BOMBARDIER 1996 Ski-doo MX Z440 Handbook page 24

Section 03 CHASSIS PREPARATION
300
200
STRAIGHT RATE = 100 Ibf /
AOIFILS
An easy way to measure coil springs is to put a bathroom scale in a press with the spring resting on
the sca-le. Measure the free Iength and then apply a load until the 'spring compresses-l inch. The
reading on the scale will approximate the rate of the spring. Now compress the spring another
1 inch. If the spring is a straight rate, the scale reading should be doubled. If the reading is more
than doubled, then you have a progressive spring. If you can compress the spring another 1 inch
(3 inches total) (don't blow Up your scale) the reading should be 3 times your first reading. In order
to maintain a reasonable cost on springs, the manufacturing tolerances are quite large. A 100 lb/in
rated spring may test anywhere from 80 to 120 lb/ in.
Now, so far we have assumed that the 2 springs in our examples have the same free length and
that they are not preloaded at all. In the case of our suspensions, we mount the coil springs on a
shock absorber. The shock will have a certain length between the spring retainers which is called
the installed length of the spring. If the installed length is less than the free length (as is the case in
most applications), then there will be some preloading of the spring.
at 8 inches. We will put them both onto a shock with an installed length of 7 inches. The 10 inch
spring will need to be compressed 3 inches. This will give us a preload of 300 pounds. The 8 inch
spring is only compressed 1 inch so it only has 100 pounds of preload.
03-8
100
A
in
150
. .
A A
PROGRESSIVE RATE = 100/ 200 Ibf /
450
300
in