Unexpected impact of bigger tires

[calemasters]

Does the transmission still reach 8th gear at highway speeds?

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[zouch]

sounds like the difference in tread pattern/rolling resistance.

what did you use to calibrate for sizes? and how did you do it?

Two months ago, I switched from 35” Mickey Thompson Baja MTZs to 37” BFG KO2s. The decision was helped by the fact that the unsprung weight was nearly identical—65 lbs versus 66 lbs.

I wasn’t concerned about gearing because the vehicle is driven exclusively on-road, and with a close-ratio eight-speed transmission, the only potential downside would be initial takeoff in first gear. With 442 lb-ft of torque available at 1,400 rpm, that proved to be essentially imperceptible.

I’m a creature of habit and my driving patterns are very consistent, which made it easy to evaluate the impact on fuel economy. Surprisingly, mileage has increased by roughly 10–15%.

????

 

[jeepingib]

Better efficiency from the tread and lower RPM without increasing the load. Yeah, I can see a small improvement being real.

 

[AskBin]

Surprisingly, mileage has increased by roughly 10–15%.

youve essentially geared down for the highway, and given the turbo more to do. turbos like work and load, and youve given it more to do. looks like that translates to a more efficent curve on the fuel map

 

[raven_the_moab]

I was contemplating the same - 35" --> 37" - after upgrading the suspension on my 21' EcoD. I saw that the gearing chart showed a recommended move from 4.10 beyond 35". I was wondering with the diesel given the better low end torque. Glad to hear.

 

[roaniecowpony]

sounds like the difference in tread pattern/rolling resistance.

what did you use to calibrate for sizes? and how did you do it?

I agree 100%. A new mud tread tire has terrible rolling resistance, let alone a worn one. I went thru this on my pickup many years ago.

For another perspective @SadRobot went from a 37 BFG K02 to a 37 Cooper STT Pro this past year and lost fuel economy. Maybe she can quantify that.

 

[Terrymo]

I agree 100%. A new mud tread tire has terrible rolling resistance, let alone a worn one. I went thru this on my pickup many years ago.

For another perspective @SadRobot went from a 37 BFG K02 to a 37 Cooper STT Pro this past year and lost fuel economy. Maybe she can quantify that.

I swore when I first switched from the OEM BFG 315s to the 37” Mickey Thompson MTs I could feel the lugs (like driving on cobblestone) at very slow speeds. Maybe my imagination. I try not to look at my MPGs or the gas prices at the pump…ignorance is bliss.

 

[jaymz]

Okay guy, fuck years of everyone coming to the same measurements, its about the time someone like you showed up and sprinkled us with facts. Rejoice offroad community!

To be fair, 3TV backed up his statement with proof. You? Not so much.

 

[AskBin]

I could feel the lugs (like driving on cobblestone) at very slow speeds. Maybe my imagination.

i noticed this too, the factory M/Ts on the willys are horrible IMO like would visibly vibrate my mirrors at low speeds. 30k miles and I had to go to A/Ts, dosent feel like im constantly driving in Phili now...

 

[Terrymo]

i noticed this too, the factory M/Ts on the willys are horrible IMO like would visibly vibrate my mirrors at low speeds. 30k miles and I had to go to A/Ts, dosent feel like im constantly driving in Phili now...

Mine either broke in or my brain blocked out the difference over time. I am super happy with the tires offroad though

 

[AskBin]

Mine either broke in or my brain blocked out the difference over time. I am super happy with the tires offroad though

probably broke in and you do proper rotations. who knows what the original owner of my car did to wear mine down to 4/32nds in 22k miles

 

[SadRobot]

I agree 100%. A new mud tread tire has terrible rolling resistance, let alone a worn one. I went thru this on my pickup many years ago.

For another perspective @SadRobot went from a 37 BFG K02 to a 37 Cooper STT Pro this past year and lost fuel economy. Maybe she can quantify that.

I went from about 18 mpg with the KO2s to about 15 mpg with the Coopers. When it was my daily driver it got just a little over 200 miles on a tank. I had to fill it up 3X a week which averaged about $750/month in gas.

 

[grimmjeeper]

Two months ago, I switched from 35” Mickey Thompson Baja MTZs to 37” BFG KO2s. The decision was helped by the fact that the unsprung weight was nearly identical—65 lbs versus 66 lbs.

I wasn’t concerned about gearing because the vehicle is driven exclusively on-road, and with a close-ratio eight-speed transmission, the only potential downside would be initial takeoff in first gear. With 442 lb-ft of torque available at 1,400 rpm, that proved to be essentially imperceptible.

I’m a creature of habit and my driving patterns are very consistent, which made it easy to evaluate the impact on fuel economy. Surprisingly, mileage has increased by roughly 10–15%.

????

My money is that you are benefitting from lower RPMs at highway speed. Diesels do well at low RPM. Combine that with a tire that has less rolling resistance and the mileage increase is easy to understand.

You have the factory 3.73s still?

 

[Terrymo]

I went from about 18 mpg with the KO2s to about 15 mpg with the Coopers. When it was my daily driver it got just a little over 200 miles on a tank. I had to fill it up 3X a week which averaged about $750/month in gas.

If gas prices get any higher I’m going to need to start moving bricks for El Chapo. I’ve watched that Clint Eastwood movie, The Mule, a few times just to get some pointers.

 

[SadRobot]

If gas prices get any higher I’m going to need to start moving bricks for El Chapo. I’ve watched that Clint Eastwood movie, The Mule, a few times just to get some pointers.

I guess I’m just happy we’re still under $5/gallon.

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