Hey mate,
I'm currently trying to decide on some coils for my gq ute. I have been favouring the dobinsons for a heavy duty spring. Even though the rep I spoke to at the show was a total douche I think they still have a great product.
From what I have found out (this hadn't been from personal experience, just reasearch so happy to hear differing opinions
) that a progressive coil will just sag if they are loaded as they generally not designed for heavy duty applications.
It sounds like you have a heavy rig, if its always loaded I would get your car on a weigh bridge and find out your total weight then weight over front and rear axles and talk to who ever you are going to get your springs from as to what rate to go for and leave out the air bags.
I'm pretty sure most spring manufactures will make custom springs if their standard range isn't heavy enough as they tend to only make them heavy enough to take a vehicle at its GVM which I'm tipping you are well over.
Previously my ute weighed 3.75t fully loaded with 2 passengers, that's 850kg over gvm!
Oh and if you haven't sorted your spring hats I would be doing that first, there are a few options now as its a common problem.
Cheers benny
