Tires: load capacity...is E a must?, passenger car tires, discount tire store

Question
I have a 96 2500 Suburban that we use for towing a toy hauler about 8-10 times a year. Other than that it will be used for some winter driving (Salt Lake City) and the occasional trip to Home Depot.

I've been looking for tires for 2 months now and couldn't decide between buying some 265/75/16 to replace the 245/75/16 on factory rims (rims are 16x6 chrome rims from a 2005 GMC) or just buying rims and tires for a good look. Well today I found a killer deal on new in the box 20" rims for $65/wheel. http://www.discounttire.com/product/...mraz.mm.xl.jpg
They are from a Discount Tire store that had these in their inventory and they just wanted to get them out of the store (normally priced $150).

Now for the question:
Am I going to be alright putting a Nitto Terra Grappler 305/50/20 tire on there? I know the size should be fine. I'm worried about the load rating. Technically it is not an LT tire. However, Nitto specs it as being an extra load capacity tire with a 121 load capacity (3086 lb/tire @50psi). The weight capacity seems good, but is a 4ply tire going to be alright?  Currently the truck has 245/75/16 BFG with a 120/116s load rating (3042 lb). So doesn't that imply that the Nitto 305's would be able to handle the weight just as good with the 3082 lb?

Thank you,
John Cluff

Answer
John,

First let's get some more facts.

On every vehicle sold in the US, there is a sticker – commonly called the tire placard - that lists the original tire size and the proper pressure for that size.  The placard is usually located on a doorpost or in the glove box – but sometimes it is located in the trunk or on the fuel filler door.

So what does your placard say?  If it syas LT245/75R16's, then you need to use an LT tire - and the Nitto doesn't qualify - not enough load carrying capacity.  

There is a quirk in the way load carrying capacities are done.  Passenger Car tires used in a light truck, (such as a pickup or SUV, or in trailer service, have to have their load carrying capacities reduced by 10%.  That means in order to get the same effective load carrying capacity as the BFG's you would need a Load Index of 123 for a passenger car type tire.  They do not make some PC tires with that high a Load Index.

I can not in good faith recommend doing what you are considering, and I suggest you stick with LT tires.