Rear coil spring selection too confusing

I had in a prior post wanted suggestions for coil spring replacement. I have Gaz shocks with adjustable height perches. My nonoriginal springs are sagging on one side and have adjusted them to compensate.
These springs are 10 1/4" long with 10 coils with unknown lb. rating. Perches on one side are almost at bottom and car is sitting a little high? Mike had suggested checking out Summit for 2.5-inch x 10" 250 lbs, trying to get coil count from them? Not even sure if this is important I am trying to learn the science behind coil springs but life is too short !
SNG has two springs specifically for the Gaz shocks one 8" 325 lb. an another 8" 275 lb.
XKs also Gaz specific 9" 275 lb. Do not know how the distance of original shock extended distance compares to Gaz shocks. As above the specs are all over the place, fear is installing another 10" spring and it sits too high? If I knew the spring rating of my current spring it would help. Terry’s also offers springs over 10" long with 11 coils.

Take your original springs to your local spring works. Get them to measure the springs. They can reset them for you.

My original springs are long gone.
What I now have now were $20. springs that never were a good match. When these springs were mounted on the Koni shocks car sat too low. Now mounted on Gaz adjustable perch shock it sit too high.
Thanks Andrew, you made me think this through. I need a shorter spring I think?

Hi Glenn…SNGB currently run their demo ots 50EE with their adjustable platform Gaz and springs in the UK…the ride height looks good…why not email them and find out details of their setup…Steve

Sng offers two spring choices for the Gaz shocks, both 8" long and rated at 325 lbs and another at 275 lbs… Using a 2" shorter spring concerns me?
Thinking about ordering from Summit their QA1 high travel springs. 9" long rated at 250 lbs and made from a higher quality steel?

Hi Glenn…if your just going by the info on their website then its a bit confuseing…i have mentioned it to SNGB that the info on their website re rear shocks is very confuseing…showing gaz adjustable as front shocks etc…thats why i suggested contacting them to find out what they are actually useing on their demo ots 50EE…they use this car to trial many of their parts…I had a discussion with Their tech guy quita a while ago when they introduced the GAZ adjustable platform rear shock and from memory am sure he mentioned that only one spring would fit it was made shorter 8in to match up with the adjuster on the shock…a standard length spring used on the adjustable platform would give a ride hight thats too high…thats why i sugested contacting them for info…Steve

According to a couple of spring rate calculators on line the stock E Type springs are 250 pounds. I think your choice of this Summit spring is sound. Spring rate is typically a product of the length of the wire used in the active coils and it’s diameter. (Think of a torsion bar that is coiled) One of these calculators lets you compare different steel used in the wire. There is actually not that much difference in rate between the type of steels used. The longer the wire the less it twists for a given deflection which is good - less stress. This length is reflected in the number of coils - the more coils the longer the wire. More coils in a given length however increases the chances of coil bind as they are closer together. I can’t find a reference to how many coils these springs have.
I used American manufactured coil springs in my E Type race car, although not this brand. I found them to be of high quality.

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I had also suggested these guys, who sell 2.5” springs in just about any free length and stiffness your heart desires.

Original specs from Jaguar should be readily available, so I’d start with the closest offering.

These guys are the spring supplier to Gaz, if I’m not mistaken.