I know the stock size is 225/45/18 for the SS tires.

But has anyone tried a different tire size and had success?

 

yes, different tires have different tread patch widths, on the same size (supposed) tire. I tried a few, 245x40 is probably the most popular. The 255 x40 i am running now would probably work on the 7.5 but it has a narrower foot print. It has been hit and miss, Pick some you like and mount one.