I need some help to answer a friend's question. I'm more familiar with older fords, so I want to ask here to try to get the right answer for him.
His wife cut one tire on his 2008 Expedition. He replaced two tires rather than just the cut one. He was able to find the same make and model tire as he had on the vehicle. His other two tires are approximately 50% worn down.
Someone told him that he has to replace all 4 tires so they are all the exact same diameter or he will harm the 4x4 system.
I realize the newer vehicles monitor tire rotations for traction control, braking, etc.
Is this correct, that he should get all 4 tires or would it be within acceptable tollerance to run 2 old and 2 new tires with the same make and model?
No, this is not correct. Unless the tires are near bald, you don't need to. Should all 4 tires have the same tread wear? Well in a perfect world when money is no object. She would have been fine with buying one tire, as I did. It won't harm anything.
In all reality you should replace two (keep two new on the same axle) as you can throw the vehicle out of balance. You should actually look to make sure all 4 tires you put on a vehicle come from the same mold w/ the same date code. Take it from someone in the fleet business, replace all tires on the same axle.