I have an auto with 3.73 gears, 2.5" of lift and 33's. Be;ieve it or not my Jeep has a fair amount of power and has no problem doing over 80 mph.

When my tires wear out I am thinking about moving up to 35's. I get around 14-15 mpg right now. How much worse will it get?

 

depends on your driving habits.

I get 9.8 all around with 35s.

just a guess probably around 1-2 mpg lower than what your getting now.

 

Re-gearing will help. I had 35's and 3.21 gears for about 2 months and got about 12 city and 15 highway. I upgraded to 4.88 gears and now get 14-15 city and 16-17 highway.

 

I have a two door , 4.10's and 35"s and get 13+ with my daily driving. Wind is a big factor for better mileage on the highway as a good tail wind will get me up to 20 mpg. Head wind and it drops to 12 mpg.

 

9.8!!! Why so low?

 

I can live with those numbers for a while, just not 9.8!

 

I don't think I would see 20mpg if you dropped me out of a plane!

 

I HAVE A 4 DOOR AUTO WITH 4:10'S AND 35'S I HIT CRUISE AROUND 65 EVERYDAY. I GET AN AVERAGE OF 17mpg. I ALSO HAVE A 48 MILE DRIVE TO WORK 1 WAY. AND MOST OF THE TIME DRIVING SOUTH I GET A HEAD WIND AND HAVE TO DRIVE WITH O/D OFF. I CAN GET ABOUT 380 MILES TO A TANK.

 

Good one!

 

Off hand WAG (wild ass guess) in the 12mpg range. Three things matter when you talk about MPG driving habits, driving habits, driving habits. Your tires are your final gear reduction..... the larger diameter of the tire the higher the gear.

After I geared to 5.13 I see +18mpg on the highway at 60 with 35s, lift, & lots of heavy metal upgrades. If I drove incorrectly that would drop.

Here is what the re-gear is about. An internal combustion engine is most efficient at its peak torque RPM range. When your gears are to high (numerically lower # R&P ratio) starting off the engine RPMs are to low and the motor is in a strain.

When you start off in a gear to high you rev the motor so it will not die and slip the drive train a lot (either from the clutch in a manual or the torque converter in an auto). Also, if your engine RPM is to high when cruising then you are also wasting fuel.

The best thing is to have as many gears as possible between stopped and max cruising speed so you keep the motor at the RPM it is most efficient. But who wants to shift a thousand times???

The next best thing is to place the set of gears in your existing transmission back into the motor speed/actual speed of the jeep correct range. So you do not strain your motor to get moving, so you can keep the motor as close to peak torque while accelerating, and have the motor at peak torque RPM while cruising. To do this the easiest and cheapest way is to replace your R&Ps. The trick is if you go to low you hurt your top end speed and efficiency