I am planning on getting new tire for my Blazer and have found the brand and model I want, however I have several choices within my size and want to make sure I get the right one. My question is this: should I get the tire with the higher or lower revolutions per mile? One tire is rated at 720 and the other is 670 - quite a difference for the same size tire (235/75r15) but I can account for the difference in tread depth, even though they are labeled the same size. I have been trying to figure it out in my head but I'm not sure that I am getting it right. I think I want the lower rev tire (670) - right?