Sponsored

Upsized Tires and MPG Drop

BostonGuy

Outer Banks
Well-Known Member
Joined
Feb 10, 2021
Threads
40
Messages
198
Reaction score
271
Location
Boston
Vehicle(s)
Jetta
Your Bronco Model
Outer Banks
Clubs
 
Comment and Question.

I've got the 4dr non-sas OBX, went from stock tires to 275/70/18 General Grabber ATX. My MPG dropped by almost 2 (1.8). 10% seemed like a big drop.

In a perfect world do I need to use forescan or have my dealer "update" to car so it knows the tires are bigger? I'm assuming the bigger tires have better MPG then the computer is guessing.
Sponsored

 

HBTFD

Black Diamond
Well-Known Member
Base Sponsor (Level 1)
Joined
Mar 22, 2021
Threads
50
Messages
2,328
Reaction score
5,150
Location
Newnan GA
Vehicle(s)
F350
Your Bronco Model
Black Diamond
Clubs
 
If the tires have a larger circumference you are correct.
 

ProdigyJKU

Black Diamond
Well-Known Member
First Name
Rob
Joined
Jan 21, 2021
Threads
6
Messages
272
Reaction score
436
Location
Michigan
Vehicle(s)
2012 Wrangler
Your Bronco Model
Black Diamond
Part of it is that you speedometer is off. So now it thinks you only traveled 200 miles, when you've actually traveled 210 miles, throwing off the mpg calculations.

Other part it that the heavier tire mass and higher vehicle height making ot less aerodynamics.
 

pakrat

Badlands
Well-Known Member
First Name
JG
Joined
Jul 30, 2021
Threads
16
Messages
745
Reaction score
1,852
Location
Lake Tahoe
Vehicle(s)
Toyota 4Runner-F250-Tundra
Your Bronco Model
Badlands
Seems like a big drop regardless. I don't your engine size or gearing but there is a reason different packages get different gearing set-ups.

I've done similar on other vehicles and not seen that big a drop off on the computer or IRL when measuring via gps and at the pump. I'd be curious if you note a decently long trips mileage with google or something and manually calculate mileage at the fuel pump.
 
OP
OP

BostonGuy

Outer Banks
Well-Known Member
Joined
Feb 10, 2021
Threads
40
Messages
198
Reaction score
271
Location
Boston
Vehicle(s)
Jetta
Your Bronco Model
Outer Banks
Clubs
 
Seems like a big drop regardless. I don't your engine size or gearing but there is a reason different packages get different gearing set-ups.
I'm 2.3 with the standard gearing 3.73(?) I think. I'm mostly a mall crawler
 

Sponsored

Drex

Banned
Badlands
Banned
Banned
First Name
Jake
Joined
Jan 4, 2020
Threads
11
Messages
2,338
Reaction score
7,076
Location
various, construction engineer.
Vehicle(s)
'13 SLK55 AMG, '15 Indian Chief, '15 WRX
Your Bronco Model
Badlands
3.4% is error from larger diameter tire. The rest is added rolling resistance, air resistance from the wider tire, and a touch of weight increase. Actually it seems to me that you did better than I would have expected.
 

pakrat

Badlands
Well-Known Member
First Name
JG
Joined
Jul 30, 2021
Threads
16
Messages
745
Reaction score
1,852
Location
Lake Tahoe
Vehicle(s)
Toyota 4Runner-F250-Tundra
Your Bronco Model
Badlands
For perspective, I just finished a 1500 mile road trip. Sasquatch/2.7/4.7 gearing. 18.9 MPG on board computer, and 19.1 when I calculated it myself. 80-90% highway miles at speeds of 75-85 mph mostly. It stayed at an easy 1800-2200 rpms at those speeds and going up many mountain passes at altitude. The sasquatch gearing is perfect for 35" tires.

I'd run a manual calculation next time to go somewhere of any distance and keep track of those miles via google maps. I'm betting you don't suffer as much as you thought depending on your driving style.

If you don't think it feels like you lack power or the mileage isn't too much worse then have it calibrated and keep loving your Bronco. If you don't like the performance or the mileage has gone to crap because it has to select lower gears to keep up speed than you might think about re-gearing. I know that sucks but if you plan to have it for a long time and keep larger tires on it or even go bigger than you'll be glad you re-geared sooner than later. Better mileage and less stress on the drivetrain for the life of your Bronco. But do the manual fuel calcs first and ask yourself how it performs first and foremost.
Sponsored

 
 


Top