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Quote:
Originally Posted by Dougal
I was going to ask the same thing (and I'm sure Sergio has told me in the past too)
Bilsteins stated forces are at silly high shaft speeds (IMO) for general use.
I've re-shimmed the foot valves in my Koni's to reduce the low speed bump harshness, worked a treat (after wrecking the foot valves I had, which were two steps down in bump valving from the stock TLC settings)
http://www.aulro.com/afvb/modified-z...absorbers.htmlQuote:
Originally Posted by Dougal
post #4 ;)
so, sort of apples for apples as they are both 82 series. And as in that thread, I can not tell you any more than those figures. I got them from Toperformance.
note: these are the same 82 series Koni's for Toyota LC 80 series that I run.Quote:
Originally Posted by rick130
Rick, did changing the shims only affect bump? or does it have a side affect of rebound?
Bump only.
I found the other new set of foot valves I have too, but cant recall what spec they are as the bags have deteriorated......:(
Dougal, the rule of thumb for suspension frequency in Hz came from the attached pdf file. The figures I gave for corresponding spring rate per 1000 lbf were my calcs. I will re-check, tomorrow maybe when I have more spare time.Quote:
Originally Posted by Dougal
However at no time was 1.35 Hz given for the front. 1.35 Hz is only for the rear springs when front springs are 1.1 Hz. The suspension frequency at the rear should be somewhat greater than the front.
Edit: sorry, in my rush, searching for the original source of my info, then somehow :angel: I read the wrong bit. Indeed the original 1.35 Hz front with 1.69 Hz at rear was correct. (end edit)
Serg, I'm not sure what you are describing with the pogo stick analogy. If you understand the following, you might be able to describe the issue in another way.Quote:
Originally Posted by uninformed
Suspension frequency figures provide a measurable method to compare ride characteristics of vehicles with widely different weight, for similar use/terrain.
The reciprocal of frequency (1/Hz) gives the period in seconds.
Simplistically, as this applies to suspension, the period is the time (sec) for the suspension to return to the normal ride height when it is disturbed by a bump. For this discussion call that period t1
Depending upon vehicle speed and wheel base, the rear wheels hit the same bump some short time after the front wheels. Call that period t2
Ideally, to make the pitching more comfortable, it is desirable for the rear suspension to return to the normal ride height at the same time as the front wheels.
This means that the period for the rear suspension t3 = (t1 - t2).
The the ideal rear suspension frequency, to 'balance' the pitching is 1/t3 Hz.
Clearly, the suspension frequency at the front needs to be somewhat less than for the rear.
If they are not reasonably 'balanced' then you will have pitching when the front wheels hit the bump and then pitching again when the rear wheels hit the bump.
Suspension frequency is not the only consideration, but it is part of having the 'full picture' and particularly when you have found what is good for your use and what the same ride characteristics from a different vehicle.
John, in your post #13, you say
"For general on and off road, the desirable natural frequency is about 1.35 Hz at the front and 1.688 Hz at the rear. This corresponds to a spring rate of 186.40 lb/in for every 1000 lbf on each front spring and 291.42 lb/in for every 1000 lbf on the rear springs."
That is where Dougal and I are reading 1.35Hz for the front. I based my calcs on the wrong lb/in per 1000 lbf. I re did them with the correct 186.4 lb/in per 1000 lbf and it still gives me 234 lb/in springs.
Pogo stick. Well i'll try again. It feels like bouncing up and down, but I would say not in unison, but slightly seesawed. i.e. front/rear/front/rear/front/rear.
Currently at 210 lb/in front and 250 lb/in rear springs I'm at 167 lb/in per 1000 lbf front and 244 lb/in per 1000 lbf at rear.
Looking at your info, rear springs are about 1.25x the front for frequency, or about 1.53-1.55x the front spring rate per 1000 lbf on the springs. Given my current figures, im quite close and will be al most on the money when the 190 fronts go in. I guess then it comes down to my shocks and their valving?
I must be much closer than LR as their rears where 320 lb/in in my truck. Not sure of the fronts, looks like possibly 154 lb/in, but with a little less weight over them due to my bar and winch.
I haven't said that and I'm sorry if it came out that way. The thread is about spring rates, and my advice for a 4x4 that sees much off road use, on rough tracks or when good articulation is wanted, is to use the longest and softest springs that will do the job.Quote:
Originally Posted by debruiser
With soft springs the rebound valving needs to be lighter, which means the shockie may have to absorb more of the energy on the bump stroke. That also helps with body roll to some extent.
If your shockies are valved to hard, for what they need to do, then changing that will improve your suspension.
Tuning shockies is more difficult than selecting springs. It is made easier if the correct springs are chosen. And very hard to tune shockies to fix issues caused by poor spring choice.
I don't consider myself qualified to tune shockies, or give any more asvise than the general stuff above,but I am working on improving my knowledge.
My own shockies are pretty fancy and reasonably easy to adjust just about every parameter. And I have a smart software package that gives more information about just about every performance aspect, much more than I can understand and properly deal with at this stage.
Serg, thanks for pointing that out, I stick by what I said in post #13, and have gone back and edited the reply I made to Dougal, to correct my bad fubar. Yesterday was chaos, I apologise to you and Dougal, sorry.Quote:
Originally Posted by uninformed
Taking back up the comments out 1.35 Hz producing springs that are too stiff. Do not base the calculations on the weight measured at the wheels, that will definitely produce springs that are too stiff.
To caculate the natural frequency of a spring, like any flexural structure (or member) e.g. a bridge, you need to know the mass supported by the spring (or structure). The axle assembly, wheels and tyres, plus half of the suspension arms, must be excluded as the springs do not support their mass.
If you go back to early in my second post, I showed that it is easy to determine the force and mass supported by the springs (spring force = rate x deflection). If you don't know the specified spring rate it is easy to calculate, the free length and installed length of the spring is relatively easy to measure.
Your further comment about the pogo stick effectis what can be reduced by selecting the right balance between the frequency of front and rear springs.Quote:
feels like bouncing up and down, but I would say not in unison
If it does turn out that the 'rule of thumb' for the target frequency produces too high (or low) a spring rate, that is no reason to ignore the balance between the front to rear frequency.
Edit: it is more usual to choose springs for a desired ride height than frequency. However when you have choices in both the free length and spring rate of springs you can find the best spring that achieve the required ride height with the least compromise for use (off road and on road performance) and comfort.
Thanks for clarifying that John.
Serge, I find springs that are too firm give the feeling of riding on top of the suspension rather than in it. Each bump is felt as a definite event rather than just contributing to vehicle motion.
This is best known in many circles as "riding like a toyota"*. The japanese appear have a completely different suspension tuning process to the europeans and it gives a very different result.
*except for the 100 series, which ride like a boat.
When I inherited my rangie it had 240 lb/in springs in the front and 330 lb/in springs (+2 height also) in the rear.
It was bloody awful in ride, vicious handling at the limit and average traction off-road. I suspect the guy ordering the springs screwed up. It was supposed to be HD in the rear and HD+1 in the front.
Not HD in the front and SHD+2 in the rear.
I was pretty happy with 180lb/in front and back (the rear leveller I think contributes some additional spring rate over bumps) but currently have 240lb/in which I put in for some heavy towing and haven't yet taken back out.
My rear konis (30-1312) are very good when the load matches the springs.
My front konis (30-1426- LC80 fitment) are overdamped but are far better than the koni that were in it prior (84-1124 Rally Spec twin tube).
With my 4BD1T the front and rear axle weights are 1170 and 1130kg with half a tank of fuel. Should be almost equal with a full tank.
Thanks John, as soon as I started reading your latest reply, the light bulb came on and thought, doh, sprung vs unsprung mass.
Lets see If I have this correct for my front end:
Free length: 422mm
static ride height length: 295mm
Rate: 210 lb/in
422-295 = 127
127/25.4 = 5 (to convert to inches as the spring rate is in lb/in, so must be same units)
210 lb/in x 5 in = 1050 lbs.
at the 1.35hz, which is 184.4 lb/in per 1000 lbf, that would be:
184.4 x 1.05 = 193.62 lb/in
If that is correct, my new 190 lb/in springs should be pretty close. Of coarse we are talking about ride and feel more so than handling. I expect with the softer spring to gain a little more body roll and there for, roll steer due to my ride height.
Spring rate check: my coils are 16mm dia wire and according to how "king Springs" count their coils, 8.5 coils. How does that equate to the rate?