Dave, you're on the right track, but the key is this:
valhalla360 wrote:
You may need to change tire size to get the higher ratings...
You are correct that the RAWR on SRW trucks is mostly the product of twice the rear tire rating.
However, not all E rated tires are rated the same...I happened to be looking at Nitto Ridge Grapplers so we can use that as an example. Look
HERE at the load rating table for 17" tires. The highest load-rated tire is the LT285/75-17E at 3195 lbs.
Now look
HERE at the ratings for 18" tires...that same tire in LT 285/75-18E is rated at 4080 lbs.
In this example going from 17" to 18" with the same 285/75-E tires nets up an increase of 1,770 in RAWR just from the tires.
Make sense?