Upgrade Tire from Stock. Any effect on MPG?

[NavyVet1959]

My JL Sport came with 245/75r17 tires and I'm looking to upgrade to a 285/70r17 set since I read on this forum that its the max size I can go on tires without getting a lift.

My question is, how bad will my MPG be affected because of the tire size change??

Any MPG differences between a A/T and M/T?? I love the aggressive look of Mud Terrain tires but I'm afraid of the MPG loss.

Also any advice on how Mud tires will affect my daily driving? The All terrains look much less aggressive than mud tires do.

Any advice would be appreciated.

Thanks!

The 285/70R17 will be a 32.7" tire. I was able to put LT275/65R20 tires from a Ram 1500 on my JL (with a 1.25" wheel adapter), but it would rub against the "euro guard" fairing that go between the bumper and fender. I removed the euro guard fairings and it did not rub. Looks better without those things anyway. The LT275/65R20 is normally a 34.075" tire, but these have quite a few miles on them, so they might be closer to 275/60R20 in size.

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[cwmartin59]

I found this info several years ago. I use the following information to help figure out what tire size I might want to upgrade to:

To help understand tire sizes a little better here's a quick lesson.
For an example we'll use a fairly common tire size for trucks with a 3" lift, a 285/70/R17.

We'll first label the parts as follows:
285/70/R17
_^__^__^
_A__B___C

A- This is the width of the tire in millimeters. The conversion is 1"= 25.4mm so for our example: 285/25.4= 11.22" width.

B- This part is the "aspect ratio" of the tire and is a relation of the tire's width to the sidewall height of the tire. In our example it's '70'. This means the sidewall height is 70% (.70 in calculation) of the width of the tire. That means the sidewall height is:

11.22 x .70= 7.85"
BUT there is a 'sidewall' both above and below your wheel when measuring height, so you must multiply this by 2 when calculating the tire's overall height.

C- This third piece is simply your rim size. So, for a final calculation of a tire's size, you add this to the total from part B.

In conclusion, a 285/70/R17 equates to 11.22" wide and is (7.85x2)+17"= 32.71" tall, or basically equivalent to a 33x11.50R17 if we called it a standard size.

How about one more example, 265/75/R16:

Width: 265/25.4= 10.43"
Sidewall: 10.43 x .75= 7.82"
overall height: (7.82" x 2)+ 16"= 31.64" tall. Basically, a 32x10.50R16

This method of finding a tire size will work for every metric tire size out there!

NOTE:
It should also be mentioned that different manufacturers' tire sizes will slightly vary from these calculations. Its usually a very minor amount but it's still there none the less. For this reason I recommend everyone looking at tires to go to the respective Manufacturers web site and look up the exact specifications they list for the tire before buying a set, or to compare tires between different manufacturers.

Hope this helps someone and that you can calculate tire sizes without having to be reliant on a program.