gas shocks, springs & ride height

[<CARIBOULH@xxxxxxx>]

Kelly M. wrote in Alfa Digest #47 recently...

<<>>

 Kelly, 

The springs alone are probably not responsible for your car's height increase,
but believe it or not the KYB shocks deserve as much credit (blame?) too. When
you replace shocks on a car originally designed for conventional hydraulic
shocks with gas pressurized shocks you will raise the car's ride height. With
everything else functioning normally and at rest, a car's ride height with
hydraulic shocks OR without them installed does not change. The springs
support the weight of the car, not the shocks. But when you install gas
charged shocks, the charge of the gas inside is always trying to make the
shock expand. That's why they have those straps on them in the box... remove
the strap and they expand instantly.

You could measure the force of expansion easily with an accurate bathroom
scale; put a fully expanded shock on the scale and press down on the piston
rod until you get it to move a few inches than stop and hold it in place, read
the scale. If it reads, say 40 pounds, that's the force that shock when
installed on the car will be trying to LIFT UP that corner of the car with (by
trying to expand when it's installed). If you go to the corner of your Spider
and try to lift up on the bumper with a 40 pound pull I won't be surprised if
the car raises a bit... would you? Well, when you install gas shocks on your
car that is what's happening all the time. The shocks are trying to push the
car up! Please note: the 40 pound force I am referring to is for purpose of
example only. I don't know what the force on the KYB's actually are. I just
tried one of the Gabriel gas shocks that we here at Caribou have made up for
Fiat Spiders and measured 34.4 pounds to hold the shock steady from expanding
on our very accurate digital shipping scale in the warehouse. I would guess
the KYB's are in the same ballpark.

So, put 4 KYB's on your car and it is the equivalent of having maybe 140 to
160 pounds of force (4 shocks times maybe 35 to 40 pounds of expansion force
per shock) pulling your car upward! It's no wonder that your car is higher now
than it was before! My guess would be that if you had not replaced the springs
at the same time, but just done shocks that you would have noticed and even
greater increase.

For those of you who are curious, the converse is true. Take a car DESIGNED
for gas shocks (Porsche or BMW or MBZ must have one) and when you remove the
gas shocks the car sits lower than normal ride height because the engineers
designing the car included the shock's force trying to raise the car in their
calculations on how that would affect the other suspension components and
accounted for that when figuring the ride height.

Best Wishes,

Ed at Caribou Imports, Inc.
NOW... the largest Fiat parts supplier in the Western U.S.
visit us on the Web at:
www.caribou.cc
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