RE: Springs and all that (long)

["Brian Shorey" <bshorey@xxxxxxxxx>]

> Following up on the spring thread:
>
> >>>And I recall a comment that if you cut a spring, then the car
> might raise-
> >>>this is NOT true.  Yes, the spring rate increases linearly
> with the number
> >>>of coils lost, but the rest height goes down the same amount...
>
> >>Been there, done that. Don't agree, sorry.
> >>Car - 2 litre Giulietta (Nuova). Rear springs cut too
> conservatively (owner
> >>was cautious). Ride height went up - measured before and after! My
> >>interpretation was spring became stiffer and harder to compress for the
> >>same load and therefore the deflection was insufficient to lower the car
> >>even allowing for the lost length. The springs were new.
>
> >I don't believe there's any way you can cut metal out of a spring, put
> >it back in the car, and have the car sit higher, assuming all the other
> >parts went back in the same place.  When measuring the effect of ride
> >height changes however, it's best to disconnect the shocks.
>
> I was also skeptical initially, but if Les says it happened I'll believe
> him! I think that I know why, and even got keen enough to do the maths to
> (more or less) support my hypothesis.
>
> The key to it is the shape of the ends of the springs. The last coil or so
> is flattened (has much shallower helix pitch) than the rest of
> the springs,
> so typically the free end is not very far away from the next coil. However
> (as I found when testing my spring) most of the last coil is still active,
> even when compressed against the spring seat (the spring works in torsion,
> not bending, and can continue twisting even when in contact with
> the seat).

still catching up, was there ever a definitive conclusion to this?  all of
the above makes *no* sense whatsoever to me.

cutting a spring will increase the spring rate.  cutting a spring will
decrease the spring length, under any and all loading.

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.

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?

should i throw out my physics books?  anybody?

bs

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