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Old 10-20-2013, 03:58 PM   #1
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Tire selection and sizing help

Hello,

I am looking for upgrade the tires on my van. The van came equipped with 17x8.5 wheels and 285/70/17 Hankook Dynapro atm tires. Front tires are fine, but the rears a getting a little low; I could just buy two new rears, but I'd like t upgrade to "E" rated tires and the Dynapro is a "D" rated tire.

I've read a many postings here and based on my research, the BFG All Terrain T/A KO appears the best choice -- like many 4x4 owners, I drive the highway 90% getting to my off road destination, so I want something decent on the highway. Off road usage is modest, I am not into hardcore wheelin', just want to get through mud, snow, sand when necessary. Are there other tires I should consider?

Then to the topic of size: in "E" load rated BFG offers the T/A in two sizes that fit my wheels: 285/70/17 and 305/65/17. I would be inclined to choose the wider tire due to increased foot print, but wonder about the lower profile sidewall at "only" 65. Thoughts on this? I've also looked into 33's or 35's but I am new to truck tires and I am not clear what would fit my wheels.

Appreciate the help.

DJM
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Old 10-20-2013, 06:31 PM   #2
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Re: Tire selection and sizing help

Quote:
Originally Posted by djm68
I would be inclined to choose the wider tire due to increased foot print, but wonder about the lower profile sidewall at "only" 65.
I have been going through the same considerations as you and I came to a realization through doing the math that may help you. As I understand tire sizes, the first number represents the width of the tire in millimeters. The second number is the ratio of sidewall height to tire width. The third number is wheel diameter. Here is the math to determine the height of the sidewall in inches between these two sizes (25.4 is millimeters per inch):

285 x .70 = 199.5 / 25.4 = 7.854 inches
305 x .65 = 198.25 / 25.4 = 7.805 inches

So if my calculations are correct, the difference between the sidewalls is 0.049 inches smaller on the 305. I wouldn't think that could be called a "lower" profile. Hope this helps.

Steve in L.A.
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Old 10-20-2013, 07:18 PM   #3
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Re: Tire selection and sizing help

There are bazillions of tire size calculators online with pictures and whatnot; google away.

I got this:

Specification Sidewall Radius Diameter Circumference Revs/Mile Difference
285/70-17 7.9in 16.4in 32.7in 102.8in 617 0.0%
305/65-17 7.8in 16.3in 32.6in 102.4in 618 -0.3%

Meaning you actually lose a bit of width. But they're so close as to be insignificant unless you're running NASCAR or something. The BFG's are a popular tire; I love 'em. But YMMV. And I'm not a fan of E tires, but we've beat that to death. There have been a lot of threads on this so look at some older posts; not much has changed in the last few years.
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Old 10-21-2013, 10:11 PM   #4
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Re: Tire selection and sizing help

Thanks for the input, guys. As you've both pointed out, there is really not much difference between the 285 and the 305 tires - the price difference between the two is more than the actual size differences.

This link provides a nice graphic showing the difference between 285 and 305 sizes:

http://www.tire-size-calculator.info...ww=8.5&2off=40


Thanks,
DJM
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Old 10-21-2013, 11:53 PM   #5
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Re: Tire selection and sizing help

I attempted to be honest with the number of hours I spend on highways vs. off-road and am running BFG Rugged Terrain T/A in 275/70R18. I have yet to run into anything close to a traction issue on dirt. On road they are no fun where big rigs with chains have worn ruts over donner pass on i80. No issues otherwise.
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