MDMIKE said:
My buddy owns an offroad shop and is considering manufacturing his own coil springs. What are some favorite spring rates for 3'', 5" and 7" coils on cherokees. I read the whole thread on the RE 7.5" coil spring rates and saw what some of you wanted some special rates. He tested a set of stock 6 cyl springs and found about a 125 lb/in. I know people like different rates for different setups so we will assume an added 125 lbs on the front of the cherokee for average bumper winch combos. I dont think a long arm setup would institute a different rate so lets not get into the long vs short arm debate. Any input is appreciated.
I think he should retest, or test some more springs. The FSMs don't cite spring rates, but I've read that stock springs are 180 lbs/inch, Rusty's springs are 160 lbs/inch (and considered "soft" by many people), and that Up Country springs are 220 lbs/inch. 125 sounds VERY soft. Perhaps he had a 4-cyl spring?
I'm not sure I understand your point in mentioning the weight of a bumper/winch combo. That shouldn't affect the rate -- or doesn't have to, anyway. If you know you'll be adding a fixed weight to the front of your vehicle, there are two ways to compensate for it. One is a higher rate spring. But that means a stiffer ride under all conditions. The other is a taller spring.
Use your sample numbers of a 125 lb/in spring, and an added weight of 125 pounds. That extra weight will drop the static ride height 1" but the rate after that will still be 125 lbs/inch. Of course the added weight adds mass, so the ride quality can't be exactly the same, but it'll be in the same ballpark. How do you get back that lost inch of height? If you use a stiffer spring of the same length as the original, you can get the same height but the ride will always be stiffer. Or, you take a spring that's still 125 lbs/inch and wind it a bit more open, so it will settle to the same original height under the added load.
There was a thread a few days ago on which people were throwing around numbers in the 250 lbs/inch range.
I'm almost of the opinion that quality is of more importance than custom rates. I see a lot of threads complaining about a certain brand of coils breaking, and I see a lot of threads about another brand that seems to routinely result in anywhere from 1" to 2" more lift than advertised. I think there's a place in the market for reasonably priced springs that won't break, won't sag within 6 months, and actually provide the amount of lift they advertise.
JMHO
