dblissett
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| posted on 20/1/04 at 08:40 PM |
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spring rates
i am building a mcsorley 442 with a 2ltr pinto what spring rates should i start at for the front i know it will be wrong but i need to start some
where
i have 180lbs for the back end
the dampers are spax if that helps
thanks dave
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chrisg
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| posted on 20/1/04 at 10:31 PM |
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My 2ltr pinto car uses 300lb front springs, seems to be ok, MK use 350lb on the Indy.
Cheers
Chris
Note to all: I really don't know when to leave well alone. I tried to get clever with the mods, then when they gave me a lifeline to see the
error of my ways, I tried to incite more trouble via u2u. So now I'm banned, never to return again. They should have done it years ago!
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stephen_gusterson
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| posted on 20/1/04 at 11:23 PM |
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I have 350lbs on my v6 engined car.
beware - the angle of the shockers matters.
if the front shocks are vertical (never on a locost except the rears) then you get full rating.
If they lay at 45 degrees angle, the rating halves due to angular leverage.
this is from memory, so it might not be as linear as that, but you get the point
atb
steve
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craig1410
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| posted on 21/1/04 at 12:55 AM |
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Steve,
Not trying to be clever (honest!) but I think it is actually Sin(45deg) which comes to about 70.7% of the spring rate acting vertically when the
damper is lying 45 degrees off the vertical. If it was 60 degrees off vertical (ie. 30 degrees above horizontal) then you would get 50% of the spring
rate acting vertically. At 30 degrees off vertical you would get 86.6% acting vertically.
Obviously it is better to have the shocker as vertical as possible otherwise you need stiffer springs for a given chassis weight and will place more
loads on your suspension and shocker mountings as a result.
Cheers,
Craig.
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stephen_gusterson
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| posted on 21/1/04 at 01:10 AM |
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no, well added craig. I said it was only approx! I know from a practical standpoint that once I mounted my shocks at a more vertical angle, i could
back off the preload a lot to get the right ride height
atb
steve
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craig1410
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| posted on 21/1/04 at 01:18 AM |
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Steve,
Yes I know you were only approximating and I'm glad you took my correction in the way it was intended 
I meant to say last time that I have 275lb 8" springs in the front and even with minimum platform height it can keep my Rover V8 engine at a
decent ride height. The Pinto is a bit heavier than the V8 I think so 300lbs would seem to be fair as long as the dampers are mounted on the side of
the upper chassis rail rather than underneath. If they are underneath then perhaps a bit more tension would be required. Here's a piccy of my
setup:
Cheers,
Craig.
[Edited on 21/1/2004 by craig1410]
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Alan B
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| posted on 21/1/04 at 03:01 AM |
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Actually guys it's even more involved than that...because yes at 45 degrees the effective rate of the spring is around 70%....but the actual
wheel rate is different because of the angles too...
Allan Staniforth explains it well in most of his books, but the sine calc is pretty close....
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nick205
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| posted on 21/1/04 at 08:45 AM |
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If it's of any use the front springs on my Protech dampers supplied by MK for my Pinto'd Indy are 350lbs.
They are fitted at a fairly shallow angle, approx. 40~50°.
HTH
Nick
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stephen_gusterson
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| posted on 21/1/04 at 10:29 AM |
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f&*ing suspension is always a minefield, isnt it.
someone sometime thought 'would be a great idea to have springs on this stagecoach to give a less bumpy rid when we hit a rut or
rock'.
little did the gits know what they started 
atb
steve
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dblissett
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| posted on 21/1/04 at 06:41 PM |
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thanks lads i am now more confused than when i asked the question!!!!! ha ha
because my chasis is a 442 the shocks will be at a shallow angle so i think i will start at 325lb spring and take it from there
thank for the help dave
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dblissett
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| posted on 21/1/04 at 07:46 PM |
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whoops
as usual i have got it arse about face because i have built a 442(+2 on the height) the shocks will be at a steeper angle so should i try 300lb
springs
cheers dave
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Stu16v
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| posted on 21/1/04 at 09:51 PM |
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Dave, you still have it arse about face mate.
Unless I am confused by your last posts....
quote:
Obviously it is better to have the shocker as vertical as possible otherwise you need stiffer springs for a given chassis weight and will place more
loads on your suspension and shocker mountings as a result.
Or to put it another way, 300lb springs mounted vertically will hold more chassis weight than the same springs if mounted @ 45deg, for example.
HTH Stu.
[Edited on 21/1/04 by Stu16v]
Dont just build it.....make it!
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dblissett
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| posted on 22/1/04 at 10:00 PM |
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?
steve
if i understand it
as the shocks get steeper the spring rate can come down
ie indy and avon shallow angle 350lb springs
more upright locost 300lb ish for the same weight engine
so my pinto is getting 300lb springs to start?
the more i learn the less i know
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craig1410
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| posted on 22/1/04 at 10:36 PM |
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Dave,
You are correct!
I think the confusion may come from the wording. When you say "steeper" angle, I think that some people may visualise this as farther away
from vertical. It's one of those terms where perception's can be different I think.
Anyway, you are correct that the closer the damper is aligned with the force of gravity (ie Vertically), the less spring strength is required. 300lbs
seems to be reasonable to me but bear in mind that the free length of the spring is also important.
It might be possible to be a bit more scientific if you were able to estimate or measure your corner weights and then work out the difference between
the spring's free length and the length it would be at ride height when fitted to the damper. If you then know the angle at which it will be
mounted with respect to horizontal you can use the following formula to work out spring tension:
SpringPoundage = Wc / ((Lo-Lr) x Sin(a))
where Wc=corner weight in pounds
a = angle between damper and bottom wishbone (ie. 90degrees is vertical)
Lo is spring free length and Lr is spring length at desired ride height (both in inches)
Someone please check my sums!
HTH,
Craig.
[Edited on 22/1/2004 by craig1410]
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stephen_gusterson
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| posted on 22/1/04 at 11:31 PM |
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the more they lay down, the less the effective rating.
atb
steve
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Simon
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| posted on 23/1/04 at 09:49 AM |
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Just to confuse matters even more, as the spring is compressed the relative angle of mounting decreases, and spring rate increases
Or shouldn'r I have said that!
ATB
Simon
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dblissett
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| posted on 23/1/04 at 07:43 PM |
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thanks
so in the end it will still be a bit of a trial
so i will start with 300lb 10.5" long springs and see how it goes
as i have ride height adjustment i hope to be some where close and use the adjustment for the final tuning
thanks for the help
dave
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JoelP
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| posted on 23/1/04 at 11:10 PM |
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thats my reconing too, bodged the brackets and fix it when its all put together! Hopefully the wishbones will be level at the right ride height.
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craig1410
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| posted on 24/1/04 at 11:59 AM |
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Joel,
If you know which dampers you will be using before you fix the brackets then it is very easy to put the brackets in the right place first time without
any bodging. Spring rates are a bit of guesswork due to the uncertainty over corner weights etc but ride height is easy to predict.
I did it by drilling a piece of 3/4" square tubing with two holes exactly the correct spacing for the ride height I needed. I used GTS Tuning
dampers and Darren has a PDF drawing of these on his website with recommended ride height positioning as well as the minimum and maximum stroke. (Note
that the recommended ride height is not necessarily in the middle of the two extremes.) You then weld your lower wishbone shocker bracket in place,
bolt it to the 3/4" drilled tube and bolt the shocker top bracket to the other end. Now set your car to desired ride height (think carefully
about this mind) and then see where the top shocker bracket hits the chassis. I would recommend just firmly tack welding at this stage until you have
your dampers and springs to ensure that you have enough clearance between the spring and the top wishbone.
Also bear in mind that theoretically the best lower wishbone position is with the outer balljoint centre level with the suspension pivot point centre.
This is not usually the same thing as having the wishbone itself level and it will tend to slope upwards towards the chassis slightly.
My view on all the above is to set everything as close to "perfect" as possible within the parameters of the Locost design and within my
own abilities (and without spending too much time on it). Then I have half a chance of getting a decent car at the end of the project. This is
especially important with things which aren't so easy to change later unlike the springs which can be easily changed.
HTH,
Craig.
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JoelP
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| posted on 24/1/04 at 01:39 PM |
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cheers craig, i've already done mine though! just meant that once the engine is in i'll adjust the platform to get it right again! thanks
anyway.
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craig1410
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| posted on 24/1/04 at 02:07 PM |
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Joel,
Yes as long as the spring rates are "close enough" then the platforms should be able to take up any minor adjustment. I think the only
problem may come if the springs are way too light in which case you'll end up with coil binding under bump conditions due to the platform being
so far up.
Cheers,
Craig.
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pbura
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| posted on 24/1/04 at 02:19 PM |
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One technique I've seen here and there is to build initially with "shocks" made of 1" tube drilled at the ends for proper ride
height.
Then, after the car is otherwise built up, weigh the corners and you will be able to initially spec the springs a bit more precisely.
Pete
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Stu16v
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| posted on 24/1/04 at 06:39 PM |
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Sorry Dave, I've just re-read your posts, and with Craigs translation, you were thinking the same as me.
I shall confuse you (and myself) no further
Dont just build it.....make it!
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