[asphaltgambler]

There's a lot more to the equation here. Spring rate is determined by load (lbs) to deflect the spring 1". Load rate is the maximum weight a spring will safely carry at a manufacturer's stated compressed height. So, if you have the preload set at full up, does the vehicle sit and drive right? I'm not talking about tire rubbing. Depending on coil / shock length / mid-point travel you may or may not have an adequate spring rate.

If this is a custom deal, you should corner weigh the vehicle, measure spring compression at ride height, then figure out if the spring is matched to your application. Tire rubbing could be too much lateral movement or an improperly set panhard bar angle ( if you have that). But from your OP, not near enough information to provide the correct answer other than what I've already provided.