After a few weeks with BFG mudders, our 2012 Jeep Wrangler is returning the sort of fuel economy you might expect. We averaged 17.5 mpg on stock wheels and tires for the first 5,000 miles of the test. Upgrading to the 17-inch rims and 33-inch tires has us averaging 15.6 mpg. Down about 2 mpg.
We don't have a large sample size to work with yet. This mileage calculation includes just over 300 miles and 3 fill-ups with the new setup. But it gives an idea as to the fuel economy outlook at this stage in the modification process.
Mike Schmidt, Vehicle Testing Manager @ 6,559 miles
bassrockerx says:
03:46 AM, 12/30/11
maybe when you regear the axles you will get 1mpg more but it is still overall going to be a loss. still not bad overall considering your driving mostly in l.a traffic and what not seems like all your cars get crap mpg due to traffic. those wheels look amazing if it means sacrificing 2 mpg then so be it!
alanscott1 says:
04:25 AM, 12/30/11
Not sure how much your tires weigh but I went with a set of 33" Goodyear Duratracs on my 2012 JK w/3.21 gearing. Before the swap I was averaging about 19mpg, with the new rubber Im getting about 17.5-18mpg. I was really surprised by this, I too was expecting a big hit in mileage. The added stability of the new tires is nothing sort of amazing compared to stock too!
adamb1 says:
05:53 AM, 12/30/11
What have you done to compensate for the fact that the odometer is reading incorrectly with the larger tire size in you computation of fuel econonmy?
alanscott1 says:
06:19 AM, 12/30/11
I personally went with an AEV procal module, to correct for the larger tire size.
kain77 says:
06:29 AM, 12/30/11
@adamb1
Great question. Is IL factoring for the ODO being off when calculating MPG?
addicted2sp33d says:
08:08 AM, 12/30/11
+1 for adamb1 and kain77.
When I swapped out my stock tires for tires with a noticeably larger rotational circumference, I noticed a decrease in the "mileage", but once I compensated for the larger rotational circumference, I really didn't take any mileage hit, and was actually marginally better; probably because for any given "real" speed with "real" air resistance, the motor was actually spinning just a bit slower.
I made quite a jump in tire size, and my correction factor turned out to be about 1.1 "real" miles to every 1.0 odometer miles.
Most cars' odometers really only count "axle rotations" or "brake disc rotations"... e.g. 800 rotations = 1 mile.
If you put on bigger tires, you end up with say 750 rotations per mile. You travel same 1 mile, but now it only takes 750 rotations to do it, your car's odometer will only register 0.94 miles.
I also did this to fix a 10% mph differential that I found on my wife's VW Beetle. The odometer and speedometer were spinning about 10% faster than what my GPS was telling me. The VW odometer was aging the car faster than reality!
Of course you can measure the differential with any GPS app that records "distance traveled", and the larger distance that you use for your measurement, the more-accurate your odometer differential-calculation will-be. I used a 450-mile drive from San Diego to San Francisco.
shaddai says:
09:09 AM, 12/30/11
300 miles and 3 fill ups?
100 miles per tank?
(I'm guessing they were partial fills, but...?)
miamifan1 says:
12:31 AM, 12/31/11
i'm loving the new setup. its perfect, now.
i know your mods are just beginning, and i do look forward to moar testing. but, frozen in time, this is how i would leave it.