Quantifying power and MPG loss from larger wheels/tires? - Jeep Wrangler Forum
Jeep Wrangler Forum

Go Back   Jeep Wrangler Forum > TJ Jeep Wrangler Forum > TJ General Discussion Forum

Join Wrangler Forum Today


Reply
 
Thread Tools

Please support our sponsors and let them know you heard about them on WranglerForum.com
Old 02-07-2011, 05:11 PM   #1
Jeeper
 
Join Date: Jan 2011
Posts: 44
Quantifying power and MPG loss from larger wheels/tires?

We're all aware that replacing our stockers with larger wheels and/or tires will reduce power and MPG, but is there a formula to determine how much?

I'm looking to upgrade, and I may or may not be willing to accept the consequences depending on what they are.

Details:

Jeep specs: 2004 TJ Sport, 4.0, 3speed auto with overdrive, stock 15" Ravines with stock 30x9.5 tires. DD (60/40 highway and town), very little to no offroad use. I occasionally pull a 5'x8' utility trailer.

New wheels/tires for consideration: 17" alloys (guessing ~13/lb per wheel gain) and 32" (actually 255-75-17) tires.

Anyone know how bad of a hit I would take or a way to make a rough guess? Am I losing 5hp? 50hp? 5MPG? 1MPG?

Thanks in advance.

AkshunJebus is offline   Quote Quick Reply
Old 02-07-2011, 06:46 PM   #2
Jeeper
 
Neil F.'s Avatar
 
Join Date: Nov 2007
Location: Marlton, NJ
Posts: 4,908
Images: 1
Do a search on MPG. There are plenty of threads for that subject. In them there are plenty of posts referencing tire size. The gears you have also play a role.

__________________
2003 TJ, 33" BFG AT, 2" BL, 2" BDS spring lift, Truck Lite headlights, Homemade sunrider top.
Neil F. is offline   Quote Quick Reply
Old 02-07-2011, 08:01 PM   #3
Jeeper
 
Tommy2Times's Avatar
 
Join Date: Jan 2011
Location: South Jersey
Posts: 356
I'm about 60% thru a full tank after going from stock "canyon" rims on 31x10.5's with the 3sp auto and 4.0L 6cyl. EXCEPT no OD. I track my mileage religiously. I seem to drive mine just about exactly as you do, but i'm 65/35 Around Town/Highway, even towing the same sized trailer once in a while. Lol. I'll let you know how my MPG dropped in a few days once I finish off this tank.
Tommy2Times is offline   Quote Quick Reply
Old 02-07-2011, 08:11 PM   #4
Jeeper
 
Join Date: Jan 2011
Posts: 44
Thanks Neil, but that's my point. I've done the searches, read the threads and they all bullet point to lost power and lost MPG. I'm looking for how dramatic of a change is it.

You did remind me that I didn't list my gearing though: 3.73.

Tommy, I would appreciate it! That's the kind of real-world info I'm looking for, although I'll probably do worse than you since I'm looking at the signicant weight gains of 17"s. Unless you wenty to steelies. That might be a somewhat resonable comparo.
AkshunJebus is offline   Quote Quick Reply
Old 02-07-2011, 08:25 PM   #5
Hardcore Jeeper
 
Peepers's Avatar
 
Join Date: Oct 2010
Location: Windsor, CT
Posts: 3,320
You don't actually lose power. Its still there. but you are using more of it to turn the tires, so it seems like you have lost power.
__________________
What have we got?
We have one heavily armed Recreational Vehicle


ΣΧ
The Power Tech 6
Peepers is offline   Quote Quick Reply
Old 02-07-2011, 08:34 PM   #6
Jeeper
 
Join Date: Apr 2008
Location: Mississippi Gulf Coast
Posts: 339
Send a message via AIM to CapnDean
It's called the ass dyno (as in dynamometer)

I cannot think of any way to describe it other than...... After a couple of years with 3.07 gears in my 99 TJ on 31's...I went up to 33's for a week and then BAM dropped in my 4.88's WHHHHOOOOOOOO WEEEEEE I got ass again!
__________________


1999 TJ Sport 4.0L I6 5 spd Warn 8000
4" susp 1" body 35" AT's
4.88 Gears in Ford 8.8
Adv Adapter SYE
Adam's Driveshaft
CapnDean is offline   Quote Quick Reply
Old 02-07-2011, 09:04 PM   #7
Jeeper
 
InfernoGirl's Avatar
 
Join Date: May 2009
Location: Newburgh IN
Posts: 11,419
Quote:
Originally Posted by Tommy2Times View Post
I'm about 60% thru a full tank after going from stock "canyon" rims on 31x10.5's with the 3sp auto and 4.0L 6cyl. EXCEPT no OD. I track my mileage religiously. I seem to drive mine just about exactly as you do, but i'm 65/35 Around Town/Highway, even towing the same sized trailer once in a while. Lol. I'll let you know how my MPG dropped in a few days once I finish off this tank.
Did you swap your speedo gear? If not your readings are not accurate, and your calculations will be off as well....

OP, does it really matter if you're getting 13mpgs vs. the 15 you got before? If so, don't do it. The optimal mpg for any vehicle will be in it's stock form, unless you spend a mint modding it....

No one can provide you with the answer you want because there are way too many variables to account for. Compiling all the data would be ridiculous. Every brand of tire weighs a different amount as do wheels... gears, how much after market weight are you carrying, etc.... You see where this is going.
__________________

Dirty Mudder column covers|

'01 Wrangler Sport, Sienna Pearl Mine
'07 Rubicon 2D, Flame Red His
'11 Wrangler Sport 4D, Black Ours...

Quote:
Originally Posted by Kate View Post
Not every girl, is a Jeep girl. We're a special breed.
InfernoGirl is offline   Quote Quick Reply
Old 02-07-2011, 09:27 PM   #8
Rock-Rubber

WF Supporting Member
 
GoldenSahara00's Avatar
 
Join Date: Aug 2010
Location: SCPA
Posts: 16,555
You should be pretty well off with that gearing and 33s. just take er easy on the peddle and youll be fine. the 3 speed autos deal with 33s best from what I have learned. I have a 3sp auto and plan on 33s in a month or two. Your MPG will take a hit, but big deal. if you wanted a CAR you shouldnt have bought a JEEP :P I havce accepted that my jeep never has or will get good mileage. buy a sunfire for long trips :P
__________________
Ryan - A good eye, a light foot, and a smart rig.
Bolt-ons are boring
AMERICAN JEEPER
My Build - http://www.wranglerforum.com/f118/pr...a00-74622.html
Rausch Creek Trip: 2014 Trip Coming Soon
GoldenSahara00 is offline   Quote Quick Reply
Old 02-08-2011, 01:53 PM   #9
Jeeper
 
Tommy2Times's Avatar
 
Join Date: Jan 2011
Location: South Jersey
Posts: 356
Quote:
Originally Posted by InfernoGirl View Post
Did you swap your speedo gear? If not your readings are not accurate, and your calculations will be off as well....

OP, does it really matter if you're getting 13mpgs vs. the 15 you got before? If so, don't do it. The optimal mpg for any vehicle will be in it's stock form, unless you spend a mint modding it....

No one can provide you with the answer you want because there are way too many variables to account for. Compiling all the data would be ridiculous. Every brand of tire weighs a different amount as do wheels... gears, how much after market weight are you carrying, etc.... You see where this is going.

Yes, My I swapped the speedo gear, surprisingly easy to do. I'm running nearly perfect mph now. I checked using my phone gps and tomtom gps. I Tested them both in the girlfriends Altima, they were dead on with her speedo, then over to the jeep. I'm off by about 1-2mph.
Tommy2Times is offline   Quote Quick Reply
Old 02-08-2011, 06:45 PM   #10
Jeeper
 
jgorm's Avatar
 
Join Date: May 2010
Location: San Diego
Posts: 1,831
Quote:
Originally Posted by InfernoGirl View Post
Did you swap your speedo gear? If not your readings are not accurate, and your calculations will be off as well....

OP, does it really matter if you're getting 13mpgs vs. the 15 you got before? If so, don't do it. The optimal mpg for any vehicle will be in it's stock form, unless you spend a mint modding it....

No one can provide you with the answer you want because there are way too many variables to account for. Compiling all the data would be ridiculous. Every brand of tire weighs a different amount as do wheels... gears, how much after market weight are you carrying, etc.... You see where this is going.
+1. Its hard to measure any loss, especially after you regear. I believe lots of the guys that state they lost mpg didn't factor in that their speedo is off. When I went from 31s to 33s I went from ~200mi / tank to 165mi / tank, but when I corrected for the difference it was very similar. If you don't regear, it will feel slow for sure. MPG might take a hit, especially if you drive fast, but it will be from the increased wind profile more than the small bit of inertia the new tire wheel setup will have.
jgorm is offline   Quote Quick Reply
Old 02-08-2011, 08:21 PM   #11
Jeeper
 
Join Date: Jan 2011
Posts: 44
Thanks for all the replies. I'm not really worried about losing 1 or 2 mpg... Heck my car only gets 16 mpg.

Ass dyno... lol.
AkshunJebus is offline   Quote Quick Reply
Old 02-08-2011, 08:39 PM   #12
Jeeper
 
Join Date: Jan 2010
Posts: 251
I am not sure how it works but the speedo is not the only thing you need to check. I had 225 75 15's (stock) on my 99 TJ auto. I went to a 235 75 15. My speedo is almost still perfect with a GPS. It is dead on until I hit about 55 mph. At 60 mph it is 2 mph off. However I drove 50 miles (GPS) and my odometer only showed 42 miles. So just because your speedo is accurate does not always mean that your odometer is still on. Get a GPS and check them both.
flyin-lowe is offline   Quote Quick Reply
Old 02-09-2011, 09:55 PM   #13
Jeeper
 
Tommy2Times's Avatar
 
Join Date: Jan 2011
Location: South Jersey
Posts: 356
Well I did a little extra driveing this week just to see what my new mpg are with the new bigger tires. I filled up tonight and went to my mpg app on the phone and almost made a mess in my pants when i saw the outcome! 14MPG!!!!!!!!!!!!! WHOOOOOHOOOO!!!!!!!!!! I know there are a lot of factors that affect mpg, but I've been getting 13-15 religiously, and was happy to see that it didn't change, I was truely expecting to see a single digit.!
Tommy2Times is offline   Quote Quick Reply
Old 02-09-2011, 10:32 PM   #14
Jeeper
 
InfernoGirl's Avatar
 
Join Date: May 2009
Location: Newburgh IN
Posts: 11,419
Quote:
Originally Posted by flyin-lowe View Post
I am not sure how it works but the speedo is not the only thing you need to check. I had 225 75 15's (stock) on my 99 TJ auto. I went to a 235 75 15. My speedo is almost still perfect with a GPS. It is dead on until I hit about 55 mph. At 60 mph it is 2 mph off. However I drove 50 miles (GPS) and my odometer only showed 42 miles. So just because your speedo is accurate does not always mean that your odometer is still on. Get a GPS and check them both.
Correcting the speedo to the appropriate toothed gear for the tire size also corrects the odo.


Edit: Tommy, the EVlC reading is not accurate. To get a good reading you have to do the math. EVIC is an average.
__________________

Dirty Mudder column covers|

'01 Wrangler Sport, Sienna Pearl Mine
'07 Rubicon 2D, Flame Red His
'11 Wrangler Sport 4D, Black Ours...

Quote:
Originally Posted by Kate View Post
Not every girl, is a Jeep girl. We're a special breed.
InfernoGirl is offline   Quote Quick Reply
Old 02-09-2011, 11:07 PM   #15
Jeeper
 
mum954's Avatar
 
Join Date: Dec 2010
Posts: 53
I thought this article was really helpful.

http://jeep.us41.org/wheels/

I think this is a common dilemma, mine's still bone stock but it would be pretty nice to be able to run 33s, 4" lift, get 30 MPG, and still beat a 3 series off the line. Hahaha
mum954 is offline   Quote Quick Reply
Old 02-10-2011, 09:18 AM   #16
Jeeper
 
Join Date: Jan 2011
Posts: 44
Thanks Tommy. I realize that's not concrete, but it's promising! Are you calculating MPG by doing the math on the fuel used over the miles driven? I'm confused by InfernoGirl's comment about the EVIC being an estimate. As far as I know all my Jeep tells has is an odometer and a trip... unless I haven't found the good stuff yet.

InfernoGirl, are you talking about the odometer isn't accurate because of the tire size? I'd buy that, but I wouldn't think it would be an "average". Is there a MPG button I'm missing some where on my Jeep? Could be, only had it a week or so.

Mum, great link. Thanks!
AkshunJebus is offline   Quote Quick Reply
Old 02-10-2011, 09:23 AM   #17
Jeeper
 
InfernoGirl's Avatar
 
Join Date: May 2009
Location: Newburgh IN
Posts: 11,419
Ahhh, nevermind.... Just now noticed this was in the TJ section. Your odo is off because of the tire size if you haven't upgraded the speedo gear. JK's have an electronic mpg thingy that isn't exactly accurate.... Sorry for the confusion.
__________________

Dirty Mudder column covers|

'01 Wrangler Sport, Sienna Pearl Mine
'07 Rubicon 2D, Flame Red His
'11 Wrangler Sport 4D, Black Ours...

Quote:
Originally Posted by Kate View Post
Not every girl, is a Jeep girl. We're a special breed.
InfernoGirl is offline   Quote Quick Reply
Old 02-10-2011, 12:27 PM   #18
Jeeper
 
Join Date: Dec 2010
Location: Traverse City MI
Posts: 47
Quote:
Originally Posted by jgorm View Post
+1. Its hard to measure any loss, especially after you regear. I believe lots of the guys that state they lost mpg didn't factor in that their speedo is off. When I went from 31s to 33s I went from ~200mi / tank to 165mi / tank, but when I corrected for the difference it was very similar. If you don't regear, it will feel slow for sure. MPG might take a hit, especially if you drive fast, but it will be from the increased wind profile more than the small bit of inertia the new tire wheel setup will have.


so, what is the correct tooth gear for 33" tires ?? I know mine is off and would like to buy a new gear. its a 4.0 tj 5 spd
prettyboytoys is offline   Quote Quick Reply
Old 02-10-2011, 12:46 PM   #19
Jeeper
 
Tommy2Times's Avatar
 
Join Date: Jan 2011
Location: South Jersey
Posts: 356
Yes, I have been doing the math off the ODO and fuel fill volume. I don't know how I could make it more accurate. :P
Tommy2Times is offline   Quote Quick Reply
Old 02-10-2011, 01:28 PM   #20
Jeeper
 
InfernoGirl's Avatar
 
Join Date: May 2009
Location: Newburgh IN
Posts: 11,419
Good deal!

__________________

Dirty Mudder column covers|

'01 Wrangler Sport, Sienna Pearl Mine
'07 Rubicon 2D, Flame Red His
'11 Wrangler Sport 4D, Black Ours...

Quote:
Originally Posted by Kate View Post
Not every girl, is a Jeep girl. We're a special breed.
InfernoGirl is offline   Quote Quick Reply
Reply

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Jeep Wrangler Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
If you do not want to register, fill this field only and the name will be used as user name for your post.
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Thread Tools

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



logo carid shop wrangler parts carid fender flares custom wheels store avs deflectors at carid
» Rates
Get low rates on auto insurance in Canada!

» Network Links
»Jeep Parts
» Featured Product

All times are GMT -5. The time now is 07:01 AM.



Jeep®, Wrangler, Liberty, Wagoneer, Cherokee, and Grand Cherokee are copyrighted and trademarked to Chrysler Motors LLC.
Wranglerforum.com is not in any way associated with the Chrysler Motors LLC