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Gas mileage for 33's good or bad

S

snowjeep

NAXJA Forum User
Location
Buffalo,NY
I have a 2000 sport with Firestone m/t 33x12.5x15 on 15x8 light weight aluminiun rims. 4.10 gears, hp dana 30 and 8.25 chrysler in rear. No lockers or posi yet. 4.5 inches of lift. No winch or tire carrier not even a spare. My friend and I took a 250 mile trip with 95% being the thruway and got 14.2 mpg. Spedo has been corrected and motor has 89,000 miles. Running amsoil and large napa gold filter, K&N fipk, plugs have about 15,000 miles on them. It runs good just seemed low mpg. Never did a fuel filter. Anything I should look at or change?
 
How old are your O2 sensors? Don't feel too bad, I'm on 3.55's, 31's and lots of armor, I average 14.6. I really need new sensors.

4.10's aren't the best for 33's I guess... The tires are still pretty steep for that setup.

I know at least 2 guys running 33's, 4.56's with a manual, and they get an awesome 18 average.
 
I had 33s on my last heep. It was a 5 speed, so that helped.
I ran 3.07s for a while and got around 12mpg, then I went up to 3.55 when I swapped the axles and didn't notice a change in mileage.
Now I have 5.13s on 36s with an automatic and my mileage can't be more than 9 or 10mpg.
 
33s and 35s (at separate times of course) on 3.50 gears and a 5sp, 5000lbs of fun: 14 city, 18-20 highway. Lower gears in the axles do not automatically mean more mileage - but 14 highway does seem a little low. Changing the fuel filters certainly won't hurt anything...
 
damn Im running 35" SSR's and 5.13's and i seem to be pulling about 17!
 
I had essentially the same setup. 33's on 4.10's I was getting about the same mileage. Now I have about 8in lift, 33's and 4.56's my mileage went up to about 18-19mpgs on the hwy, 14-16 around town. I played around changing out sensors and don't think that made a big difference IMO
 
Now the real question, did any of you change the speedo gear accordingly for your tire size/gears?

With my lift, after calculating out the speedo difference, I get around 14-15mpg mostly city and 12-13 with a heavy foot.

~Scott
 
Thanks everyone just wanted to make sure I wasnt missing something on maiintaining my toy. But I forgot to add I had not front drive shaft because my buddy was putting joints in it for me. So I thought that would even make it better?
 
Not having a front ds wouldn't make a big enough difference. It's only spinning, and not driving, so the drag is minimal.

I'd make sure your O2 sensors are good, and check that your plugs, and TB are clean.
 
Fuel mileage isn't only related to motor tune or tire size. A lot of factors at play.

Biggest variable: How do you drive? Not joking or making fun of you.
you trip was 95% highway? How fast is that? You started out with a brick, lifted it, added big tires,.. Now you have a TALL brick. Aerodynamic drag increases at the square of speed, so a small increase in speed requires a large input of power.

My Jeep(mostly stock) gets around 19 highway, when cruising at 65-70.
I can also get 19 mpg lazing along at 45-50,... while towing a 1400lb trailer. Without the trailer, it almost 22.
 
I'm on 32s, 3.55s auto and I get about 15 on the highway. I've been debating going with 4.10s because I'm thinking of putting 31s on for the street and I know 4.56s will scream on the highway. Plus when I calculated it out, 4.10s with 32s will actually return my Jeep back to its factory settings. I'd love to get my mpg back, when I was on 235s I got about 18-20.
 
codyyy said:
I'm on 32s, 3.55s auto and I get about 15 on the highway. I've been debating going with 4.10s because I'm thinking of putting 31s on for the street and I know 4.56s will scream on the highway. Plus when I calculated it out, 4.10s with 32s will actually return my Jeep back to its factory settings. I'd love to get my mpg back, when I was on 235s I got about 18-20.
Click to expand...

i have the same set up.. ..and want to re-gear.
by scream, you mean the 4.56s will keep the rpms high at highway speeds?
for me on 32s with 3.55s and no intention of getting bigger tires, i want to do gears.
4.10s or 4.56s?

i do drive highway from vancouver to seattle a few times a month.
other than that, as my DD, it sees mostly city driving.

so, no on 4.56s because of the highway issue?
what is the highway issue?
 
kndrewa said:
...,so, no on 4.56s because of the highway issue?
what is the highway issue?
Click to expand...
'Motor would be turning about 11% faster to maintain the same speed using 4.56 gears over 4.10s. Above a certain point, you'd be wasting gas just to turn the motor faster. 4.10s on 32s is what the old TJ Rubicon had from the factory.
 
I have 32x11.50's MTR's on 15x8's. The heep is a 95 manual trans, 3.07, 4.0l with 145,xxx miles and Ive gotten 18.0-18.9 many a time on CITY/highway driving?
 
tbburg said:
'Motor would be turning about 11% faster to maintain the same speed using 4.56 gears over 4.10s. Above a certain point, you'd be wasting gas just to turn the motor faster. 4.10s on 31s is what the old TJ Rubicon had from the factory.
Click to expand...

FIFY.

I only use gear calculators as a guide, as there are so many other factors to take into consideration when you have bigger tires...

More weight
More rolling resistance
More wind resistance

For instance, even though 4.56s would put you back to "factory gearing" with 35s, I find 4.88s to be much better suited to it due to the factors mentioned above.
 
Ya, I know about the factors in selection gears, But he did ask what the highway issue was. The only issue with low gears on the highway is higher engine speed. I agree with you about the gears. Buddy of mine had a TJ with 4.88s and 35"s He liked it,... except for the highway. The only time that bothere him was when he went on thousand mile road trips. On the trail is was great!
 
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