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Tire sizing

39409 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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I plan to run a 245/70r16 tire on my Astro. Stated tire casing width is 9.75 (tred width 7.6). Has anybody it a 245/70R16 on the Astro. Seems that the inside tire casing will get awfully close to the rh front sway bar when front wheels are cranked.
Any input?
Does anyone have experience as to the various tire Load ratings when selecting a larger off- road tires for our lifted Vans? Given our Vans have a GVWR of 6100 lbs, and the stock tires were 215/75/15, alot of the larger tire choices are either LT or SUV rated. 6100/4 = 1525# per tire stock. I am looking to go to a 235/70R16 or 245/70R16 tire size and wonder about ride quality. The LT tires are 10 ply and rated up to 2460# load, whereas the P series SUV are rated to more like 2065#, still well above the stock load ratings. I guess want the ride quality of a 6 ply P rated tire, but do no want to sacrifice sidewall flex in cornering. Seems to me with the wider tire footprint and higher load rating, that an SUV tire should be fine? Any thoughs ?
How about running 17" rims and a 235/70r17 tire p metric? Since the sidewall is shorter, perhaps it will corner as weel as a LT tire (less sidewall squirm) without the harsh ride?
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