Tires hurting my gas mileage?

06JeepLiberty · **Posted:** Mon Apr 07, 2008 8:06 pm

I'm new to the site and was curious about my tires.....I got it about a year ago and the previous owners apparently put tires on it just before they got rid of it. They're Cooper Discoverer S/T 245/75/16 on the stock wheels. It does rub a little, but only when making a U-turn, or sharp turns. I'm just curious as to if the larger tires effect gas mileage. I've been told yes, and no..so I'm not sure what to think.
Also, they didn't get a 5th one..so my spare is stock size 225/70/16. I'm thinking it'd be a good idea to get a 245/75/16 for my spare in case I get a flat, right? (I'm looking at BFG All Terrains..nice tires)
Any help is appreciated..sorry for all the questions. Thanks guys & gals!

Guest · **Posted:** Mon Apr 07, 2008 8:08 pm

245/75s are creating the illusion that you've lost gas mileage. Since I put my 245/75-16 MTR's on, replacing my 235/70-16 Discoverer ST's, my calculated MPG has dropped about 2.5-3mpg, but I haven't been spending any more money on gas.

Get your speedo recalibrated, and I'm pretty darn sure you're gonna magically get back almost all the gas mileage you "lost"

Jeep Dawg · **Posted:** Mon Apr 07, 2008 8:45 pm

The BFG's are nice. I love them and use them on every jeep I ever had. Currently I have BFG AT/KO 225/75/16 and my gas milage has droped because it is a heavy tire.

Pote · **Posted:** Tue Apr 08, 2008 9:31 am

yes you are losing some mpg. like above, though, your speedo and odometer are now pretty far off. so its not as bad of mpg as you think. My speedo is off by 1 mph at 60 mph and my odometer is off one tenth of a mile ( I have 245/70/16s). so for every 100 miles I drive showing on the odometer, I have really driven 110 miles. Your will be even more drastic because your tires are yet another couple sizes larger.

Just from the physical standpoint, you may be losing mpg with a higher rolling resistence on larger tires as well as a much higher weight per tire. just those two things will decrease mileage. So the answer is really yes and kinda no. LOL

Jeepman56 · **Posted:** Tue Apr 08, 2008 9:46 am

Like Pote said, more rolling resistance is added plus weight, but the reason your speedometer and odometer are off is because your tires are bigger. This also means you are getting more travel per rotation which serves to counteract some/most of the added weight.

VTNomad · **Posted:** Tue Apr 08, 2008 4:08 pm

You're speedometer and therfore your odometer will be off with larger than stock size tires. This could account for a difference in your calculated MPG's.

06JeepLiberty · **Posted:** Tue Apr 08, 2008 7:44 pm

Alright, thanks to those of you who responded. I got what I needed to know!

KY Liberty · **Joined:** Sat Jul 09, 2005 1:46 pm **Posts:** 1195

Bigger, heavier tires can lower your gas milage. I got my speedometer corrected, and still appear to have dropped about 2 mpg going from 245/65R17 Destination AT's on 2005 17X7.5's to 245/75R16 Wrangler Silent Armors on 16X8 Rubicon Moabs.

DryBones · **Posted:** Tue Apr 08, 2008 7:54 pm

KY Liberty wrote:

Bigger, heavier tires can lower your gas milage. I got my speedometer corrected, and still appear to have dropped about 2 mpg going from 245/65R17 Destination AT's on 2005 17X7.5's to 245/75R16 Wrangler Silent Armors on 16X8 Rubicon Moabs.

when I got my Fuzion's mounted I asked the tire guy about the Silent Armors and he said he hates them because they are soooo dang heavy and hard to mount :lol:

KY Liberty · **Joined:** Sat Jul 09, 2005 1:46 pm **Posts:** 1195

I absolutely love the SA's, other than the gas milage. It's hard to believe you're riding in the same Jeep you just climbed into. They're very smooth and quiet for an aggressive looking tire. The snow and ice traction this winter was amazing too. Didn't have any trouble with mounting or balancing, but I also got them balanced with the little beads. Very noticeable mpg drop though.

Pote · **Posted:** Wed Apr 09, 2008 12:36 pm

DryBones wrote:

KY Liberty wrote:

Bigger, heavier tires can lower your gas milage. I got my speedometer corrected, and still appear to have dropped about 2 mpg going from 245/65R17 Destination AT's on 2005 17X7.5's to 245/75R16 Wrangler Silent Armors on 16X8 Rubicon Moabs.

when I got my Fuzion's mounted I asked the tire guy about the Silent Armors and he said he hates them because they are soooo dang heavy and hard to mount :lol:

One of the biggest gripes by tire guys about General Grabber AT2s. Those things are uber heavy!!! same with KOs. Like driving around with a whole other passenger in your car...I think they run about 125 lbs more than my AT tires (counting all 5)....easily about 200-250 lbs more than what comes from the factory...that's a lot of extra umph.

Christopher · **Posted:** Wed Apr 09, 2008 12:56 pm

Just remember spinning mass will effect your mpg much more than just adding wieght like skids and bumpers.

Chris

tjkoen01 · **Posted:** Thu Apr 10, 2008 10:32 am

ThunderbirdJunkie wrote:

245/75s are creating the illusion that you've lost gas mileage. Since I put my 245/75-16 MTR's on, replacing my 235/70-16 Discoverer ST's, my calculated MPG has dropped about 2.5-3mpg, but I haven't been spending any more money on gas.

where are you getting your gas?! you must be the only one not spending more! :lol:

Guest · **Posted:** Thu Apr 10, 2008 8:36 pm

Usually from Chipotle, but sometimes Gold Star Chili can tear me up too.

InCommando · **Posted:** Thu Apr 10, 2008 10:24 pm

LOL.

My 285/75/r16's on soft 8's weigh almost 120# each corner.....

tjkj2002 · **Posted:** Thu Apr 10, 2008 10:35 pm

InCommando wrote:

:shock:

LOL.

My 285/75/r16's on soft 8's weigh almost 120# each corner.....

My 265/75 Trxus MT's(load range "D") on 16x7 steel wheels is 92lbs each,my 35x13.50 Toyo's on 15x8 steelies are about 115-120lbs each(load range "C",thank god).My stock 16x7 alloy rims and SR-A's was 48lbs each(got rid of those at mile 3),and my stock alloy's and 245/75 MT/R's(load range "E") was about 75lbs each,then my stock alloy's and 225/75 MT/R's(load range "D") was about 65lbs each,then 265/75 MT/R's(load range "D") on 16x8 "simulated beadlock" steel rims was 105lbs each.

For every one pound of spinning weight(tires,wheels,rotors) is like adding 10+lbs of static weight to your KJ,not to mention wider tires cause more wind resistance and friction between it and the road surface.Bigger,heavier tires also severly effect the stock brakes.

tjkoen01 · **Posted:** Sun Apr 13, 2008 5:30 pm

ThunderbirdJunkie wrote:

Usually from Chipotle, but sometimes Gold Star Chili can tear me up too.

that's why i stick to the tacos, 3-ways and coneys (no beans)!

InCommando · **Posted:** Sun Apr 13, 2008 8:58 pm

tjkj2002 wrote:

InCommando wrote:

:shock:

LOL.

My 285/75/r16's on soft 8's weigh almost 120# each corner.....

My 265/75 Trxus MT's(load range "D") on 16x7 steel wheels is 92lbs each,my 35x13.50 Toyo's on 15x8 steelies are about 115-120lbs each(load range "C",thank god).My stock 16x7 alloy rims and SR-A's was 48lbs each(got rid of those at mile 3),and my stock alloy's and 245/75 MT/R's(load range "E") was about 75lbs each,then my stock alloy's and 225/75 MT/R's(load range "D") was about 65lbs each,then 265/75 MT/R's(load range "D") on 16x8 "simulated beadlock" steel rims was 105lbs each.

For every one pound of spinning weight(tires,wheels,rotors) is like adding 10+lbs of static weight to your KJ,not to mention wider tires cause more wind resistance and friction between it and the road surface.Bigger,heavier tires also severly effect the stock brakes.

Mine are "e" range on 16x8's & thankfully they are on the Cherokee. I honestly don't know what that kind of weight would do to the D30a.

Tires hurting my gas mileage?

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