Speedometer calibrator and gas mileage?
Thread Starter
JK Newbie
Joined: Oct 2007
Posts: 17
Likes: 0
From: Overland park, KS
Speedometer calibrator and gas mileage?
Has anybody seen an increase in gas mileage after calibration of the speedometer?. I went from stock to 35's and my shift points on the highway are all over the place! The automatic tranny can't seem to settle in any one spot for any length of time. I've read the speedometer calibration unit will fix this, but I would feel a lot better about buying one if I thought I might get a "little" better gas mileage. I would think that by increasing tire diameter without calibration it would make the gas mileage "appear" to drop significantly. Thanks in advance
JK-Forum Founder
Joined: Jul 2006
Posts: 36,534
Likes: 16
From: Laguna Niguel, CA
Agreed - if you really want to get your MPG where it needs to be, you will need to regear. However, if you want your speedo and MPG computer to read correctly, you will need to have it recalibrated.
JK Super Freak
Joined: Sep 2007
Posts: 1,623
Likes: 5
From: Lawrenceville, NJ
Remember - if you DON'T recalibrate, AND don't remember that the numbers are wrong...you will THINK you have a giant loss in mpg.
Example:
The larger tires have fewer revolutions per mile...so, your speedometer says you are going 60 mph, but, you might be going 70 mph....which uses a lot more gas due to the aerodynamics of a brick, etc.
The Odometer says you went 300 miles, but, you might have gone 350 miles, etc.
In short, you drove faster than normal, and further than you thought...so, when you divided the miles you THOUGHT you drove by the gallons of gas used to do it, you got a lower mpg number than you WOULD HAVE, if, you had driven the same speed, and the actual distance.
IE: You drove faster, and went further, than you thought you did, because the larger tires make fewer revolutions per mile.
Add that to any advantages you could get from a better shift point, etc...and it looks a lot worse than it is without knowing/compensating for the new diameters.
Example:
The larger tires have fewer revolutions per mile...so, your speedometer says you are going 60 mph, but, you might be going 70 mph....which uses a lot more gas due to the aerodynamics of a brick, etc.
The Odometer says you went 300 miles, but, you might have gone 350 miles, etc.
In short, you drove faster than normal, and further than you thought...so, when you divided the miles you THOUGHT you drove by the gallons of gas used to do it, you got a lower mpg number than you WOULD HAVE, if, you had driven the same speed, and the actual distance.
IE: You drove faster, and went further, than you thought you did, because the larger tires make fewer revolutions per mile.
Add that to any advantages you could get from a better shift point, etc...and it looks a lot worse than it is without knowing/compensating for the new diameters.