Sooo. after looking for the pound/inch rating of the 4 coil springs in the rear of a Jaguar xke in many books, spec sheets on springs, and internet sites, I could not come up with definitive values for these springs.
The after market use of the Jag rear cage set-up in hot rods and Cobras have all kinds of suggestions for their purposes but no information on what a XKE comes with ! Before you can lower or raise the ride height or increase or decrease the stiffness of the springs you MUST know the original starting point!
My 1971 E-Type (sept 1970) needs to be lowered 1 1/4" at the rear so by me buying Coil/over adjustable shock/springs I will have to have to have springs
1 1/2" shorter than mine, which are 11" so I would need 10" rear springs.
This will give the desired ride height (from 1 1/2" lower to 1 1/2" higher than stock with the adjusters). BUT what rating do you choose? So I set-up
a spring inch pound measuring device (see pictures) with this device I was able to measure the inch of squeeze and the pounds on the scale to get to one inch ! Stock XKE springs are 175 to 185 pounds inch, this was verified with many springs and many scales. BUT what was also noted is the spring
when mounted on the stock Jaguar shock is preloaded or squeezed down by
the shock by an 1 1/2". The mounted spring is now 9 1/2" long, which means at this point it is already under compression of 270Lbs !
So 4 springs at the rear of your Jag at 270lbs times 4 =1080lbs If all this sounds to soft remember the shock/springs are mounted inboard and at an angle this reduces their capacity by 20% or down 866lbs. Put the real weight of the rear of the car on these plus the stresses of hard driving it is easy to see why some guys go to 250inch/pounds or more for their springs !
If all this sounds confusing remember your starting point 175 to 185inchlbs
on an original spring......... Not mounted, not squashed, not preloaded,
so when buying springs that are going to be shorter than original you now know what to choose !