Pete, a PO put a set of progressive rate springs in my 87. I noticed them when I was underneath doing an inspection before I bought it so I asked him why he put them in. He was using it to haul a motorcycle and said they helped keep the ride height level with the bike in the back. I've had other Elkys with stock coils and I'd have to say that these progressive rate springs make it little bit stiffer when driving with the bed empty. Ride height is really not affected.