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Thread: Rear spring rate

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    Rear spring rate

    Anybody use unassisted coil rear suspension on their nova, what spring rate are you using? , I've calculated I need around a 4.5k/250lb spring not to hard not to soft

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    ***Euro-Nova Supporter*** BlueNova's Avatar
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    Quote Originally Posted by Mikemrb View Post
    Anybody use unassisted coil rear suspension on their nova, what spring rate are you using? , I've calculated I need around a 4.5k/250lb spring not to hard not to soft
    Iím pretty sure that Lauren should be able to help you with that one Mike

    Alistair

  3. #3
    Mark and Jim both had unassisted coil overs using Red 9 kit, and both experimented with various springs before they got to something they were happy with. Hopefully they can chime in and remind us what they ended up with. I'm also interested as I have the same set-up, albeit it hasn't been on the road yet.

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    Quote Originally Posted by islandman View Post
    Mark and Jim both had unassisted coil overs using Red 9 kit, and both experimented with various springs before they got to something they were happy with. Hopefully they can chime in and remind us what they ended up with. I'm also interested as I have the same set-up, albeit it hasn't been on the road yet.
    Thanks David
    I know I'll have to experiment, also mine will be a little bit different as it's transverse mid engine so most of the weight in front of the rear wheels, I've calculated it but as I've had before with my tarmac rally car there's nothing like the feel of the car to get it how you want it to handle and comfort of the ride, the coilovers came with 8kg springs which are going to be rock hard
    Mike

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    ***Euro-Nova Supporter*** Spacenut's Avatar
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    You are using struts I think Mike? I made up a spreadsheet to calculate spring rates using the formulas in Allan Staniforth's Race and Rally Sourcebook, which I guess you must have seen before. My personal version was for double wishbones all round, where I found 325 lb springs to work best, but of course with struts the spring bears directly on the end of the lower wishbone so a lower spring rate is appropriate.

    I have adapted the spreadsheet to deal with coil-assisted torsion bar IRS (for Nova Nigel) and coilover IRS conversion (for Giles Briggs). For the latter I still needed 325 lb/in to achieve the target natural frequency of 120 cpm, although I believe Giles went for a softer spring in the end. I started off with 250 lb springs on the back of my car so it will definitely keep its backside off the road

    Are you using an anti-roll bar in your design?

    Lauren
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    ***Euro-Nova Supporter*** Spacenut's Avatar
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    I should point out that Giles' Nova uses the iron-block engine from the Alfa 33, and my calculations also had to account for the rear mounted water radiator. So probably approaching the mass of the Busso V6...

    Nova Nigel's car needed 80 lb helper springs to boost the effective rate of the torsion bars, which I seem to recall were 125 lb/in. It was only several years later that I saw the Wheeler Dealers 944 track day car episode, where Brewer had to buy a Grands worth of suspension parts to do the same job! My calculations suggested 110 lb springs on the front of Nigel's car would be optimal, but only 100 and 120 lb increments were available so Nigel selected the firmer of the two. The jiggling you see on my "2 Novas 2" video is due to the 120 lb springs. Nigel later switched to 100 lb and the ride was much improved! I went out for a couple of runs in Nigel's car after he had completed the suspension work and we both agreed that the handling and ride were really good for a car of this type.

    Lauren
    only Pythagoras can save me now!

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    Quote Originally Posted by Spacenut View Post
    You are using struts I think Mike? I made up a spreadsheet to calculate spring rates using the formulas in Allan Staniforth's Race and Rally Sourcebook, which I guess you must have seen before. My personal version was for double wishbones all round, where I found 325 lb springs to work best, but of course with struts the spring bears directly on the end of the lower wishbone so a lower spring rate is appropriate.

    I have adapted the spreadsheet to deal with coil-assisted torsion bar IRS (for Nova Nigel) and coilover IRS conversion (for Giles Briggs). For the latter I still needed 325 lb/in to achieve the target natural frequency of 120 cpm, although I believe Giles went for a softer spring in the end. I started off with 250 lb springs on the back of my car so it will definitely keep its backside off the road

    Are you using an anti-roll bar in your design?

    Lauren
    Hi Lauren
    yes coil over struts which I'll re-machine the spring cups to take 2.25 id springs as there seems to be a lot more rate choice in that size, Iíve done a recalculation, I didnít factor in the motion ratio correctly as the strut mounting on the lower wishbone is 100mm in from the ball joint so would make the 250 lb to soft, it works out close to your spring rate so will give me a starting point, Iím using an anti-roll bar if I can find one narrow enough and make it adjustable so I can play with the understeer /oversteer
    mike
    DSC_0465.jpg

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    My rear set up was swing arm red9, which was the same as Mostins.
    I had to modify all of my shock lengths to get the right height and my springs were also 1.9 , not what you are going for.
    Faulkner springs are really helpful and can make customs springs, which are expensive however !!
    It seems you already know the direction you are going , but it took me at least 4 sets of springs to get it right for my car......

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