the easiest way to know your actual speedo error is of course GPS. as for individual calculations, just PM me and I'll calculate for you what your actual mileage is with oversize tires. i did for 31x10.5x15. my error is 1.109. ie, for every 100 miles on the odometer i've actually driven 110.9 miles

 

1997 dead stock in town/hwy mix = 20 mpg
driving normal not easy or hard

4.0 - 5 speed - 235-75-15
3.07 gears

 

96, 3" lift, 34k, aw-4, 31" tires, customer bumpers(kinda heavy) c17/h21. There is more to life than fuel mileage that's what honda's are for.

 

7-9mpgs city. I have a 3in lift and 31s.

 

'96 Cherokee
149,800
225/75/15
speed limit, or slightly above. With the occasional burst into the 4,500+ rpm range (because I can)
Nothing aftermarket other than platinums and 8mm wires
City/Hwy ratio: 25% / 75%, 20 mpg /25 mpg, 24 overall

* 2.5l 4-banger w/AX5 (it DOES move when you punch it )

 

HAHHAAA. I DID IT. 22 MPG HIGHWAY BABEY. JUST GOT BACK FROM MY TRIP. MY HEADERS AND MY NEW SPARK PLUGS DID IT. THAT RENIX ECU IS A BEAST. IT WAS GETTING 17 MPG LAST NIGHT, BUT I GUESS THE COMPUTER KEPT LEARNING MY NEW SETUP. I THINK I'M GETTING AROUND 16 IN THE CITY. AND THAT'S WITH 4.5" LIFT AND 31X10.5 TIRES.
THE HULK IS BAAAAACK. AAAAARRRR!!!!
(btw, i don't care if people get mad about all capital letter post. i'm waay too happy to care)

 

yessss, verrry true. nothing wrong with a 4 banger, just think of it this way, is a huge, monsterous gas sipping beast

 

year: 2001
mileage: about 15-16 avg
tire size: 31's
driving style: slow since i put on 31s
aftermarket: 3in lift etc
city/highway ratio: idk/20

 

x2 what everyone said about the odometer being off for the larger tires. If you have stock gears and larger tires you will get worse city mpg, since the engine is working harder to move the tires, and better highway mpg since you can run higher speeds at lower RPMs. Thats if you aren't lugging the engine.

I have a 2000 XJ 4.0L, NP231, Auto, 96K miles. 235/75/R16 tires which are about 30"...more like 29.8". 2.5" exhaust with highflow cat and flowmaster super 40. I also have an Amsoil EA air filter that fits in the stock air box. I get 15-16 city and 19ish highway. When I put in the Amsoil filter I noticed a 1 mpg increase. A big factor with XJs and mpg is ethanol in the gasoline. In CT most stations have 10% ethanol in the gas which can result in up to a 15% decrease in mileage. When driving back from Maine I filled up with non-ethanol gas and got 22.5 mpg on the freeway, the highest I've ever gotten.

Running Marvel Mystery Oil in the gas tank every so often has helped me as well as some of my friends get better mpg, especially in winter. I have new spark plugs (champion coppers) also, but haven't put them in yet, hopefully I'll see an increase after installing them.

Those of you with larger tires might want to leave the tranny (auto) in 3rd gear on hills. The engine will rev higher but have to work less. It gets the best mpg around 2,000 RPM at highway speeds. I've found that leaving it in 3rd on a hill going 50-55 mph makes a difference instead of lugging it in overdrive.

Those of you getting 9-13 mpg might want to look into replacing your O2 sensors. They can get lazy over time and make the engine run richer without throwing a code. My friend with an '01 Ford Ranger 3.0L 4x4 saw a 2 mpg increase city and highway from running synthetic motor oil and diff fluids. Not saying it will work for everyone, since after all it is a Ford.

*All above mpg calculations are based off data recorded over a 2-3 month time period.

 

there is a better method you fill you tank and drive to see how much you burn and how far you went i don't know the exact method something like that

 

2ooo
4.o stock
275/15
about 16-18 in warm weather
in cold its about 10-11

 

i have stock lift and 235/75r15 tires and i get around 16/23 i'm hoping not to see a MAJOR decrease with my 4.5" and 31s about to be put on

 

You mean, like my ragdoll cat - she thinks, she is -, minus the gasoline (I haven't caught her with any yet)

 

Thanks, but i know how to figure it. With stock tires i got 240m a tank, with 31s i got 210m a tank, with 33s i get 170m. all with stock 3.55 gears. Do you really think my gas milage is getting that much worse because of the bigger tires? not exactly. i go further per axle rotation via larger tire. so my od/speedo read 50mph when i am actually going 60mph.

My point was that people are listing off mpgs and actually have no idea unless they have an od on there gps, or drive real far and use mile markers

 

Absolutely factory stock, 99 Cherokee, 4.0 liter 6 cyl auto Selectrac.
Since replacing the engine (due to bad bearings poor maintenance) and replacing all fluids and oils with fresh stuff. Synthetic oil in engine only
Over 3000 miles of combined driving--all on the road- 18.5 mpg. Highest tank was a little over 20 mpg.