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Oct 27, 2009 13:41:15 GMT
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Finally after a lot of trial, testing, modding, rebuilding, further testing & modding, I have my finished coilover strut bodies for project Rascal. HOORAH!! The next step is to get some appropriate springs for them. This is where I am completely stuck! Where to I start?? Basically, the Rascal will be dropped as low as it can possibly go (not as far as I'd like due to clearance issues) but what rate springs do I need to go for?? This is for the front springs/coilovers, the rears will be dealt with once I get the front sorted. The weight of the vehicle is 785kg (according to the interweb) with a fair bit of that weight being over the front wheels. Does anyone have any idea where I start to work out what spring rate to go for?? I obviously need it to be firmer than the original springs, but not so harsh that I need one of these when I drive down the road:  Many thanks for any help/advice given..... ;D |
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Oct 27, 2009 13:45:27 GMT
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Remember it depends on the actuation ratio - Macpherson struts are usually 1:1, other setups may differ.
I had 175Lb springs in my Lupo (which weighed slightly more over the front) and the ride was firm, but acceptable.
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Oct 27, 2009 13:53:30 GMT
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Thanks Cobblers,
I'm afraid you lost me at 'actuation ratio' though - I'm not too clued up on the physics of suspension to be honest!
My google-fu is weak today, looking it up only comes back with stuff about bike derailleur's!
I'd imagine a Lupo doesn't weigh an awful lot more than a Rascal, so do you reckon I should be looking around the 170lb mark then or am I getting this completely wrong?
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stealthstylz
Club Retro Rides Member
Posts: 14,842
Club RR Member Number: 174
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Oct 27, 2009 13:57:24 GMT
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The bottom suspension arm is a lever. On a Mac strut the spring is about as far from the inner pivot point as possible giving nearly a 1:1 ratio. On a double wishbone front end the coilover can sometimes be mounted half way along the bottom arm giving a 2:1 ratio, meaning you need stiffer springs as there is more leverage on them.
Matt
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Oct 27, 2009 14:02:31 GMT
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AHA!
Thanks Matt.
Mine is a strut with a single lower suspension arm so I'm guessing this means it's a macpherson strut? Next step is to work out where to start with spring rates (other than wild guesses LOL)
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markbognor
South East
 
Posts: 9,969
Club RR Member Number: 56
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Oct 27, 2009 14:13:08 GMT
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Could you calculate the rate of the original spring as well? Then you have got a figure to go up from. There's a spring rate calculator here. |
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markbognor
South East
Posts: 9,969
Club RR Member Number: 56
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Oct 27, 2009 14:19:02 GMT
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No you can't. You have no way of knowing the modulas of rigidity of the spring material.
Though I suppose you could construct some sort of experiment to see how many Lbs of weights you would need to compress the original spring 1".
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kee
Posted a lot
Posts: 4,990
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Oct 27, 2009 14:21:55 GMT
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if you just want it a bit more stiff than normal then go 150-170ib/in.
mine are 240ib up front and 350ib rear and i can barely move the curse word, not very comfortable to drive and it weighs less than a rascal. but there is no body roll at all and thats what i wanted (easier to use stiffer springs instead of modding ARB's in this case)
Choosing suspension rates is completely guess work, try to borrow some springs or just get some cheap 2nd hand ones until you find the best for the application.
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kee
Posted a lot
Posts: 4,990
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Oct 27, 2009 14:23:45 GMT
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Mark.
for calculating spring rate you can squash it withj a determined weight then mess about with calcs to find it out.
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Oct 27, 2009 15:30:06 GMT
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Thanks for the input guys.
In some ways I'm more confused than when I started, but Kee, awesome suggestion about trying some 2nd hand/borrowed ones - that sounds like a good route.
I've found a company only a few miles from me who can give me the proper spring rate of the originals (according to the guy on the phone, they've got some machine that compresses it and works the exact rate out!) which will give me a good starting point at least.
Once I get some more info, I'll be trying to work out what length springs I need....tomorrow I'll get the new struts mounted and get some measurements of fully open & ride height distance/lengths on the strut.
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kee
Posted a lot
Posts: 4,990
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Oct 27, 2009 15:33:07 GMT
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ideally ride height should be around 1/3 from bottom.
this then means there will be 2/3rds of the shock left for bump and 1/3 for rebound.
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kee
Posted a lot
Posts: 4,990
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Oct 27, 2009 15:34:13 GMT
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ALSO
don't forget that softer springs will affect the ride height due to them being compressed more from the weight.
its all a bit hit and miss unfortunately unless your fully into suspension design etc.
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rysz
Club Retro Rides Member
Posts: 2,554
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Oct 27, 2009 15:46:35 GMT
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No you can't. You have no way of knowing the modulas of rigidity of the spring material. Though I suppose you could construct some sort of experiment to see how many Lbs of weights you would need to compress the original spring 1". This might help: www.springhouston.com/mat_chromevanadium.htmThe majority of car springs are made from Chrome Vanadium spring steel as this is one of the hardest wires available especially when you consider that cost is a big factor in material choice... Rysz. |
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Oct 27, 2009 15:51:15 GMT
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Blimey - now I'm really confused! I was planning to do something like this:  Fit the strut and set the adjuster nut (lower nut that holds the spring) roughly mid-way on the height adjustment thread (A) Let the suspension 'drop' so that the suspension is fully open then measure the distance between the upper and lower spring mounts (B) Then put the car to the desired ride height and measure again the distance between the spring plates (B) This would give me the open length and ride height length.....so I know I need a spring lenght somewhere between those mesurements with room to adjust up & down if I need to. Spring helpers can then be used to take up any slack on the fully extended length. That's what I was planning to do regarding the spring lenght choice, but I'm certainly not into suspension design, so am probably thinking about everything the wrong way! LOL |
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Oct 27, 2009 15:58:08 GMT
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Any pics of a before and after of the struts?
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kee
Posted a lot
Posts: 4,990
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Oct 27, 2009 16:01:46 GMT
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that would work bruce, just maken sure there is more travel on bump than droop.  |
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Oct 27, 2009 16:01:54 GMT
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Any pics of a before and after of the struts? I'll get some pics for you tomorrow when I'm down at the unit  |
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Oct 27, 2009 16:05:19 GMT
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that would work bruce, just maken sure there is more travel on bump than droop. I take it you mean more upward travel than downward travel? The way this van will sit, there will be more of the damper shaft 'in' the strut than there will be 'out' if that makes sense?? Unfortunately, I can't change that factor without running the car at almost standard ride height!  |
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Oct 27, 2009 16:08:49 GMT
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helper springs can always take up any slack bruce so that isn't critical - still nice not to have to worry about them i spose.
my escort has 180lbs x 10" on bilstien coilovers which i fitted when running the x-flow but is still ok with the pinto in there too.
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kee
Posted a lot
Posts: 4,990
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Oct 27, 2009 16:14:58 GMT
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you got it bruce if that is the case then you need to make sure the springs are stiff enough to stop the shock bottoming outn as it could damage the valves inside the shocks. you'll probably be ok though, just whack some springs on around 160ib and see how it is |
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