Question for the Suspension Gurus
Discussion
I recently had the S in for a major service, and the mechanic pointed out that the springs on the n/s of the car were upside down. He opined that they had probably been fitted like that at the factory. As some work was being done on the front corners anyway I asked them to put the springs on the right way round. (They are 'rising rate' type with close coils at the top.)
Having had this done, it feels that the ride is a little less 'crashy' than before or is this a figment of my imagination? Logic would tell me that the force required to compress the spring would be the same irrespective of which way round the spring was fitted, but is this actually the case?
Look forward to the responses.
Cheers
Graham
Having had this done, it feels that the ride is a little less 'crashy' than before or is this a figment of my imagination? Logic would tell me that the force required to compress the spring would be the same irrespective of which way round the spring was fitted, but is this actually the case?
Look forward to the responses.
Cheers
Graham
Mine had the close coils at the top too, and I always kept the springs that way up, but I can't see that it would make any difference to the spring rate which way up they are? In theory it means the unsprung portion is lighter too, but the numbers involved are way too small to be worth bothering with. There may be some more practical reason, like getting better ventilation (cooling) round the damper or being easier to fit the spring compressors? But my guess is it is purely cosmetic.
A rising rate spring should be orientated the right way round (close coils at the end of the damper stroke / top) as when a spring goes coil bound (all coils touching) it's spring rate massivly increases (effectivly iron bar spec). So you can see if you compress the spring and it starts to bind only a couple of coils then the spring rate will start to increase. Admittedly a spring should deform uniformly along its length but often this isn't the case and small movements will only move the first couple of coils and to cover these scenarios I'd fit the springs the way Pete says.
Count yourself lucky I don't think you can get rising rates for a wedge
Matt
Count yourself lucky I don't think you can get rising rates for a wedge
Matt
quote:
Yebbut you are compressing a spring from two points which are the ends so how can the amount or the manner in which a spring is compressed be affected by it's orientation?
Mark
Basically you're right. The law of physics say it doesn't matter. The rising rate spring is theoretically two different springs in series, not in parallel. One of this springs has the stiffness (on compression) of a steel bar. Above said comes true, if the rising rate spring gets compressed at 100%
inline with the imaginary middle axle of the spring, which I doubt is the case on the car. I haven't had a closer look at the kinematics of the suspension, but I think, that the lower part of the spring has to follow an arc, as a function of the lower wishbone movement. The upper end does not need to do so. The lower end needing to do a small lateral movement(to follow the arc movement of the lower wishbone) results in additional flexion of the lower part of the spring. This might as well explain, while the ride is more crashy, when the blocked windings are downside. They can't take that additional flexion
BTW, my car came with the blocked windings on top, as well.
Cheers Patrick
Graham,
Sorry for coming a little late on this one but I've just been going thro' an old Burton Power catalogue and in their suspension section there is a tech tip which reads "Progressive coil springs are designed to give progressively higher spring rate the more they are compressed. When fitting always fit the closer wound coils at the top". It doesn't explain the why but certainly confirms you've done the right thing in changing them to this orientation.
Hope that's of use.
Chris Page
Sorry for coming a little late on this one but I've just been going thro' an old Burton Power catalogue and in their suspension section there is a tech tip which reads "Progressive coil springs are designed to give progressively higher spring rate the more they are compressed. When fitting always fit the closer wound coils at the top". It doesn't explain the why but certainly confirms you've done the right thing in changing them to this orientation.
Hope that's of use.
Chris Page
quote:The spring is held by the shock which can't bend and the shock is bushed at the top and bottom so no matter what compression is on the spring it is always being compressed in a straight line directly down the length of the spring. Therefore it wouldn't matter whether it's the 'right' way up or not in terms of how it would affect compression.
I haven't had a closer look at the kinematics of the suspension, but I think, that the lower part of the spring has to follow an arc, as a function of the lower wishbone movement. The upper end does not need to do so. The lower end needing to do a small lateral movement(to follow the arc movement of the lower wishbone) results in additional flexion of the lower part of the spring. This might as well explain, while the ride is more crashy, when the blocked windings are downside. They can't take that additional flexion
My guess is that possibly the springs can move around if installed the wrong way up whereas they can't if they are installed as recommended. Or maybe that if the blocked windings are on the bottom where they are more exposed to the road crud then there is a higher chance of stones or debris being trapped in the closer windings than if they were on the top.
Just my 2p.
Mark
>> Edited by mhibbins on Tuesday 19th March 20:55
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