Bigger tires and lift affecting MPG...

[nfac556]

I just got a 2005 CRD and wanted to put a 2.5" lift and run 255/75/17's on it, but i wanted to know how how this would effect my MPG. Can anyone out there with a lift and 32's tell me what they're getting in town?

Thanks!

 

[tommudd]

Depends on if you're going to regear or not with 32s
plus with only a 2.5 inch lift will be tight
and yes even with your CRD it makes a difference if you regear or not
245-75-16s would work best on yours

 

[osufans]

On my gasser, I have the OME lift with a bit of a clevis lift as well, and am running 265/75R16's. I haven't had to trim yet, but the tires rub the swaybar, and I also get some rubbing on the pinch weld plastic cover. Nothing too drastic yet.

As far as MPG, I easily lost about 2 MPG average just doing tires. I don't recall what I got before doing the lift, but after the lift, I was only getting about 18MPG average with mostly highway driving. Now I get about 16. That's with 3.73 gears.

 

[tommudd]

I get 21 plus on the highway at 70-75 with a gasser and proper gearing :shrug::happy175:
Drops to 18-18.5 pulling my loaded trailer

 

[osufans]

I get 21 plus on the highway at 70-75 with a gasser and proper gearing :shrug::happy175:
Drops to 18-18.5 pulling my loaded trailer

Apparently you missed my comment about only getting 17-18 BEFORE the tires. :shrug:

I'd have to see it believe it, before I'd trust that you're really getting 21+ highway. Our '05 T&C 3.8 wouldn't do better than 22-23 highway at 70-75...and that was on long trips for vacation and such. It's quite a bit more aerodynamic than a lifted Jeep with 32" tires hanging out each side.

My Ranger that had 4.10 gears wouldn't get better than 16-18MPG highway either, with 32" tires, 5-speed auto, and the 4.0L OHV.

 

[tommudd]

Any time you want to go for a long ride I'll show you
Plus no way you can compare a Ranger to a KJ
Also ask Troy ( tjkj) same results with his and many others when geared correctly
I go from Toledo area to down home ( Marietta Ohio area) every two three weeks so nice 250 mile plus ride so I know what my average is

 

[osufans]

Any time you want to go for a long ride I'll show you
Plus no way you can compare a Ranger to a KJ
Also ask Troy ( tjkj) same results with his and many others when geared correctly
I go from Toledo area to down home ( Marietta Ohio area) every two three weeks so nice 250 mile plus ride so I know what my average is

Would you happen to recall what your MPG was before you lifted and such?

It appears there's quite a variance in MPG between Liberty's here...maybe some just get better than others from the get-go?

Like I said, mine from when I first got it, immediately after new plugs, oil, fluids, etc, and before I even lifted or put on tires, only averaged about 18-19. I don't recall if I ever purely tested highway, but most of my commute is highway anyways.

Not trying to sound condescending...I just have a hard time believing a 4600# flat-nosed Jeep with 32's and 4.10's can get 21+ highway.

 

[Ry' N Jen]

Hey, our rig also a gasser gets 22-23 mpg freeway after re-gearing!
Hell one time I got 24 mpg on a level roadway in Oregon State.
Not down any hill or high winds pushing the back of our KJ either!

Re-gearing is your Liberty's friend when you have 245-75-16's and bigger.
Regardless of what people claim that "It's just fine with 3:73's.:happy175:

 

[osufans]

Hey, our rig also a gasser gets 22-23 mpg freeway after re-gearing!
Hell one time I got 24 mpg on a level roadway in Oregon State.
Not down any hill or high winds pushing the back of our KJ either!

Re-gearing is your Liberty's friend when you have 245-75-16's and bigger.
Regardless of what people claim that "It's just fine with 3:73's.:happy175:

Again...what was your MPG before you ever lifted? I guess what I'm getting at is, is it possible that your Jeep got substantially better than average MPG before you even lifted? I've seen some people claim they're pulling in the neighborhood of 24 MPG stock. Mine has never gotten over 20 stock, so I wouldn't expect to get over 20 even re-gearing.

Also, back to my point about leaving my gearing at 3.73's...my Jeep is lucky to see 1K-2K miles in one year. It just doesn't make sense to drop over a grand re-gearing for no more than it gets driven. I never argued that re-gearing wasn't beneficial...just that it's not required. And I'll still stand by that argument. I don't even have a problem towing a small trailer with a 700# zero turn mower on it with stock gears...let alone just driving it by itself.

If we want to drag this post back to that argument, I'll kindly point out that some of you want to give a blanket answer for all situations and circumstances. There is no such validation for that argument...other than because you say so. You take no consideration of the specifics of each person's needs or the variables in the equation, yet claim to have the end-all be-all answer for everyone. That is why I give you guys grief over it. I don't mind the SUGGESTIONS...but it's when you tell me it's your way or the highway, that's when I get chafed and make a stink. I truly appreciate everyone's opinion and offers of input based on their experiences...but it just bothers me that some people ignore the input from others, and pretend their opinions are the only ones that matter.

So to prevent any further distraction from the original topic, I'll leave it at that.

Back to the OP...anytime you add mass (heavier tires, custom bumper) increased rolling resistance (again, heavier tires) or raise a vehicle thereby increasing drag, you will lose MPG's. As suggested, re-gearing can help you overcome power loss, but I wouldn't expect to see a huge improvement in MPG's because of it. Especially since going to a shorter gear (4.10 vs 3.73) usually equates to higher RPM's at highway speeds, which equates to more fuel being burned.

 

[rockymountain]

Especially since going to a shorter gear (4.10 vs 3.73) usually equates to higher RPM's at highway speeds, which equates to more fuel being burned.

That is totally false. regearing allows the engine to run in its most efficient power band (the main point of regearing). It also makes it easier for the engine to turn the bigger tires, thus using less fuel. Just because you are turning higher rpms does not mean you are burning more fuel.

 

[tjkj2002]

Again...what was your MPG before you ever lifted? I guess what I'm getting at is, is it possible that your Jeep got substantially better than average MPG before you even lifted? I've seen some people claim they're pulling in the neighborhood of 24 MPG stock. Mine has never gotten over 20 stock, so I wouldn't expect to get over 20 even re-gearing.

Also, back to my point about leaving my gearing at 3.73's...my Jeep is lucky to see 1K-2K miles in one year. It just doesn't make sense to drop over a grand re-gearing for no more than it gets driven. I never argued that re-gearing wasn't beneficial...just that it's not required. And I'll still stand by that argument. I don't even have a problem towing a small trailer with a 700# zero turn mower on it with stock gears...let alone just driving it by itself.

If we want to drag this post back to that argument, I'll kindly point out that some of you want to give a blanket answer for all situations and circumstances. There is no such validation for that argument...other than because you say so. You take no consideration of the specifics of each person's needs or the variables in the equation, yet claim to have the end-all be-all answer for everyone. That is why I give you guys grief over it. I don't mind the SUGGESTIONS...but it's when you tell me it's your way or the highway, that's when I get chafed and make a stink. I truly appreciate everyone's opinion and offers of input based on their experiences...but it just bothers me that some people ignore the input from others, and pretend their opinions are the only ones that matter.

So to prevent any further distraction from the original topic, I'll leave it at that.

Back to the OP...anytime you add mass (heavier tires, custom bumper) increased rolling resistance (again, heavier tires) or raise a vehicle thereby increasing drag, you will lose MPG's. As suggested, re-gearing can help you overcome power loss, but I wouldn't expect to see a huge improvement in MPG's because of it. Especially since going to a shorter gear (4.10 vs 3.73) usually equates to higher RPM's at highway speeds, which equates to more fuel being burned.

When I went to 265/75's with 3.73's I was getting about 9-10mpg's city and if I was lucky with a strong tail wind I could get 16mpg's on the highway,after regearing to 4.10's and having the speedo corrected I could get 13-14mpg's city and just shy of 22mpg's on the highway(still have reciepts for the gas).I can not really tell you about stock mpg's as my KJ never had stock tires on it as I drove it off the lot with half worn 245/75 MT/R's then went to 225/75 MT/R's which I could get 23mpg's on the highway.

After putting your bigger tires on you need to gear lower to get the engine rpm's up back to the original(or closer to) the OE specs to be in the power band.Your not "increasing" engine rpm's your just getting them back to what they were when 100% stock.So all your actually overcoming is the increased drag and weight,not increasing rpm's at all.The 3.7 in a KJ is more of a high rpm engine,it does not make it's peak torque till like 4000rpm's so the closer you get to that the better your off,mpg and powerwise.Peak torque is when your engine is the most effiecient.

 

[osufans]

That is totally false. regearing allows the engine to run in its most efficient power band (the main point of regearing). It also makes it easier for the engine to turn the bigger tires, thus using less fuel. Just because you are turning higher rpms does not mean you are burning more fuel.

I wouldn't say "totally" false. If all other equipment was left unchanged, shorter gears would equate to higher RPM's, equaling more fuel burned.

In the case of regearing to put the motor back into the power band due to changing tire sizes, I would maybe agree with you. However, you still have more rotating mass and most likely more rolling resistance and drag compared to a stock vehicle...so your MPG's should never exceed that of a stock vehicle. Even when properly regeared, it would be like you have a couple hundred pounds of extra weight to carry around versus the stock Jeep.

Now, I'm only saying this with the consideration that the stock Jeep is properly configured to be at optimum performance and operation. If the factory setup is somehow deficient in these things, there is a chance that even with bigger tires, regearing puts your Jeep in a configuration that allows it to perform better.

 

[osufans]

When I went to 265/75's with 3.73's I was getting about 9-10mpg's city and if I was lucky with a strong tail wind I could get 16mpg's on the highway,after regearing to 4.10's and having the speedo corrected I could get 13-14mpg's city and just shy of 22mpg's on the highway(still have reciepts for the gas).I can not really tell you about stock mpg's as my KJ never had stock tires on it as I drove it off the lot with half worn 245/75 MT/R's then went to 225/75 MT/R's which I could get 23mpg's on the highway.

After putting your bigger tires on you need to gear lower to get the engine rpm's up back to the original(or closer to) the OE specs to be in the power band.Your not "increasing" engine rpm's your just getting them back to what they were when 100% stock.So all your actually overcoming is the increased drag and weight,not increasing rpm's at all.The 3.7 in a KJ is more of a high rpm engine,it does not make it's peak torque till like 4000rpm's so the closer you get to that the better your off,mpg and powerwise.Peak torque is when your engine is the most effiecient.

I totally agree and understand what you're saying, that regearing essentially overcomes the larger tire circumference and puts the engine RPM's back to original. And by comparison...I'm getting 16 MPG combined right now, so I'm not complaining. I'm just curious how folks with 4.10s and 265's are getting better MPG than I ever did stock.

Referring back to my previous post...if the stock Jeep was properly configured from the factory, I couldn't see any possible way that regearing with bigger tires would allow you to improve your MPG's over that of the factory ratings.

However, if for some reason the factory configuration was just a tad too tall, making the engine work a little harder than it does after tires and regearing, then I can see how it could improve.

That's why I was asking what everyone got stock, just trying to compare apples to apples, since my previous best was only like 19MPG.

 

[rockymountain]

I got 18 stock.

The title of this thread is "bigger tires and lift effecting mpg".

It looks as though highway mileage is what they're seeing increase.

 

[tommudd]

Hiway and also in town I get better if I stay off the go pedal from light to light
Just got back yesterday from a 550 mile trip down home. Running in rain, 2 large long construction areas etc still managed 20.7 , averaged on the way down and back. I fill up when I leave from here, then right before I leave down there, then as soon as I get home . So have a real good indication of what I use
My sweetspot seems to be right about 70-73, at say 60-63 it wants to lug some but thats where it runs the best and at the right RPM
Total for the last 2 weekends was 1640 miles from Northwest Ohio over through PA to Butler and the Jeep Event, on over to Takoma Park maryland, back home then down to SouthEast Ohio and back so have a real good read on my mileage overall

 

[rockymountain]

And I'll add that even with the OD off I get the exact same mileage. I tested over 2 weeks driving with the OD off. I never forgot to hit the button when I took off driving. The mileage didn't change one bit.

Just because the engine is running slower doesn't mean it is using less fuel. OD in my KJ is worthless in town, I just get sick of hitting that stupid button.

 

[LetFreedomRing]

Just curious if you guys have any ethanol in your fuel. Also you have to take into account that some people live in flat areas compared to hilly areas. I for one live in a hilly area with 10% ethanol in our fuel. I average about 16-18 for city/mixed driving and 20.5 on the highway traveling about 75. Although having a 5 speed might help. :shrug:

 

[tjkj2002]

I totally agree and understand what you're saying, that regearing essentially overcomes the larger tire circumference and puts the engine RPM's back to original. And by comparison...I'm getting 16 MPG combined right now, so I'm not complaining. I'm just curious how folks with 4.10s and 265's are getting better MPG than I ever did stock.

Referring back to my previous post...if the stock Jeep was properly configured from the factory, I couldn't see any possible way that regearing with bigger tires would allow you to improve your MPG's over that of the factory ratings.

However, if for some reason the factory configuration was just a tad too tall, making the engine work a little harder than it does after tires and regearing, then I can see how it could improve.

That's why I was asking what everyone got stock, just trying to compare apples to apples, since my previous best was only like 19MPG.

How you drive,where you live(altitude,weather,and all that),fuel quality,and how you maintain your Jeep all take into account what mpg's your getting.Gotta figure also the different trans in KJ's.A KJ with a 42RLE will get just a little better mpg's then a KJ with a 45RFE due to gearing and weight difference between the trans(42RLE is far lighter).

When I was as close to stock as possible I could get 23mpg's highway,but that was at 2300' elavation and totally flat.Now with my SFA swap here in CO I'm lucky to get 16-17mpg's highway but when I went to KY and closer to sea level I was getting 18-19mpg's.

 

[tommudd]

Just curious if you guys have any ethanol in your fuel. Also you have to take into account that some people live in flat areas compared to hilly areas. I for one live in a hilly area with 10% ethanol in our fuel. I average about 16-18 for city/mixed driving and 20.5 on the highway traveling about 75. Although having a 5 speed might help. :shrug:

I drive all over, up here in the Northwest part of Ohio its pretty flat, but down home in Southeast Ohio its a lot of hills all you do is go up and down. recent trip was from Toledo area to butler Pa, down through Breezewood, over to Takoma Park Maryland and back so a mix of a little of everything

 

[yellocoyote]

I didn't gain any MPG's when I re-geared, but it may have something to do with the different transmission in my KJ. Not sure - I'm not all that good with gear ratio vs mileage. Illinois is pretty flat overall, and there's always 10% ethanol in the fuel. I did 16-18 city/20-21 highway before.... still doing that now. No change in tire size (yet)... but going to 265/75's in the fall, so we'll see how that plays out.