Fuel Economy - LT Tires or Temperatures ?

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MarineBSP

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Sharing my personal experience for a 2018 Laramie 5.7L Hemi CCSB, running 275/65R20 LT tires in place of the OE 275/60R20 P series tires. First, I used AlfaOBD and adjusted for the larger tire diameter compared to the OE 60-series tires, so speedometer and mileage are pretty accurate.

I have been running LT tires for about 16 months - first this size in winter tires, and then a second set of LT tires (AT's) on a second set of rims as 3-season tires. I decided to do this based upon enough winter freeway metro driving that I want the extra bite on ice and slushy snow. So after this year's wimpy winter and some other variables I discovered a few things:

1) When I first switched to LT tires in the larger size I ran them at about 47 PSI - I have now gone to 55 PSI without noticing any harsher ride.
2) Initially I thought these tires lost me between 1 and 2 mpg - maybe a little more. As you will see, I have changed my mind on the tires being the main culprit.
3) This past year we demolished and re-built our detached garage here in Minnesota. My truck was in a 'temporary garage' (open ended tent) most of the Winter, getting as low as 16 mpg on one tank of fuel. That is mostly highway with some city driving, but keep in mind that I don't live very close to much, so most places are are 30 miles away or more.
4) I have paid close attention to coolant, transmission, and oil temps - on the average in the Winter my truck's heart and lungs are not warmed to operating temps for at least 10, sometimes 15 miles.
5) In February, just as we had a week of < -20F low temps, I finally could put my truck into a heated garage. The truck could now start trips from home at 65F instead of -20F. Wow ! Mileage went way up! This was on the same 'winter blend' fuel - just way better mpg.

I don't particularly trust the EVIC fuel economy, but I am quoting the cumulative "mpg" recorded for each trip (trip = 1 tank) that I observed with changes in outside temperature and with changes in STARTING temperature. As mentioned earlier, for one tank I got an even 16.0 mpg when the truck started from cold (usually about -10F to 0 F). Running in -20F to 0F temps but STARTING trips at 65F from the garage the next tank was well over 18 mpg.

The winter tires are about to come off, but I have recorded three tanks of 19 to 21 mpg with these tires as the temps have gotten warmer. I never did any better with the OE P276/60R20 Goodyears. I am sure the LT tire with AT treads will take back some of my mpg again - partly it's tread squirm and partly it's tire weight.

My experience suggests that the big mileage killer in Winter is not fuel and not the LT tire size itself, but the time it takes to get the grease, oil, ATF, coolant, and tires up to temp. The LT tires are heavier than the P series tires, so it figures they would be harder to flex when cold.
 

tidefan1967

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Sharing my personal experience for a 2018 Laramie 5.7L Hemi CCSB, running 275/65R20 LT tires in place of the OE 275/60R20 P series tires. First, I used AlfaOBD and adjusted for the larger tire diameter compared to the OE 60-series tires, so speedometer and mileage are pretty accurate.

I have been running LT tires for about 16 months - first this size in winter tires, and then a second set of LT tires (AT's) on a second set of rims as 3-season tires. I decided to do this based upon enough winter freeway metro driving that I want the extra bite on ice and slushy snow. So after this year's wimpy winter and some other variables I discovered a few things:

1) When I first switched to LT tires in the larger size I ran them at about 47 PSI - I have now gone to 55 PSI without noticing any harsher ride.
2) Initially I thought these tires lost me between 1 and 2 mpg - maybe a little more. As you will see, I have changed my mind on the tires being the main culprit.
3) This past year we demolished and re-built our detached garage here in Minnesota. My truck was in a 'temporary garage' (open ended tent) most of the Winter, getting as low as 16 mpg on one tank of fuel. That is mostly highway with some city driving, but keep in mind that I don't live very close to much, so most places are are 30 miles away or more.
4) I have paid close attention to coolant, transmission, and oil temps - on the average in the Winter my truck's heart and lungs are not warmed to operating temps for at least 10, sometimes 15 miles.
5) In February, just as we had a week of < -20F low temps, I finally could put my truck into a heated garage. The truck could now start trips from home at 65F instead of -20F. Wow ! Mileage went way up! This was on the same 'winter blend' fuel - just way better mpg.

I don't particularly trust the EVIC fuel economy, but I am quoting the cumulative "mpg" recorded for each trip (trip = 1 tank) that I observed with changes in outside temperature and with changes in STARTING temperature. As mentioned earlier, for one tank I got an even 16.0 mpg when the truck started from cold (usually about -10F to 0 F). Running in -20F to 0F temps but STARTING trips at 65F from the garage the next tank was well over 18 mpg.

The winter tires are about to come off, but I have recorded three tanks of 19 to 21 mpg with these tires as the temps have gotten warmer. I never did any better with the OE P276/60R20 Goodyears. I am sure the LT tire with AT treads will take back some of my mpg again - partly it's tread squirm and partly it's tire weight.

My experience suggests that the big mileage killer in Winter is not fuel and not the LT tire size itself, but the time it takes to get the grease, oil, ATF, coolant, and tires up to temp. The LT tires are heavier than the P series tires, so it figures they would be harder to flex when cold.
Great observations but if I had to guess I would say the switch to winter fuel(more butane) and more idling are just as big a cuplrit to poor mileage as lifts or LT or AT tires.
 

crash68

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I see the same with a diesel but that a little bit more expected, the faster it gets up to temperature the better the overall fuel economy.
Even for the gas truck if your going to be in teens or even colder, it might help using the Mopar winter front cover not only fuel economy but faster occupant comfort also.
Mopar winter front cover: 82213959AC
 

GRN69CHV

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I'd be real happy with 16 mpg average. With exception of handful of long drives I've take, I can't seem to get over low 15's, high 14's in winter. In this area, longest highway run I ever seem to make is maybe 15-20 miles before exiting and then back into urban stop and go traffic.
 
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