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Couple questions.

1)If the frequency in the front is say 1 then I would want the rear to be somewhere around 1.1 to 1.2?

2)Is this front to rear ratio more important for a shorter wheelbase rig like a samurai, Jeep, or baja bug?

1) Yes, at least for speed work

2) Actually, no. The faster you're going and/or the shorter the wheelbase the less important the difference front to rear. It has to do with the time between the front and rear going over the same bump. The longer the time between front wheels and rear wheels hitting the same bump (which you can calculate as (0.0568 * wheelbase in inches) / speed in mph ) the more by which you want the rear suspension quicker/stiffer/higher frequency than the front so it reacts faster and catches up and therefore the front and rear tend to act together instead causing pitching up and down.

I'm going to add a bit more to the article on this and will post it up here too. Should be done today.
 

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Couple questions.

1)If the frequency in the front is say 1 then I would want the rear to be somewhere around 1.1 to 1.2?
Sure, as a BALLPARK, and as a place to start your tuning. If you put it there, leave it there forever, and assume that's where it MUST be then you've missed the boat. In other words, it is a very good place to *start*. Just because I say it's a good rule of thumb, that doesn't mean that's where it has to be or should stay. I can say it's a scenario most likely to get you going in the right direction!
 

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1) Yes, at least for speed work

2) Actually, no. The faster you're going and/or the shorter the wheelbase the less important the difference front to rear. It has to do with the time between the front and rear going over the same bump. The longer the time between front wheels and rear wheels hitting the same bump (which you can calculate as (0.0568 * wheelbase in inches) / speed in mph ) the more by which you want the rear suspension quicker/stiffer/higher frequency than the front so it reacts faster and catches up and therefore the front and rear tend to act together instead causing pitching up and down.

I'm going to add a bit more to the article on this and will post it up here too. Should be done today.
this makes sense, so if the rear is too soft, it will cause the pogo effect? my problem seems to be to get it to go fast in the bumps, with just a standard coil spring and shock set up, is it is rough on the street. if it is comfortable on the street, it is too soft in the bumps, so i try to find a happy medium. i know you can make the shocks progressive to help this, but i am not that skilled on shock valving... yet :) i also still am trying to find out of suspension frequencey can offset weight balance of the rig? how important is 50/50, or even 40/60 in the fast stuff?
 

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OK, I wrote a bunch of stuff on "anti-pitch".

Benny will kick my ass if i don't once again point out that even though I give equations and there's even a new "calculator" built into the BV spreadhseet - this is all just a SWAG starting point.

Anyway, FWIW, it is here (ended up too long to cut and paste in this thread)

http://www.pirate4x4.com/tech/billavista/coilovers/Part_1/#AntiPitch

Oh, I will just add, though, from the article, because I think it bears repeating:

Of interest, and in out favour though, is the fact that we don't need to alter the suspension in any way to test and evaluate different frequencies - we can do so simply by adding or removing weight. Recall that the equation for frequency is:

Fn = sqrt ((386.088 * WR ) / CSW ) / 2pi

and therefore depends only on the wheel rate and corner sprung weight. If we leave the wheel rate alone, by changing the corner sprung weight we can alter the frequency and test that way.
 

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Discussion Starter #25
BillaVista, great addition to the article.

I've got another question rattling around, but only if it doesn't take time away from you finishing the section on valving.:D

How does the frequency of just the main springs on each end come into play?

More specifically, could a person tune the dual rate stop to artificially increase the effective frequency in the rear by having the rear suspension spend more time(as compared to the front) on a given size bump(and speed) in the main spring rate?

I'm thinking of starting off with a 20% difference(good for medium to high speed), and trying to tune the placement of the dual rate stop in the rear if I get too much pitching at lower speeds(<40mph). Plausible?
 

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If you build a suspension for a certain frequency but your suspension hight is way off would you be able to get it where you want it by changing spring length or adding a third rate/helper coil?

Thanks for the help. I've been kicking coil overs around in my head for a while but only had vague descriptions and hearsay to base my opinions on. I suspected that there was more going on than spring rate and droop and before I spend the money I want to understand what I can do to get the most out of them.
 

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Awesome article and discussions (subscribed and have been following).

Its cool to finally be able to explain and *quantify* this "thing" that we've always kind of known- that lighter rigs need matching lighter spring rates to ride/perform the similar to a heavier rig (frequency). With this knowledge we can make measurements and comparisons that are actually useful and not just guesses.

I also appreciate the effort to try to standardize some of the terms. It definitely helps reduce confusion and improve communication! :cool2:
 

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If you build a suspension for a certain frequency but your suspension hight is way off would you be able to get it where you want it by changing spring length or adding a third rate/helper coil?


Hi. I want to select springs for my ST-3.


I am familiar with the math and parameters and have some experience in shock and vibration isolation and I read BillaVista's article as welll.
Something is not sitting for me with satisfying both Frequency and %Droop.
A known value of Fn dictates us a single value of static spring deflection as follows:
1) Fn = (1/2PI)*sqrt(k/m)
2) k*D = m*G (Spring force equals to mass * gravity)
- from eq. 2 we get
3) k = m*G/D
- Putting down eq. 3 i eq. 1 gives:
4) Fn = (1/2PI)*sqrt(G/D)
- from eq. 4 we finaly getting

5) D = G / (2*PI*Fn)^2

- For example, a 1 Hz freq. suspension will always have a static deflection of about 4" regardless of the wheel travel. If so, the amount of %Droop can be only reduced by cahnging pre-load (higer ride height).
- If i have 20" wheel travel I will have 4/20 * 100 = 20% droop.
- If i have 40" wheel travel I will have 4/40 * 100 = 10% droop for same frequency.

I can't solve this - which parameter is the govern one?... any help?
Thanks
 
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