Like most others I am contemplating 35 in tires, but I'm on the fence with 33's. What is confusing me is everyone's claims of reduced gas mileage. I understand that they will be heavier but I currently have 32's and with my normal commute (20 miles each way). I travel on a highway @ 65 mph. I generally tach around 2900 rpm. And average 19 mpg weekly. With the larger tires wouldn't that allow me to travel at 65 mph at a lower rpm resulting in better mpg? (4dr JK I think 3.73 gears with an AT and running the flashpaq 87 tune. 1 or 2 mpg isn't going to break me but I am hoping you folks can help me out with some clarification.

 

They're not just heavier, they're wider, with more surface area meeting the road (ie friction).

I'm running stock Rubi 4.10 gears + superchips 87 tune + 35 km2 and at 65mph my rpms produce barely enough to stay in overdrive on my automatic transmission. If I don't kick out of OD on the highway I can still get 19-21 mpg. However, if there's even the slightest hill, head wind, or even if I barely accelerate, it kicks out of OD, sending the rpms super high. That totally kills my highway mpg when it happens. And now that the speed limit here just got bumped to 70, I'm rarely in OD. So that's while I'll end up regearing... To raise my rpms to where the engine is in its powerband. Running an hour at 2500rpms should save mpg vs constantly switching between 1800rpms and 3500rpms.

 

Forgot to add that I was on the fence between 33s and 35s, leaning towards 33s for the mpgs, until I did three or four trips with my local Jeep club.

After that, I wanted 35s regardless of the mpg. But my roundtrip work commute is only 10 miles, so I'm somewhat lucky.

 

Gas mileage will suffer with 35's...I get around 12 or 13 back and forth to work.

 

I have 35's with 3:73 gears and a Superchips Flashpaq. I get between 15 and 18 mpg on the hwy. and between 12 and 14 city. But, Ive learned to keep my foot out of it.

 

do the 35s and save for a re-gear. you can still get 16mpg+.... or dont re gear but either way do the 35s

 

I really dont know what i am doing wrong, according to my math i am only getting 13-14 mpg and thats with a 08 unlimited rubi w stock 4.10's and 32's, and not sure if its been flashed (i am the second owner) but it seems to be more responsive then the ones i test drove at the dealer. But milage really sucks, but I did take a road trip last week and got 17 mpg on the highway. but everyone keeps talking about getting anywhere from 16-24 mpg.

 

Yeah your doing something wrong...
I get about 14 mpg with 4.10 gears and 37x13.50 Toyo M/Ts.

 

Agreed... I am getting 13 mpg with 5.13 and 35s... and most of that poor MPG is due to me being geared too low for a 6-speed on 35s...

 

With 32's, why are you OD Off? I don't know the terrain out there, but with 3.73's and 32's, you shouldn't be having trouble holding 65.

For mpg comparisons, there are too many variables involved. In general - Plan on your mpg's going down with the 35's. And plan on them coming back up a bit when you recalibrate to get accurate numbers. And plan on them coming up a bit more when you regear.

But yes, you are correct that going to taller tires will bring your rpm's down and should improve your mpg's.




I don't do a lot of freeway, but on a recent 60+ mile trip I got 21.1 mpg.
Sounds good, huh?
Sounds even better when you look at the specs:
Auto. 35's. Fairly heavy 4door w/bumper and winch, hardtop, lots of gear in back. At altitude in Colorado, so LOTS of hills and elevation changes.

Lots of bone stock manuals, down at sea level, aren't even posting that mpg.

What were the particulars that helped me out?
5.38's. Flashpaq tow tune. 70mph max, instead of trying to stay with the traffic at 75-80. Dash gauge instead of hand calc'd. My destination was about 800ft lower than where I started. (I got 17.5mpg on the way back)

So again, there are too many variables involved for you to base your mpg's off of anyone else's mpgs. You can only make some semi-educated guesses based on the information given.