bigger tires= better mileage?

[mitsumotors]

i recently regeared my diff's to 4.56 gears and have been running 33" bfg m/t's. also... getting bad gas mileage(like 13mpg on highway). i drive very conservatively and try not to burn more gas than needed but this still seems low, i have done a major tune up and tried alot of different things to improve my mileage with no improvement. then i just seen this chart that shows what gears will give you what rpm's at highway speed with certain sized tires. is it possible that having 4.56 gears and 33" tires is a little overgeared and maybe if i ran a bigger tire(35") i would actually get better mileage. i do mostly highway driving and no hills, just flat ground.
thanks:wave:

 

[lancey3]

Not at all. 4.56 is pretty much perfect for 33s. Do a complete tune up.

 

[mitsumotors]

do you think the fact that i got new 2.25" exhuast from the manifold back with no cat and a high flow muffler but use a stock airbox and filter, will give bad gas mileage? i heard that its possible that if you upgrade your exhuast but have a crappy intake setup you will get worse gas mileage?

 

[emr1101]

id say try some 35s. see if you cant find a buddy to swap tires for a little bit for. do you know how to properly guage fuel economy? some people do it wrong..

 

[Mstrkage]

Is your speedometer correct?
As far as a bigger tire getting you better economy, there is a sort of sweet spot between larger tires and gear ratios and the weight of a larger tire. Plus a larger tire puts you just that much further into the air. I'm not saying a 35 wont help but I would doubt it.

 

[mitsumotors]

well, i just fill my tank, note the mileage, drive, fill up again, note the mileage and how much fuel i used then figure out how manny miles i get for each gallon of fuel used, but since i'm a little overgeared my speedo about 7% slow so then my odo is too so i take that into account. but also, my speedo goes up as i accelerate but when i let off it takes a while to come back down(its a little slow) so that probably means that my odo is not accurate either right?

 

[mitsumotors]

also someone on this forum said that if you don't correct your speedo, it will mess up your computers ability to properly read engine speed or something like that and could result in poor mileage.

 

[Darky]

Your odo and speedo aren't dead on with each other. What I mean is, with my 30" tires, my speedo is dead accurate. Its been verified by them little roadside "Your Speed Is:" signs as well as by GPS. However my odo, when compared against the milemarkers on the highway, is off. For every mile traveled, it only reads 0.8. So, I correct my mileage by:
Trip meter/0.8/gallons pumped=mpg
and get fairly accurate readings based on that. Find out what your odo is off by using milemarkers or some other known accurate mileage reading and then figure your mileage that way. I know if I don't correct, it looks like I'm only getting 14ish. I actually get around 18.

 

[Pharaoh XJ]

the stock setup for most 6 cyl auto is:
3.55 + 215s

to acheive that same ratio:
3,73 + 30"
4.10 + 33"
4.56 + 37" Yes I know

Theoretically Using these combos will bring the odometer back to stock. But that doesnt mean bringing back stock milage there are several other factors wind resistance, drag, rolling weight, etc

 

[Ray H]

And how much do those 33s weigh? And how much rolling resistance does a 12.5" wide tire have? And how tall is your XJ?

 

[mjma]

They might help. I have 4.88s and I run Q78 swampers (35.5" measure) and a set of 35x12.5r15 BFG ATs. Surprisingly, the swampers get me better mileage on the highway!! I think it's because they are a bit taller than the BFGs.

 

[winkosmosis]

What do you think gives you the right to pollute everyone's air by taking off your cat, just so you could gain a couple horsepower???? Seriously, I want to know your reasoning.

 

[cal]

bigger tires won't help, you have some other issue. When is the last time you cleaned your throttle body or replaced your o2 sensor?

 

[Darky]

What do you think gives you the right to pollute everyone's air by taking off your cat, just so you could gain a couple horsepower???? Seriously, I want to know your reasoning.

I was kinda thinkin along the same lines. Pull your cat, pollute more, give greenies another reason to demonize us...

 

[toysupra14]

Well I have some 33" BFG MT on steel wheels I also get around 13-14mpg...with my 4.56's. I swapped with a friend who had 35" buckshots with alum. wheels I got around 15-16.... so Idk if it was the wheels or the tire sizew but it did improve my mileage.

 

[planefixer]

I'm running 35" tires and 4.56 gears which keeps it within 3% of "stock" configuratuion.I get 15-17 mpg on average (as much as 20-21 mpg coming down out of the mountains ) and turn 2300 rpm @ 75 mph on level ground.A couple of years ago I ran my 35s with 3.55 gears for 1 1/2 months, until I had money to regear, and was getting around 23-25 mpg :laugh: (obviously no low end power).

 

[emr1101]

I was kinda thinkin along the same lines. Pull your cat, pollute more, give greenies another reason to demonize us...

You could just put on an aftermarket high flow cat? that would help out your power plus replace jeeps shitty, prone to failure stock catalytic convertors. Thats what ill probobly do, plus a header and a super 44...

 

[Mosephus]

I skimed the thread but didn't see it asked, Auto or manual?

 

[razdrvr]

I managed to get 18.65mpg hiway with 4.56 and 35 cruise set at 65 according to GPS.

 

[winkosmosis]

I'm running 35" tires and 4.56 gears which keeps it within 3% of "stock" configuratuion.I get 15-17 mpg on average (as much as 20-21 mpg coming down out of the mountains ) and turn 2300 rpm @ 75 mph on level ground.A couple of years ago I ran my 35s with 3.55 gears for 1 1/2 months, until I had money to regear, and was getting around 23-25 mpg :laugh: (obviously no low end power).

I don't understand why some people can get good mileage, and others very bad with the same config. You got 23-25mpg highway with 35s and stock gears, yet other people get 12mpg, and they say they don't drive with a heavy foot.