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Tire sizing

39439 Views 49 Replies 36 Participants Last post by  Slammer67
As a new member, I've noticed that a quick tutorial about tires might help in answering some questions. Not necessarily about what size will fit what year, but some basic info that could help answer questions before you ask. Basically what the numbers mean, and more important, making sure that AWD owners get what they need. It has been pointed out that AWD owners already know that different size tires don't do well, but do they know why, or know when they are being led astray by a tire dealer?

The sizing is a 3 part "sentence". The last part of the tire size is the easiest. It's the size of the rim. I believe our vehicles(stock) take 15". The first part is the width, in millimeters. Here's the tricky part. The middle part is a percentage of the first part, and represents tire height. So this means that the height of a 235/70/15 is different from a 245/70/15. Height has everything to do with circumference, and that has a dramatic affect on AWD vehicles.

How I learned this lesson: I bought a set of 4 tires. They sold me(on the receipt) 70 series size tires, but the tire they installed was 75 series. Not a problem in itself, but 2 years later, when I went to another branch of the same company to get 2 of them replaced, I flashed the original receipt and they sold me the 70 series. The difference between 70s on the front, and 75s on the rear ate up my transfer case in about 3 weeks. It was my transmission guy that figured out why, and that info forced the tire company to pay for the transfer case repair, about $800.00, about 7 or 8 years ago.

This experience has taught me that I should never trust that I actually get what I bought.
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aperine said:
I need to trim my wheel wells to accommodate 30.6" (265/70-R16) tires on my 2003 AWD Astro. I am using a 2" body lift plus torsion bar crank (front) and add-a-leaf (back). The instructions provided by Journeys Off Road are good, but not quite detailed enough for trimming of the rear side of the front fender. I am hoping someone has video footage of this operation before I cut into my mint '03...please.

I have basically the same lift with the same size tire 255/75r17, but about the same diameter. For the rear of the front tires I basically just laid the pinch seam over to clear.

Not the best angle, sorry.

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