Tires...how much can you safely (if at all) deviate from manufacturer's stated sizes?

Question

For instance, my truck calls for "265/70-16" and I find "245/70-16". I've tried asking both tire shops and mechanics and get conflicting answers.

Answer 1

you have some lee-way (sp?), those tire sizes arent too far fro each other, the best thing to do is measure from he bottom of the tire to teh top, fully inflated and mounting on a rim, you can normally, go up an inch or down an inch with out effecting too much, it will not effect your steering geometry, however, tires that are not the same size as the factory tires will throw off thespeedomoter, if they are smaller, you will be going faster than the speedo reads, and larger tires you will be going slower, not by much, but it does effect it, also it will effect your gas mileage.

Answer 2

You would want to stay with the same size but there is not much difference here and you will be fine if you run the 245's.

Answer 3

I had the same question.  I went to my local Discount Tire shop and the the technician was able to look it up on their system.

Answer 4

Logic tells me as long as the tire you choose falls within the weight range for your truck it doesn't matter what kind you use. Each tire is labled how much weight it can carry at a given air pressure.

Answer 5

You don't want to deviate very much at all,  the tire sizes were determined by engineers familiar with the characteristics of the vehicle and tires involved.  

You need to understand what the numbers mean.   The first (265) is the width of the tire in millimeters.   The second (70) is the height of the tire in a ratio to the first number.   In your question,  the second tire will not only put less rubber on the road  (the footprint),  but have to turn slightly faster to go the same speed as the first because it is about 14mm diameter smaller.      The last number is the diameter of the wheel the tire will fit in inches.   There is no variance on this number.

By the same token,  switching tire sizes greatly will affect the way it fits on the wheel.   A tire intended to fit  a 6 inch wide wheel will not sit flat on the ground on a ten inch wheel,  but require pressure changes to even it out,  bowing the sidewalls out of spec and damaging the tire.