Effect on coil spring rate from rubber mounts
Effect on coil spring rate from rubber mounts
(OP)
We're trying to decide whether or not to add rubber bushings on the top of the front coil springs on a vintage Alfa Romeo race car. The rubber bushing is stock and has some practial advantages, not related to the spring rate.
I've read and been told that adding a rubber mount to the top of racing coil springs will severly reduce the overall spring rate. But I wonder how it can have much of an effect when considering a rubber mount that is about 3/4" thick and likely compresses less than 1/4". In my application the coil springs compress about 3" during full suspension travel. The spring rate is 1250#/inch but I have no information on the rate of the rubber. Can someone clear this up?
Curt Griggs
I've read and been told that adding a rubber mount to the top of racing coil springs will severly reduce the overall spring rate. But I wonder how it can have much of an effect when considering a rubber mount that is about 3/4" thick and likely compresses less than 1/4". In my application the coil springs compress about 3" during full suspension travel. The spring rate is 1250#/inch but I have no information on the rate of the rubber. Can someone clear this up?
Curt Griggs
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RE: Effect on coil spring rate from rubber mounts
In your case the steel spring will be significantly softer than the spring mount, by about a factor of 12 if your measurements are right (they seem reasonable).
So in your case the net effect will be a drop in spring rate by 8%. This will be offset by the extra length of the toal assembly, so your ride height will /increase/, which may be the cause of your informant's comment.
Oh, remember that compliance is the inverse of rate, a source of endless confusion.
Cheers
Greg Locock
RE: Effect on coil spring rate from rubber mounts
If the system is two springs in series:
Ktotal = ((kroad spring)-1 + (kmount)-1)-1
You must also note that those mounts are highly non-linear.
Best regards,
Matthew Ian Loew
"Luck is the residue of design."
Branch Rickey
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RE: Effect on coil spring rate from rubber mounts
Curt Griggs