The Mountain Cat spring is a straight rate spring. The rate may be something like 85lbs. The ZR spring is a progressive rate spring. The rates may be something like 50/95. I'm not too sure about performance characteristics. Some like one, some like the other. I also have progressive rate springs on my ZR but put some longer ones on. The stock springs are too short IMO.
The stock springs were too short, thus the ride height wasn't as high as it should have been. I had to crank the retainer ring right to the end of the threads to get anywhere close to the right ride height; there went my travel. Plus the stock springs were a too soft. The new ones I added were longer and a bit stiffer. So, I had the ride height I wanted and a stiffer front end. I actually had to compress the springs about one quarter inch to get the retainer ring threaded. I know I kept the bag they came in. I could get you the part # if you want.
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