I've been running sumo springs on my Jeep JKU for several years...my Jeep is heavy and the Sumo's have been a god send. As a poor man's air/hydraulic speed bumps, they soften the hard jarring/g-outs while traveling at speed. While crawling/low speed use, I find the additional spring rate to be a little too high. However, the trade-off for higher speed performance is well worth it.
When I've loaded it a lil heavy (using it as a hauler for my home reno or for the beginning of a lengthy trip), the sumosprings do a nice job of assisting the main springs from time to time. It is obvious when they kick in/are engaged.
I would NOT want to ride on them full time - few if any of the installations I've seen (or on my ride) permit sufficient suspension travel for overland use. The ride is too jarring and I'd be worried about bending an axle, flange or worse...
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