I need to replace the tires on my truck. I have what I acknowledge is a stupid question to anyone with more familiarity with this issue than I have -- which is likely everyone. Current tire size is 285/70-17. Tires in this range can be awfully expensive. Which of those parameters can I change in a new tire purchase? Any of them? Obviously the rim diameter (17, right?) isn't changing without the wheel changing and I'm not changing the wheels. I THINK I understand that 285 is tire width in mm. But is that the width at the rim (in which case I assume I cannot buy a different size) or the width measured somewhere else (in which case I assume I could use a different width)? As for the the 70 -- I do not have any idea what that number means. ETA: Maybe a simpler question: Can I replace the current 285/70-17 tire with a 265/70-18 tire on the existing wheel? (I get it -- if you understand this stuff it sounds like asking if i can shoot .45ACP out of my 9mm. But I'm ignorant in this topic, so. . . _ Thanks in advance to the GT braintrust.