Tires: 2 or 4 replacment tires, rubber manufacturers association, f350 diesel

Question
I recently had a some one drive into my rim splitting my rim and tire-can't believe he didn't damage my box. i have a 2006 F350 diesel 4x4. the dealership which is repairing my vehicle recommends 4 new tires as i have 40% wear on my front tires. the insurance company wants to only replace the 2 rear tires. fountain tire told me that they will not replace only 2 tires on a 4x4 if wear is over 3/32, they will only replace all 4 tires. I talked to the rep at the ford dealership again and he said he has customers actually sign off on the danger of only repalceing 2 tires if the old ones are 3/32 or more difference from the new tires? what is the correct recomendation and how firm should i be with the insurance company about have ALL 4 tires replaced instead of only 2- i was the victim in this case... why should i have to pay for any of the tires? is there a written recomendation from ford ort fountain tire or anyone?

Answer
Wayne,

The standard answer is that on 4X4's, you need to have 4 identical tires - smae size, same make, same model, and same state of wear.  That's to prevent the drivetrain from binding up and damaging the components.

Here's something from the RMA (Rubber Manufacturers Association):

http://www.rma.org/publications/tire_service_professionals/index.cfm?Publication

What you want is in Chapter 3:  Tire Replacement Guidelines.

On page 42 there is a note in a blue box:

In some cases, the vehicle manufacturer may
specifically advise against replacing less than all
four tires. Always check and follow the
recommendations in the vehicle owner’s
manual. For 4WD and AWD vehicles, even small
differences in outside diameter may cause drivetrain
damage or mechanical malfunction.


So unless Ford specifically says it is OK to replace only 2 tires at a time, the advice to replace 4 would apply.  Since you are in this situation because of an accident, the insurance company is obligated to "make you whole" - that is put you back to where you were before the accident.  Since they can't put you back into 40% worn tires, a compromise is them paying for 2 tires, and you paying for 2 tires seems reasonable.  With that, you would have 4 tires that are going to go further than before the accident.