My 2005 Roadster has 6 leaves and therefore a hard ride. I suspect this changed as Colin suggests - soon after to 4 leaves with bigger diameter U bolts. (Exact dimensions escape me without checking). May have been 3/8" to 7/16".
Interestingly my 2012 Plus 4 had poor rear springs which bottomed constantly. Replaced last year with 4 seater springs has transformed it.
