Bad MPG after new tire install...?

I just got rid of the little stock Dunlop's (245's) for a set of Firestone Destination AT's (265/75-16's). I can't believe how horrible my mileage has gotten with the bigger tire. I thought i'd sacrafice maybe 2-3 MPG. I used to get about 25MPG with as high as 27 on long drives. I drove about 500 miles the other day and at one point got as low as 16. Looks like i'm averaging about 18-19 now and that's over about 2,000 miles since the swap.

I've heard about cruddy winter gas that reduces your efficiency and the tire swap happened right at start of winter. Any truth to this?

Thanks

 

You've got a few things working against you. Winter blend fuels do suck. According to the EPA, summer blend gas has 1.7% more energy than winter blend gas.

The increased weight/rolling resistance of the new tires might have the biggest affect on the mpg in your case. The Destination A/T's weigh 43 lbs vs the Dunlops at 34 lbs.

The odometer and speedo will also be slightly off with the new tires. To calculate your mpg you have to multiply by the % change from the old tire size to the new tire size. Using the tire calculator it is 3.9%. So Current MPG X 1.039 = Actual MPG

It still doesn't seem like your mpg should be down in the teens though. Other things could be low tire PSI or a heavier right foot.

 

Yeah...Make sure you are doing the correction to the mileage. Cause a 10 MPG drop is pretty intense.
Also check the pressure with the chalk line test.

 

Its amazing how much a bigger more aggressive tire can mess with the MPG. Like afd23a said the winter blends of Gas do suck aswell, so the odds are against us I'm running a 265/75/16 but i'm about to step up to the 285s so i'll be in your same boat soon. Get a after market drop in air filter like the AFE Pro Dry-S...anything that can increase your fuel economy is a plus

 

Thanks for all the info. I think it is a mix of everything. The rolling resistance, weight, cruddy fuel and a right foot that could be a little lighter. I'll keep an eye on it over the next few weeks and see if things get better. I usually don't drive all that fast but I had so much driving over the last week I was probably trying to get "there" a little faster than I should have. The truck looks pretty good with the new tires though

 

i just put the same size tire on mine as well and my mpg dropped from 26 to about 24

 

Ya, you're not alone man. I "upgraded" to 265s bfg all terrains and I get about 19 mpg....but the bigger tires def. Look better

 

well I changed from HT to AT and lost 1 mpg and when I changed from 265-70/16 to 265-75/16 I lost 2 mpg and when I s/c I lost 2mpg so yeah Im at 18 mpg

 

The stock at20 are good for a lot of "generalized" driving with good mpg imo.
go to an all terrrain -1
larger tire and more rotational mass -1
winter fuel -2
more traction/friction -1
this is of course a generalization
I stayed with 245/75/16 for my winter tires and saw a 4 mpg drop ,with the combined factors.

 

I can tell you that I upgraded to 35 inch Mud Terrains from the stock 265's on my old truck... I went from 17 mpg to a whopping 10 mpg... It sucked

 

Yup, another one with this issue.

I just put a set of Duratracs on my 4bannger, 4x4, and noticed a drop. Same size as stock (245/75/16) yet the heavy tries cause my spedo to read 5km faster and a drop in mpg.

However, i just did my first fuelly, and im getting what the EPA states i should get...so, i guess i cant really be mad. Ill wait till summer to see if it goes up a bit.

 

Yeah, I think I'll wait to see what happens this summer. For now, it just cost a little more, unfortunately I seem to be driving more now than I ever have before

 

When I had my 5-lugger I replaced the stock tires with a larger size at about an Inch taller. Made the SPEEDO right on but mileage now reflected a lower number because of it.
Combined with thegearing being taller because of the tires my mileage went from an average of 21 down to 18 and It struggled on some of the hills here in south OC.
So I said screw it and got a V6 PreRunner that gets 18 mpg and a lot more fun to just cruise up the hills rather than floor it.

 

I hear ya. Somewhat feeling the same way. I justified getting away with a 4bang with lack of towing, but im starting to think that the little guys really cant deal with a good power/gas/hauling combo. Not to mention bigger tires.

Oh well. I still love her so.
Just giver

 

Hey, this recently happened to me.. I went from stock duellers to the revo 2s. The tire place first put my tires to only 28 psi, wtf? These tires were wandering soo bad on the highway at 60+. I had my stock duellers set to 31psi and got 22+mpgs so I aired these up to 33psi but still TERRIBLE mileage. So yesterday I aired them all up to 37 psi. The truck feels much better and I actually feel like the truck is peppier. I think AT tires need to ne aired up considerably more than the stock street tires so try that for a tank and see if it helps, its already helped me a ton on the tank I've been driving on.

 

Winter temperatures affect overall mileage as much as 30% Winter fuels having 1.wahatever% less energy is not even a talking point (20mpg X .985= 19.6 mpg...)
The Dunlops are an incredibly low rolling resistance tire, and 245`s roll easy with less wind resistance than 265s. I estimate my bfg`s cost at least 1 mpg, and I didn`t increase size.