I have an 02 Ram 2500 Quad 4x4 and it has 265 75R 16 in tires on it, I was given a real good set of 245 75R 16 in tires and figured I might put them on for the winter. There is about an inch difference in the overall diameter of the two and was wondering if that would effect ABS or something like that? It calls for either at factory level in other words it could have came with either size. Would the speedo have to be changed?

 

Your speedo will be off about 3%. Dealer can adjust computer for the difference. You should not have any problems running that size. Mine came with 245's and I've been running 265's since the factory tires wore out. 245's look really small on these trucks.

 

Your speedo will say you are going faster than you are with a smaller diameter tire, but 3% isn't much. I wouldn't worry about that.
Your mileage will drop a little since they will need to turn more to go the same distance, but that will also be negligible.

 

My '02 ran great on the 245's, my '99 is running 265's and is 4 mph off at 55, really doing 59 according to my GPS. The power is much better with the 245's, the mpg's are better with the 265's but only on the open highway.