Cutting coils and calculating spring rate

[vagrant]

I have some 8.5"-9" rusty's coils. We have determined (with some help from local racing shop) that the coil rates are actually 262lbs/in. We have stiff Bilstein 7100 12" travel shocks and want to make the XJ drive like a Jeep Speeder (good handling and responsive steering, but plenty of wheel travel and stiff).

I want to cut the damn things though because they are just too tall. I can also revalve the shocks easily as a neighbor does his own revalving and has the same shocks I do. We will run the adjustable JKS spacers with the air bumps on the front to dial it in and set corner weights.

So I guess my question is what is the best way to cut coils and how will I determine lift height and spring rate without taking it back to the racing shop for measurement (it's 84 miles from me, so it's a far piece).

 

[Goatman]

You can cut the coil with a cutoff wheel. You can figure the lift height by putting them on a measuring after you cut some off.


I'm not familiar with Rusty's coils, so don't have any personal knowledge. The Currie/Deaver Jeepspeed coils are 250/300, for sake of comparison. If those coils are actually 262 lb/in, that's already decently stiff for an XJ coil. Sway-A-Way has a spring rate calculator: http://www.swayaway.com/calculators/swayawayCalc.php#step9

Estimating lift height difference is pure trial and error. If you know you're exact corner weight maybe you can figure out how to do the calculations, but even then it's an estimate. I'd figure that since you're slightly increassing the spring rate as you shorten the coil, you're lift height change will be slightly less than the amount you cut off. Cut off 1" and you'll like loose .9-.95" of height. Springs are cheap, and you won't know if you'll like the ride and handling until after you do it anyway, so just start cutting.

BTW, I run 8" Skyjacker coils with one full coil removed. It's great for the fast stuff, but now it's a little rougher on the trails. For hardcore crawling it's good, I don't notice it, but for the bumpy/rocky trails in the mountains it's not as cushy as it was before.

 

[vagrant]

Thanks, Goatman! You're reply helps greatly and I appreciate it.

I'm going to cut a coil off like you've done. It really shouldn't be that much of issue with the ACOS installed as I can just even it out using those if I get a little "off" with the cut.