Assuming your chart is correct, in this particular example, the Currie 4" spring will limit travel before the 4.5" MC does. But in reality, once you get a shock with more travel and a longer compressed length, it will likely be the shock limiting up travel. The reason people say generalized statements like:..."MC springs limit up travel vs other springs" is because the rear MC springs bind up sooner than the Currie.
Yes that does make sense, thank you. The part that confuses me is when people say they limit up travel, but the listed height when they go solid isn’t really any different than comparable coil springs (my examples of the chart posted above).
That also explains it. You seem to understand it with the same viewpoint as I do. Thanks.
There are no progressive springs on the market. Rockjock, savvy, Currie, Rancho... doesn't matter they are all going to follow physics the same. Companies can vary spring rate by changing the pitch, or the distance between the coils. And while it's true for every pitch change, there is a spring rate change, when the spring is compressed they all average out to a single linear rate. Research dual and triple spring coil-overs if you want to understand more. Doesn't matter if there are two, three, or four pitch changes. The only time a spring can actually change rates is when one coil collapses onto another coil, then both of the touching coils are removed from consideration. Then, and only then, the remaining coils determine the overall spring rate.
This is definitely not good. These were the 3.5 inch Metalcloak coils? 4 cyl or 6 cyl? How long until they sagged?
After looking at the chart for the rear more closely, I see how the Metalcloak rear coils could limit up travel sooner vs others. I missed that before I guess.
Yes 3.5" coils with a 6cyl. Had 4.25 for about 2.5 years, until I added the weight. After 4 months, I was down to 3" front and 3.5 with just my 35 on back. Factory rear bumper. I had sandbags in it for a while, to help the ride. I also loaded it up with supplies a few times. I wouldn't have expected it to sag like that. Even after removing the bumper at 4 months, it only went up to 3.25". I added the factory bumper, and an aluminum winch plate, and it stayed at 3.25. I too was hoping to keep around 4" when I got them. Just put 1" spacers on it today.
Your first paragraph makes a lot of sense. So, it’s true that a coil spring can have variable spring rates due to pitch or distance between the coils. If so then the RockJock/Currie 4” have a variable spring rate, right? The coils are closer at the top than the bottom. I think the average rate is of those coils is around 115in/lb based on weight added/taken away and measuring the coil. Average rate is the rate only until the upper coils collapse, then the rate is only the lower rate. Is that all correct?
The Rockjock variable rate spring will behave exactly as any other spring until the coils start stacking up. As each winding lays down on the one below it, it becomes a dead coil, and the overall spring rate will increase. Take a coil thats 10" long with a rate of 100in/lb. Then manufacture the same coil but twice as long. This new coil will be 20" long, but have a rate of 50in/lb. As a coil get shorter its capacity to hold weight increases. By having a variable pitch the manufacturer has the capacity to tune when the spring has more capacity to support additional weight.
They are progressively wound, they do not have a progressive rate. The rate is almost 100% linear. The factory is the only supplier of actual progressive rate springs and then only on the rear of the TJ. If you take a pair of calipers to one you will quickly note that they used a single piece of wire, tapered both ends for several turns to a fat middle section. The only way you can build an actual progressive rate spring.
Interesting. I pulled the chart info from the resources thread here on the forum. Was this 1 inch difference true for you front and rear?
I was dealing with it specifically in the rear, since i went to coilovers up front.
Thanks for the reply. I was actually hoping to get a little more lift than that out of them. My Jeep may be lighter than yours just by looking at your profile. You switched to Savvy 3 inch coils? How much lift did those get you and your thoughts on them?
The Savvy 3" coils got me about 2.75" of lift in the front, and I ended up adding a 10mm trim spacer. The Rear springs netted me right around 3.25-3.5" of lift,
I have some MC 4" springs for sale.
