They are almost the same in real terms...if anything the 60 profile is smaller in real terms hence the smaller rolling diameter.
Besides that a 96 load rated tyre has no business anywhere near a vehicle of your weight. I'd imagine it'd need to be more like a 103 load rating. Something like a 235/55R17 Continental VancoContact or GT Radial Champiro HPX - both have load ratings of 103 and a W speed rating.
If your current tyres have anything less than a 103 load rating then.....there's your problem.