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I'm getting better mileage on 37's than i was with 35's!

Jt-wrx

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First, the jeep.
Sport S, 6-speed

Started with 315 70r17 goodyear duratracs on mickey thompson classic III's (62 lbs on 28 lbs), 4.5" back spacing on mopar lift. Averaged over 10 tanks of fuel 15.2 liters per hundred km (about 15.5 mpg), granted, winter.

Made the change to factory wheels with 37x12.50 falken mt's (82 lbs on 23 lbs), added 12mm die cast spacers to mimick wide axle max tow/rubicon width, also added 3/4" strut spacers to the front end, and just fyi...used 4 washers under drivers side steering stop to stop control arm rub, used 5 spacers under passenger side steering stop to do the same.

3 tanks of fuel over 1260 kms and i'm at 14.2 l/100 km or 16.5 mpg!

measured treadwidth of the 35's was 10.5" and i ran at about 32 psi, measured tread width of the 37's is 10" and running about 29 psi

So my theory is that even though i'm taller and heavier, the combination of less tread width and not having at least 2" of rubber sticking out into the fresh air is more important than the weight/diameter?

Anyone else have thoughts? Or similar experience?

Mine can be seen on Instagram @gladiatoryyc

Maybe tire pressure still a little too high and i'm not riding on full tread width?

Either way i feel i'm done with build, loving the heck out of this set up. Tall and skinny and saving piles on car washes as i'm poking only side wall into the fresh air. The tops of the fenders just catching the outer edge of the spray so one puddle doesn't waste $8. ;) Loving this so much more!

Edit! Tazer JL Mini used to correct speedo to gps at 80 mph for both sets of tires so this info is valid, all is hand calculated (the computer averages 2% error fyi and usually to the 'look good side')...settings required for the 35's was 34.44 and for these 37's needed 36.45.
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Jt-wrx

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update, 4 tanks of fuel, average over 1666 kms, 1035 miles...has been 14.4 l/100km or 16.3 mpg, driving has been pretty chill and relaxed.
 
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Mine is going up, too. Brand new, and 100% stock mine averaged like 11.5 MPG... Noticeably heavier 37x13.50’s on 20x10 wheels, Tazer recalibration for tires, and an iDrive unit, and it’s up to 12.5, and slowly climbing. I never run interstate hardly, and I live in a very hilly area, so quick short trips up and down hilly backroads at 45-55 MPH, I don’t feel 12.5 MPG average to be all that bad. And I do drive a bit aggressively on the throttle (have to) to maintain speed going up and down those long hills. :like:
 

skull_squadron

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Did you correct speedometer for the new tire size OP?
 

FreedomWV

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I've experienced the same. I've put about 300 miles on mine since going from 285/75r17 to 37x12/50r17 which is quite a difference in weight and size. I was averaging around 15.3 previously and I reset my mpg's the day I put them on and now around 18.4. I also have a tazer and my mph is exactly on per gps speedometers. It doesn't make logical sense but it is what it is. I keep a fairly close eye on my mpg's.
 

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JTGuy

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I am also getting about 1 MPG better with my 37s than I did with the 315s. But, I did re gear to 4.88s.
 

GA D90

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I've experienced the same. I've put about 300 miles on mine since going from 285/75r17 to 37x12/50r17 which is quite a difference in weight and size. I was averaging around 15.3 previously and I reset my mpg's the day I put them on and now around 18.4. I also have a tazer and my mph is exactly on per gps speedometers. It doesn't make logical sense but it is what it is. I keep a fairly close eye on my mpg's.
Are you guy's using stock wheels with the 37's ??
 

FreedomWV

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Are you guy's using stock wheels with the 37's ??
I got a good deal on a set of wheels and tires from the marketplace. I am running warn 17x8.5 wheels and 37x12.50r17 falken wildpeaks.
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