact if you are taking two standard length springs and say you are cutting the active coils in half to fit the shock you are actually doubling each springs rating your 10lb1"spring now becomes a 20 and your 20lb1" spring becomes a 40 so when you actually place ten pounds of weight on it it only moves 3/4 of an inch.The lighter spring only compressing 1/2 inch and the heavier spring compressing 1/4?

So the math maybe not nessacerily hard but would be somewhat tedious to figure out which rates you would need to start with and how much to cut off each spring to get a decent proposed rate? Also why doesn't the lighter spring coil bind? I had heard that before but never quite understood it.

 

[Swiss]

I suppose that you COULD design the lighter spring to coil bind, but it stresses the coil and I have never seen a system that was purposely set-up that way. The WP system was effective adn they even used it with triple rate stacks of springs, with each of the first two using a bottoming ring to pass control from a triple rate to a dual rate and then to a single.

Swiss

 

[WhiPit]

Hey MX!

Sorry, I was gone over the weekend.

On that old YZ, the WP piston fit right on the end of the piston rod - like it was made for it! Now remember, I'm not talking about a WP PDS piston - this was an old-style WP shock - off a KTM with a linkage.

As for the valving stack, I kinda' just took an educated guess. A couple against the piston face and then went down from there. Man, this was about 6 or 7 years ago........I can't really recall "exactly" what I did with the valving, but it worked okay - better than the stock De-Carbon system, that's for sure!

The reservoir was also off an old WP shock. The hose was a pretty easy set up - just drill and tap the KYB shock tube to accept the hose fitting.

Let me know if I can help some more.

 

[shed]

bottoming coils should be no problem - dont the KTM rising rate springs do this anyway? What about using a stack of belleville washers in series with the main spring as a cheap way to get the dual rate? This would allow you to easily vary the spring rate of the stack by adding or removing bellevilles, and they will compress flat. The only problem is that they may not give enough travel. another suggestion is to run the springs in parrallel with one spring inside the other with a gap to the second spring. This gives the same "dual rate" effect as the springs mounted in series, but it may be qucker and easier to adjust the point at which the second spring is engaged. Formula for this is S(total) = S(1)+S(2).

OR you could run a standard single spring, and find a monster bump rubber - after all, you are only looking for bottoming resistance. The easy way to adjust the position at which these are effective is by adding a nylon shim between the bump rubber and the shock top.