Date:         Tue, 30 Jun 1998 13:09:33 -0400
Reply-To:     Don Gibbons <dgibbons@PRESRAY.COM>
Sender:       Vanagon Mailing List <Vanagon@vanagon.com>
From:         Don Gibbons <dgibbons@PRESRAY.COM>
Subject:      Springs and spring rates
Comments: To: vanagon@vanagon.com
Content-Type: text/plain; charset=US-ASCII

Alot of this stuff flying around concerning springs is just wrong.

If you put spacers in between the spring coils you WILL raise the ride height
slightly. You will also reduce the number of active coils in the spring. The
equation for the spring rate of a coil spring:

k= d^4 G/8 D^3 N

d is the wire dia, D is the mean spring dia, G the modulus of rigidity, and N is
the number of active coils.

Placing a spacer (rubber or otherwise) in the spring will create a slight
"preload" in the active part of the spring. It will also make the spring rate go
up.

The stress in a spring:

stress = K 8FD/pi d^3

K is a correction factor, and F is the force on the spring.

So you put a number of spacers in the spring. This make the spring rate go up.
This means that for a given bump or spring deflection the force in the spring
goes up too. This makes the stress go up just as well. Not good.

The relationship is linear. Reduce the number of active coils in the spring in
half, the spring rate doubles and the stress also doubles. This practice may be
OK for racing where the parts can be inspected after only a few hours use. Most
racing classes that allow spring adjustments do it by adjustable spring perches,
not spacers.

Spacers are not the thing to do if you have hundreds of miles to cover off road
or only look at your springs every 3 months.












Pawling NY

Cars I have: 93 Eurovan MV
                  75 Westy
                  73 Super

Cars I had: 89 GTi 16v
                 87 Syncro
                 83 Rabbit GTi
                 82 Vanagon Diesel (w 83 GTi engine)