works wonderful on the road. The softness doesn't get any softer. The factory leaf packs had sagged fully onto the overload leaf. That resulted in a buckboard ride. The coil I added there is lifting between 3 and 4 inches as you can see by the airgap on the overload leaf. There is some increased sway on fast turns but nothing I consider an issue. The leaf packs, even though they are tired, are now supporting far less weight( the single coil is probably supporting over 50% by itself) and will last another 18 years.
Anybody that has new after-market leafpacks that seem to be slowly sagging...or carry large amounts of firewood/camping gear....and don't want to replace the leafpacks anytime soon should be thinking about a center coil that is "biased" to give about 1" of lft or so. The leaf packs will likely not sag ever again....and you can dial in the lift.
The dual coil arrangement I have on my DD/worktruck is very soft also but maybe not as soft as the center coil. Even though I have some softer 150# rated coils, I chose to use the 200# versions 'cause I wanted the payload ability. Again, the dual coils are more than just giving casual support to the leafpacks....it's giving a good 3 inches of lift or so and this just fine with this design. No increased sway at all. There is little to no inter-leaf friction because the leafs are supporting almost no weight so the ride is similar to a coiled 'car'...riding soft.
I did not make a retainer/holder for the lower coil mount because it fit so snuggly over the rubber bumpguard. If I was to use this for some offroad, I would then upgrade to a lower capturing plate. The dual coils requires far less fabrication than the center coil....and they are so compact.
I will never remove that center coil on my 87 Runner....it's there for life.