Tires: Tire Size Increase, stock tire size, f350 crew cab

Question
Barry,
I have a '99 F350 crew cab 4x4. The stock tire size was 265/75R16 with a "E" load rating and I've been running 285/75R16 tires with a "D" load rating with the last two sets. I went to buy another set this week and was told they couldn't sell me tires with a "D" load rating for my truck. The heaviest load the truck sees is maybe a skip load of dirt or pulling my 5th wheel. Is there a "real" problem going to the larger tire?
Thanks for the help,
Ron

Answer
Ron,

There are a couple of problems here.

First is the rim width.  The stock rim is a 7" rim and an LT285/75R16 requires a minimum of 7 1/2".

The second is the load capacity.  The LT285/75R16 LR D has 110# lower capacity than an LT265/75R16 LR E.  This means that if someone were to sell you the lower load capacity and something bad were to happen that could be traced to that, then that person would be legally liable.  So most tire shops don't want to put themselves in that position - and I don't blame them.

Further pulling a fifth wheel puts a lot of load on the tire and certainly would require a tire that would be capable of handling it.  Ford has determined that an LT265/75R16 LR E has that capability, and I don't think any tire shop has enough expertise to say that an LT285/75R16 LR D does also - I certainly don't.