Xtreme RC Cars Magazine did a great article about a year ago where they used a spring dyno and tested all the major manufacturers springs. The spring rates that are published are usually off by quite a bit. So you could be looking at company X's 17# spring and company Y's 15# spring and they one that's rated at 17# could actually be lighter than the other companies 15#. I think it was in May or June of last year when that article cam out. It's proved very useful.