RE: Springs and all that (long)

["Brian Shorey" <bshorey@xxxxxxxxx>]

> > if i've got a spring with 10 coils in it, and cut one off
> either end, the
> > resulting spring will be shorter.  if i compress the before and after
> > spring, the middle eight coils of the before spring will be the
> same length
> > as the middle eight coils of the after spring,  and the before
> spring still
> > has a coil at either end.  the before spring has to be longer.
>
> BUT, the middle eight will not be the same length as they used to be:

huh?  what law of physics causes them to get longer?

> some of the ends of the eight will be inactive, so the eight coils

inactive?  why?  the only section of a spring that would be 'inactive' would
be one that is perpendicular to the center line of the spring.  unless i
flatten an end of my cut eight coil spring, the entire length of the spring
will contribute to the spring rate.

> will be slightly longer than they were. Yes, the same applies to the
> original 10 coil spring, however this had the last coil flattened
> off at each end (which was the coil that was removed). The length
> (height) of the inactive region will be greater for the 8 coil spring
> than that of the 10.

again, why?  this seems counter-intuitive to me.

> I believe that because of the flattened ends of
> the orginal spring the length will not reduce as quickly as the rate
> increases.
>
> What actually happens depends on the geometry of the particular
> spring. My (very crude!) calculations indicated that this behaviour
> is only likely for springs that are relatively long with a shallow
> helix angle, such as a 105 or 116 rear springs. In my tests on a
> front 105 spring even with only half a  coil removed the loaded
> length reduced, and with 1 coil off  I got a  20mm reduction in
> loaded length as predicted. I'd like to test a rear spring to see
> what happens.
>
> As a side issue the behaviour at the end of the spring is one of the
> potential problems with cutting springs. The load transfer from the
> car to the spring is not as gradual as it would be originally which
> has the potential to cause local overloading of the spring or car
> spring seats, again depending on the geometry and materials of each.
> Cutting one end rather than both seems wise to me: at least this
> problem (and any instability) will be only at one end.

this is true.  properly cut springs, imho, should have the ends tempered and
flattened.  in addition, care should be taken when removing less than a full
coil, to make sure that the ends line up properly with the recess in the
seats.

>> however, if i cut a spring and then add a spacer of equal thickness of
the
>> amount  of the spring that was removed, then the ride height would be
>> higher.  perhaps this is what les was alluding to?
>You're correct, but it wasn't from what he's told me.

however, there's also the chance that the cut spring wasn't seated the same
way the uncut one was seated.  you could change the ride height of a car by
rotating the spring such that it's not seated properly.

the whole concept of a shortened spring raising a ride height still makes
absolutely no sense to me.  mr grinch, whom i suspect is still aware of what
goes on in the digest, must be raising an eyebrow over this one..

bs, who relies on the capabilities of mr ward, mr dean, mr shankle, and mr
glynn for setting up his suspension(s).

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