Custom spring & 5100 adjustable strut combo (1.5-3.5 lift range)

[jjt250]

Hey Matt, I got stock WK CRD springs lying around. I'd be happy to take some measurements if you need any. For what it's worth, there was a noticeable different just by eye when I was comparing Hemi XK springs with my stock WK CRD springs so the OME catalog could be using any WK/XK spring.

[Matt]

That would definitely be helpful man... more info the better!

[paroxysym]

LOL youre crazy matt... but this is educational and ill be staying tuned.

[07JeepXK]

Matt I'm kind of confused. So you said the minimum lift height could be 1.5 inches using the Bilstein struts and the OME MD spings. If the struts at the lowest setting give you 3/4" of lift with OEM springs, how are you getting 1.5 inches as the minimum lift when paired with OME MD spings? Is this due to cutting the springs making them shorter? Because the OME MD springs alone will give you 2 inches of lift.

Ok once you explain that, I need you to help me achieve 1/2 inch more lift then my current OME struts and HD springs by using Bilstein struts and MD springs. Is this possible?

[Matt]

Adam, yes the 1.5" height is due to the cut springs not providing as much lift as un-cut springs (but they'll have a higher spring rate).

Is there a reason you want to use MD springs? The reason I'm using MD springs as my starting point is because the spring rate increases when you cut the spring, and I like the HD spring rate; so I'm basically turning the MD springs into a "shorter" HD spring.

If you want to drop down to the MD spring rate, you could run them un-cut in the 5100s; i'd probably try the middle lift setting and see where that puts you. If it's not high enough once everything settles you can bump them up to the highest setting if needed.

If you like your HD spring rate, and don't have any aspirations to run a modified superlift then you could just get the 5100s and put them on the lowest setting with the HD springs. I believes there's a few WK's running that setup already.

and just to completely derail us....Have you thought about the ICON coilovers?

[07JeepXK]

Well I already have a 4 inch lift in the rear of my XK so I'm half way there. Getting the front components some day could be a possibility. So like you, if it ever were to happen I would probably run a modified Superlift and net about 5 inches of lift. Again I don't know if I'll ever get the front components but if I did it would be nice not to have to go out and buy all new struts and coils once again, I can just do it right the first time.

I do like my HD springs but think if I were to pair them with the Bilsteins at the lowest lift height my cv's and tie rods will be at a greater angle than my liking. I figured since you can gain 3/4" of lift from the Bilsteins at the lowest setting that the MD springs would work nicely. Especially since I could always cut them and bring the spring rate up closer to the spring rate of the HD's and just adjust the struts if more lift is needed once they are cut. I would definitely not want to do any cutting of my current HD springs since the spring rate would go up even more.

I don't think I'd ever spend the money for coilovers on this XK, maybe when I get a Hemi. If I'm spending any great deal of money on the 4.7 it's getting RCV CV Axles.

Why is it that when you cut the springs the spring rate goes up. That's another thing I really never understood

[Matt]

Roger that... so yea you basically want what i'm trying to do. I'll be the guinea pig this go around so hold tight for another month or two and we'll see how it works out

Trying to think of the easiest way to explain how/why the spring rate increases when you cut the spring without getting too technical.
[erased 3 different things I typed...]
In the fewest words possible- there's less material to "deflect". As you remove spring material from a coil spring, which is basically a torsion bar, it requires more force/torque to achieve the same amount of rotation.

Trying to explain this with an intuitive type example...thinking about torsion bars because they're easier to visualize and because coil spring equations are derived from torsion bar equations.... using the image below what does your gut tell you if I ask you this question, "if we shorten the bar a lot, does it get harder or easier to twist it the same amount?". And conversely, if I make that bar really really really long, does it get harder or easier to twist it?



To give an equation type response.... The spring rate (k) of a coil spring is calculated as follows:
k = (some variables) / (some other variables x the number of active coils)

So since the spring rate is inversely proportional to the number of active coils (given the other variables remain constant), as the number of coils decreases, the spring rate increases.

...if that doesn't help, you can come help me install my parts next month and we'll chat it over a few beers and greasy/busted knuckles

[07JeepXK]

That makes sense.

[Matt]

Jacob could you post up more pictures of that spring? Need to estimate the number if effective coils so I can calculate the stock spring rate (assuming material properties similar to OME)

[hoaxci5]

Rears - just so they shown somewhere.
Small Diameter at top and bottom 5 3/4" (14.6cm)
Larger Diameter of center coils 6 3/4" (17.15cm)
Overall length 13" (33cm)
Space between coils 2 1/4" (5.72cm)






All the springs are stock 2007 Hemi Commander with tow package (I think the tow package made a difference in springs somewhere didn't it?)