Got some bigger tires and mileage is now horrible

Hi there.

Wondering if anyone has any thoughts on this.
I have a 1996 tacoma with a 2.7 4 cylinder in it. 3RZFE

I have a short commute in the city. Up until recently I was getting around 16 mpg on 235/75/15 tires. Stock is 225/75/15 so only very slightly wider and taller than stock.

I recently got a good deal on some 4 runner rims and some stock tires off a 2021 Tacoma. The new tire size is 245/75/17.
For the last two tanks of gas my mileage has dropped to 11MPG!? The tires size is 9% different and the odometer runs off the speedo cable so even taking that into account it's still only 12MPG.

Has anyone had this same issue before? Maybe just a bit too much rotational weight for the 4 cylinder to get moving?

I haven't changed anything other than the wheels and tires. Air filter is clean, MAFS is clean, tire pressure is correct, same commute, same gas.

235/75/15 16 mpg 240 Miles on 15 gallons
245/75/17 12 mpg 165 Miles on 15 gallons


Thanks for looking.

 

I am pretty sure your speedometer and odometer is now off that you switched up your rim size meaning that the miles you get per tank is inaccurate. Presumably this means you have traveled further than what your odometer reads. Additionally, I believe it takes more power (gas) to spin those larger wheels. I'd look into a conversion calculator for changing your rims to see what the actual mph and mileage is per tank.

 

Hey thanks for the message. I did the conversion and it's only a 9% difference in tire size which doesn't account for the majority of the loss. So that would make the 11mpg 12mpg. And the 165 miles per tank 180.

 

If you've changed nothing but the tires, it's the tires.

 

Very surprising outcome. Shouldn’t bigger round thingys make truck go farther. This fysicks stuf is treadchorouse.

 

-Loudboy

That's what I'm thinking as well. Hoping someone who has upsized their tires with a 3RZFE will be able to weigh in. If they didn't have the same drastic change I will know it may be something else and just a maybe just a coincidence with the tire swap...

 

Rim size make no difference, it's the tire size that will change the mpg.

OP, you went from a ~28ish inch tire to a ~31ish tire. Plus, the weight of the new tires and weight of the new rim are probably heavier than your orginal set. All that will drop your mpg

 

Which tires? What load rating?

 

What he said

 

^^^This^^^ it's all physics. Heavy tread is now further away from axis of rotation which requires more effort to get it spinning and keep it spinning. In MTB riding, 1 lb saved in wheel weight (rotating weight) was about equal to 5 lbs on your bike frame.

 

The smaller tires were BF goodrich KO's, the bigger ones are toyo open country 3's. Not sure of the load rating but I can't see how that would affect mileage?

 

What's your differential ratio as well? That could also have an impact on this

 

I agree that it would drop my mileage. But I just can't see that it would drop it that much...I've done some looking around on the internet and it seems way higher than it should be. This is a major reduction in fuel economy.

https://www.dunntire.com/blog/Does-...r, power and economy are,mpg due to tire size.

 

Load rating will tell us the weight difference between the original and the new tires.

Tire is taller, likely heavier, and has more rolling resistance. Not to mention we're working with a 4cyl that doesn't create much torque to begin with. It's the tires.

 

It's not even FRIDAY yet. If rims and tires are the last/most recent add on you did to your truck, that's your issue.

 

I'll disagree with you on the rim size not making a difference. I have a VW Jetta TDI that I get 50-55 mpg with. I did months of research on how to squeeze the best mpgs out of the car I could. One thing that was consistently found to be true, was a larger rim, even with the same overall tire diameter got worse mpg than the smaller rim. I believe it to be because the barrel of the rim is further from the axis of rotation, and the barrel is a significant amount of mass in relation to total weight of a rim.

 

Weight of the rim will affect mpg. But if both rims weighing the same, just diffential size (16 vs 17) that will not affect mpg.

 

OP, you kind of double whammied your mpgs with a larger rim size AND a larger tire. 4 cylinder engines suffer a lot from any kind of resistance, be it wind, weight, rolling, etc...

I've played this game with my '02 diesel Jetta for quite some time trying to best my record mpg's. I average 50-55 and bested at 60.4 once. Just a tick over 900 miles on 15 gallons.

Going from a 15" rim to a 17" rim moves the barrel of the rim farther from the axis of rotation and a 4 cylinder will notice it. The wider tire also weighs more, creates more rolling resistance due to larger contact patch as well as a larger overall diameter. So really it's a triple whammy on your mpg's. Tread pattern and sidewall rating also have an impact on mpg's. If the new rims have a lower offset and make the tires stick out more, that too can have an impact.

 

If nothing else, riding a bicycle makes you appreciate how much of a difference rotational unsprung weight affects efficiency. Heavier tires are incredibly deleterious to mileage and acceleration, even more so with an increased diameter. I ditched my BFG kos for some firestone Destination XT's. The 4 cylinder is particularly unable to utilize heavier wheels.