Low MPG with 33s R18 load E tires

[Lioska]

Hi, wondering if anyone else is in the same situation. I got Nittos grappler tires 275/70/18 load E on stock Sahara wheels and I am getting about 15 mpg (mostly city) with no lift or mods.

I noticed the tires are about 58 lbs each and I have seen 285/70/17 load C at around 38 pounds (20 lbs difference).

Is it right to assume the additional weight on the tires are the main reason for the low MPG or that's expected for mostly city driving ?

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[Maverick909]

Looks like you have a sport in your profile pic. Have you recalibrated the ecu? If not your Jeep is going to loose mpg quite a bit as the engine module needs correct information to shift the transmission correctly for the tire and gear sizing. I’m am currently running 4.10s and 33” tires and avg 20mpg on my last overlanding trip of 1500 miles. Including over 500 miles of dirt travel

 

[grimmjeeper]

X2 on recalibrating your computer for the new tire size. Your speedometer will read low (along with mileage) until you do.

 

[aldo98229]

I had 275/70R18 KO2s on my Sahara: didn’t see an impact on MPG.

Now that I got a lift and 35-inch tires, I do.

 

[mwilk012]

The calibration isn’t the problem, your heavy foot and admittedly mostly city driving is the problem.

 

[Black Jeep Convertible]

Hi, wondering if anyone else is in the same situation. I got Nittos grappler tires 275/70/18 load E on stock Sahara wheels and I am getting about 15 mpg (mostly city) with no lift or mods.

I noticed the tires are about 58 lbs each and I have seen 285/70/17 load C at around 38 pounds (20 lbs difference).

Is it right to assume the additional weight on the tires are the main reason for the low MPG or that's expected for mostly city driving ?

Did you reprogram your new tire size? If not, do that first with tazer https://amzn.to/3wIlHZ7

 

[Lioska]

Thanks for the replies, I have a sport altitude that came with 32s tires so would the difference from 32s to 33s be big enough to impact the transmission shift and MPG? Do people that move from 32s to 33s usually use the tazer?

I don't drive aggressively but will try to watch it more closely to see if that makes a difference.

 

[Lioska]

I had 275/70R18 KO2s on my Sahara: didn’t see an impact on MPG.

Now that I got a lift and 35-inch tires, I do.

Did you use the tazer when you installed the 275/70R18?

 

[liquids]

Lots of rotational inertia in heavy tires. The starts and stops of city driving require lots of energy to spin them up and lose lot of energy in heat loss off the brakes. Highway driving probably wouldn't have as much of a hit to your mileage.

 

[BlackGenesis]

Recalibrating does not make difference in MPG. It now takes more gas input to accelerate at the samerate as beforehand, hence your city mpg Is worse. Higher wheel weight at greater distance from center of rotation is your enemy.

I believe Firestone destination X/T is the lightest tire you will find in the side of 275/70.

 

[grimmjeeper]

If you don't recalibrate you will log fewer miles so it absolutely will affect the mileage on your dash. City vs highway driving will affect your mileage. Aggressive acceleration will lower your mileage. Driving really fast on the highway (over 75) will really hit your mileage.

And the dash gauge is never accurate to begin with.

If you want true mileage, get a GPS to get true distance and calculate your mileage manually.

 

[aldo98229]

Did you use the tazer when you installed the 275/70R18?

Didn’t have to. The speedometer came off by 1.5 MPH from the factory; it was right on the mark with the 33-inch tires.

 

[Black Jeep Convertible]

Didn’t have to. The speedometer came off by 1.5 MPH from the factory; it was right on the mark with the 33-inch tires.

If you want a more accurate reading you’re going to have to

 

[aldo98229]

If you want a more accurate reading you’re going to have to

Apparently I didn’t say it well.

So here is another try:

• Jeep came with 32s; speedometer was off by 1.5 MPH —I checked my speed multiple times against radar.
• Replaced OE tires with 33s; speedometer reading became spot-on without a Tazer

Now I got 35s: the tires measure 34.5 inches mounted, but had to set the Tazer at 33.75 to get an accurate speedo reading.

It appears the Jeep’s tire size calibration settings are off by about 0.75 inches.

 

[DirtRoad]

My Sport came with 245/75/17 Good Year Wranglers (a very light tire that measured 31.25" with weight on them). I put 285/70/17 Bridgestone A/T's on it (also a pretty light tire that measures about 32.25" with weight on). Checked speedo against GPS and it was about 5% fast with the stock tires and about 5% slow with the new ones. I didn't notice much of an MPG hit with the new tires but they're lighter than yours. I'd say for that tire size change, recalibrating the speedo is sort of optional. It seems pretty common for manufacturers for set the speedo just a little fast with stock tires. It makes your warranty run out a little faster, at least if you drive an average amount or more.

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