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Got OEM Grabber AT2's and MPG dropped 4mpg!?

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inv3ctiv3

NAXJA Forum User
Location
Santa Barbara, CA
So my old tires were tottaly bald and wore out so I ordered some General Grabber AT2's in 225/75/15 and threw them on. It drives great now (no wobble or shake) but I've noticed my MPG has dropped drastically! I was averaging 300-325/tank and now I am averaging 240-250/tank! Are the grabbers super heavy or something? I also changed my oil but used Mobil 1 10w30 Synthetic (fram filter which I plan on changing out since I read they are garbage).

Has anyone else experienced this? The jeep is totally stock otherwise....

2001 Cherokee Sport - 4.0 and auto
 
Had a buddy looking into the red letter grabbers, a 33" weighed.as much.as a 35" bfg km2

Check mfg websites, if you dig deep enough, they will have tire weights
 
Miles per tank means nothing, kinda like hamburgers per picnic. You need to calculate miles per gallon for 3-5 gas tank refills.

Area all your tune-up parts fresh ? How old are your O2 sensors ? An unexplained drop od 30% or more in you Miles Per Gallon, is most often a weak or failing O2 sensors.
 
Tim_MN said:
Miles per tank means nothing, kinda like hamburgers per picnic. You need to calculate miles per gallon for 3-5 gas tank refills.

Area all your tune-up parts fresh ? How old are your O2 sensors ? An unexplained drop od 30% or more in you Miles Per Gallon, is most often a weak or failing O2 sensors.
Click to expand...

I just bought the car and it came with a smog cert and passed fine, if they aren't too expensive I could just replace them to be safe since it has a 135k miles.

I do calculate miles per gallon, I fill up, reset my trip, drive till the light comes on, fill up and see how many gallons went in and divide the miles I drove by that number. So if I drove 243 miles in 17.8 gallons that's what I use to divide.
 
243/17.8 = 13.65 mpg. Not that great, but within what one might expect for an XJ. EPA rating is 16 city and 20 hwy, both of which are generous numbers.

Tune-up, clean up the Throttle Body and the injectors, test the O2 sensors and the Coolant Temperature Sensor.
 
Tim_MN said:
243/17.8 = 13.65 mpg. Not that great, but within what one might expect for an XJ. EPA rating is 16 city and 20 hwy, both of which are generous numbers.

Tune-up, clean up the Throttle Body and the injectors, test the O2 sensors and the Coolant Temperature Sensor.
Click to expand...

I mean something happened within a week of getting the tires, it was averaging 18-19mpg and I'm doing the same drive (mostly highway) so that hasn't changed. I gotta figure this out though because that is a HUGE drop.
 
Tune-up, clean up the Throttle Body and the injectors, test the O2 sensors and the Coolant Temperature Sensor.
 
Worth a shot
if you are getting sub 14 mpg on a stocker, something is wrong
as.suggested before, a tune up and O2 sensors would be a good start
 
Grab a stock size tire and rim off of of Craigslist for cheap and see if your mileage returns to normal. If so, you've found your answer for both weight and mileage. If it is a heavier tire im sure you would also notice you breaks having to work harder. More momentum takes more to stop.
 
Keep in mind that new tires will have a bigger outer circumference (more tread) and because they have more tread will have more weight. This weight is also at the worst spot which is as far from the wheel center as possible. Do a search on google through other car forums and might find the same problem across makes.

Also, are the old and new tires the same ply construction and load rating? A 6 ply will be heavier than a 4 ply and will have a higher load rating.

Some tires are inherently heavier than others. For example, I have noticed that Hankook A/T tires are usually pretty heavy compared to other manufacturers.
 
Tim_MN said:
How old are your O2 sensors ? An unexplained drop od 30% or more in you Miles Per Gallon, is most often a weak or failing O2 sensors.
Click to expand...

I just got a 2000 gmc 2500 with 180K on the 6.0, it gets 10-12 mpg around town, it's a 100% stock And has 5 O2 sensors... I literally just got a CEL for the O2 sensor, I wonder if just to be safe if I should just change all of them... the PO never changed the plugs either.
 
If you went from TOTALLY bald tires to new tires with 16/32 of tread, this could account for some of the difference. The bald tires would require you actually drive further (smaller diameter), and falsely increase mpgs. They would also turn easier (require less power) being smaller and lighter.

I can see the 1" difference in diameter accounting for maybe a 30 mile difference in odometer reading and throw calcuations off by 1-2mpgs (guessing closer to 1 mpg). And if you lose another 1-2 due to the tire being heavier, then your calculations are spot on.

Perform a tune-up, make sure everything else works on the Jeep, and take it easy on the skinny pedal!
 
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Does CA have summer blend and winter blend gasoline ? Did they change over about the same time you noticed the mpg drop ?



redneck said:
Grab a stock size tire and rim off of of Craigslist for cheap and see if your mileage returns to normal. If so, you've found your answer for both weight and mileage. If it is a heavier tire im sure you would also notice you breaks having to work harder. More momentum takes more to stop.
Click to expand...

225/75/15 is within a few % of the stock original size tires, thus mpg calculation would only be off few %. Going from stock tires to 31 x 10.5 tires only makes your calculations off by about 5%.
 
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I don't really care, though. I LOVE these tires. Very, very stoked with wet, dry, dirt and sand performance so far.

Sidewalls seem tough enough for my uses. (use, not abuse)
 
quite often, sudden drops in MPG are due to a bad o2, but not always. do you have a cracked exhauast manifold?
you have a 2001, so you have like 4 o2 sensors, you might want to price out some sensors if they havent been replaced in a while.

if they are bigger than the other tires the ODO will be off , so calculate your actual driven miles and then use the actual gas used by topping it and tracking it all.

check tire pressure/exhaust leaks/vacuum leaks/grounds/sensor connections.
do a tuneup too.
plugs/plug wires/o2 sensor(s) /clean out TB/ acetone in the gas tank/ fuel filter/air filter/ test TPS/oil change with some MMO and tranny fluid, run it for 50-100 miles and change it again/ if auto tranny drain and refill tranny pan/check brakes for brake drag/

get rid of the fram right away. use WIX, napa gold is WIX i believe. thats all I use.
 
Check your tire pressures.

Under-inflated tires will rob your mileage.

As stated, o2 sensors tend to become "weak" and your mileage will drop off yet NO CEL and you may still pass SMOG inspections, but your mileage will suffer. I am a fan of the NTK (NGK) 02 sensors, even though Bosch has a good reputation.

Check your belt driven accessories--a failing power steering pump can really rob you.

Replacing stock size tires with stock size tires SHOULDN'T have a large impact on your mileage. As stated, check your tire pressures, and if those are Ok you need to look at other issues.

FTW: JP Magazine ran a series on XJ fuel mileage:

http://www.jpmagazine.com/projectbuild/154_0808_building_a_fuel_efficient_jeep/index.html


http://www.jpmagazine.com/projectbuild/154_0810_building_a_fuel_efficient_jeep_part_2/index.html


http://www.jpmagazine.com/projectbu...cherokee_xj_project_mileage_master/index.html
 
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I have a simular issue. My cherokee use to get 15 mpg avg on street 225 70s. I went to bf goodrich all terrains and lost a soild 2 mpg on 235 75 15s. But its been like that for the last 4 years. My jeep is upkept well also. Just nature of the beast I guess. When I lost the MPG at first years ago I went as far as buying new injectors and fuel pressure regulator and still nothing gained back.
 
Well I'm leaving on a business trip for almost two weeks so I won't be able to address anything for a bit. I really should just buy new O2 sensors anyway, NGK or Bosch? I'm also going to be re-doing the cooling system and belts so I'll inspect everything then. Maybe run some BF44k when I get back and see if that helps too. Thanks for all the suggestions!
 
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