Just read the counting coils link you provided - thanks.
On SNG’s site, they have a stock spring with 10 coils but no mention of length. They also offer two 8" springs, 275lb and 325 lb. Both of those have 5 coils (I’m not certain I’m counting the coils correctly). So my 9" coil springs are somewhere in the middle. I’ll take a look at the car but looking at my photo, I think I’ve got 7 or 8 coils.
I guess with the adjustable perches, you don’t want a spring that needs to be compressed. I think you’d want a spring that you can swap easily by just removing the bottom shock bolts.
That’s not true. As someone else already mentioned, your primary interest is the spring stiffness (lbs/in). Aftermarket springs are available in just about every combination of stiffness and free length.
As long as your new spring rate matches the original closely, then the small difference in free length will not be an issue.
Hi Ben, I appreciate your comments but I’m not sure I’m following that. So a 275 lb spring rate has the same ride regardless of spring length? I guess the diameter of the steel in the coil could account for some difference in length.
The car primarily sees spring stiffness, and damper rate from the coil-over. The spring stiffness is linear, so a 275 lb/in spring deflects 1 inch from its free length when you apply 275 lbs, and deflects 2 inches when you apply 550 lbs. That deflection is independent of the spring’s free length.
If you look at the link below, this is (I believe) the spring supplier that Gaz uses. As you can see, you can get a 9” long spring in any stiffness from 150 lb/in to 500 lb/in.
Now, you will likely get better behavior out of a 10” long spring versus a 4” long spring, but seat-of-the-pants, you probably aren’t going to notice the difference between an 8”, 9”, or 10” long spring.
Hi Dave. I wish I could find the web site for a spring rate calculator I used to use. It discussed determining the number of active coils a spring has. The rule with finished springs like the jaguar is to count all coils including the finished ends and subtract 1. Here’s a rate calculator I found that more or less replicated the old site: Compression Spring Rate - Quality Spring, Affordable Prices
I recall that the stock springs are 250 pd springs. The manual is definitive as to the length the springs should be for a stock set up but yours isn’t stock.
My experience with the adjustable dampers that you have (as well as others - I’ve used quite a few) is that the spring perch at it’s lowest setting is higher than a stock spring perch, and if you use a NEW spring of stock dimensions the car will sit a bit higher than stock and can’t be adjusted down. Hence with these shocks you get shorter springs. You should use the site I sent you to calculate the spring rate of the 9" springs you have - how close is it to 250 pounds? If you use significantly harder springs at the rear it can effect handling and you can sense at times the ride is a bit off (not in sympathy with the front). I suspect you can use the springs you have without worry.
I should have commented on this in my earlier post. The spring is always under preload via the shock when installed- probably about an inch or so, or the car will sit way too low. It may be that you will have sufficient room, because the spring is so short, to turn the lower perch down and there by remove the spring ( some of these shocks may allow you to take the perch off from the bottom and let you remove the spring, none I’ve seen allowed it) but I doubt it.
I also have the adjustable Gaz perch shocks. Springs are QA1 and believe 250 lbs rated, 9" long. I am happy with them but as an after thought believe a 10" spring would also work but may have to be compressed to install?
Glenn
Yeah, the slightly shorter spring 10.1 with total of 9.375 coils calculates at 268 pounds and the longer one with 10 total coils calculates at 249 pounds.
Terry,
The springs that I got are listed at 275 lbs. If I ever get this beast back on the road, I should let some of you guys with more experience drive it and let me know what you think.
Dave
275lb springs are only about 2.5% stiffer than stock 3.8 springs, and about 10% stiffer than the stock 4.2, so not a major departure from stock with either.
I run 275 rears on my 4.2 and I find it makes it much more comfortable when encountering dips on a highway at higher speed, compared to the softer original springs. And no discernible impact on ride harshness.