King spring said stock was 110lb and they use 140lb with their lowered set for coupe/sedan

this although lwd ute should help - pics also before & after
http://www.south-yokohama.com/products/detail.php?product_id=29

translated
http://www.microsofttranslator.com/bv ... /detail.php?product_id=29

Factory B120 Service Manual extract.

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according to that the spring rate is 149lb/in for the standard leaf spring, and 203lb/in for the option spring, assuming linear rate.
That confirms the B120 info in the wiki, apart from the comment about "on overrider".

"the overrider" is the 13mm thick leaf mentioned at the bottom of the list.

yes, but it doesn't confirm it is on the overrider at 4" of compression from full droop. It probably is, but it doesn't confirm it. If it is on the overrider, then that spring rate is complete nonsense - it would be something less than that at normal height, and something more when it is actually on the overrider. Hence the proviso "assuming linear rate". Its only a linear rate spring (and therfore only a meaningful spring rate) if the overrider is not involved at that compression.

Yeah it would be interesting to know for sure, I would say its alot closer to being 267kg/mm, 149lb/in rate than the coupe figure of 110lb/in. Just from memory the overrider doesn't come into play till the bump stops are nearly touching the chassis. Did a rough measurment, starting with unladen ride height, adding 80kg of weight to top rail centered longitudinally, above the axle centerline. Ride height dropped by 22mm. Taking into account friction and binding caused by the leaves sliding against one another, I would say it fairly accruate as at 80kg for 22mm droop that is over the spec given. The coupe leaf thickness in wiki however of 1x6mm and 2x7mm thickness would suggest different, however they have less free camber to start with which would cause a flatter leaf profile.

Latest reply from Mark,

"Hello Joe,

Some more info on the free arch height specifications: We use a total of 4
different arch configurations, but for small, light applications like this
two of them will work. The main things we need to know are what the arch
height of the current spring is and what, if any, change in ride height is
desired. Then, the rate and some idea of the vehicle's static weight factor
in.

A combination of a little simple math and our experience with getting ride
height right determines what we do. Here's an example using some of the
specs you've sent previously.

If the current spring has a rate of 109 lb/in there would be 3.2 in. of
spring compression with the spring loaded under the static weight of the
vehicle:

(46% X 1532 lbs) / 2 springs divided by 109

If we replace this with a 140 lb spring, the ride height will be increased
by .68 inch:

3.2 - (352.36 / 140)

That is really close to what the reduction in arch height would be with a
reversed rear eye, thus my comment about reversing the rear eye when we make
the springs. The compression of our spring under static loading of about 2.5
in. also tells me that our low arch blank would work.

If your truck has 203 lb/in original 5-leaf springs, 225 to 240 lbs in our
springs should feel about right.

Bolt sizes are often different front & rear, so don't be surprised by two
different sizes.

Mark"

Quote:

hmmm, that indicates exactly 203.2lb/in
EDIT: doh, divide that by 2 = 101.6lb/in
that's softer than what we're told the standard sedan/coupe spring rate is.

It seems that we will have to add on 20-30 lb/in to achieve stock results with a composite leaf. Any lower might be too soft..I think the official stance is composite leaves are 20% softer at any given rate of a steel spring.