02GF74
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| posted on 9/8/14 at 11:50 AM |
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advice on spring selection
background: formula 27 kit car fitted with triumph dolomite rear suspension which is far too hard.
I have found 2.5 in coils (65 mm) that may fit (so no need to get the grinder out!"
Free length of my coils is: 291 mm (11.5 in)
I cannot get the exact length so which will be the better choice (spring seats are non adjustable)
10.5 in (267 mm) or 12.0 in (305 mm)? (24 mm shorter or 14 mm longer)
What would be a suitable spring rate for road use?
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rusty nuts
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| posted on 9/8/14 at 11:55 AM |
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Convert to coil overs? I wouldn't be surprised if the strings have become compressed with age so it may be that the longer spring is the ones
you need provided you can get it compressed to fit ?
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02GF74
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| posted on 9/8/14 at 12:22 PM |
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Length of spring fitted with wheels on the ground is 240mm (9.5".
If f I jack up one wheel, the difference in spring compression as measufed by gap between tyre and arch - s small, in region of 5 mm , surely that is
far too small indicating springs are too hard.!?!?!!???!!????!!!???
Spring rate anyone?
I have rear axle weight noted is there a way to work it our allowing weight of driver and passrnget?
[Edited on 9/8/14 by 02GF74]
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Sam_68
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| posted on 9/8/14 at 02:37 PM |
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quote:
Originally posted by 02GF74
Spring rate anyone?
I have rear axle weight noted is there a way to work it our allowing weight of driver and passenger?
If you know your corner weights, you can work out the spring weight by measuring the length of the spring when the weight of the car is sitting on it,
on level ground (you may need to put the car on ramps to gain sufficient access to measure the spring), then subtracting that from the free length of
the spring. That gives you the compression.
Just divide the spring compression measurement into the corner weight of the car, and hey presto, you have the spring rate!
Alternatively (though rather less accurately), take the spring off and measure the length with you (or a similarly hefty known weight) standing on it.
Divide the spring compression into your weight from your bathroom scales, and you have an indication of the spring rate. For example, I'm a fat
bastard at about 230lbs, so if I stand on a spring and it compresses by 1.35", the spring rate would be 230/1.35 = 170lbs/inch.
Note that 'spring rate' is not the same as 'wheel rate', though... you'll have to take some more measurements and figure
out the leverages for that.
I agree with Rusty Nuts, though... the only proper way to deal with the problem is to fit dampers with adjustable spring seats. The odds are
against you finding a spring of the right rate and length to give you exactly the right spring rate and ride height you want, whilst working with the
dimensions of your fixed seat dampers and the measurements of the chassis and axle mountings. But even if you fit some adjustable dampers, you would
still be wise to do some rough sums to work out approximately the right free length of springs you need to suite the dampers lengths at normal
ride height.
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alfas
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| posted on 17/8/14 at 08:38 AM |
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quote:
Originally posted by 02GF74
If f I jack up one wheel, the difference in spring compression as measufed by gap between tyre and arch - s small, in region of 5 mm , surely that is
far too small indicating springs are too hard.!?!?!!???!!????!!!???
[Edited on 9/8/14 by 02GF74]
i rather think that "something" else is limiting the described gap:
either your shocks are already fully expaned or the axle might already touch a chassis-tube and therefore limiting the travel of the shock.
best you post a pick of your actual arrangement.
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