Scan gauge bigger tires MPG accuracy

I just picked up a scan gauge from Amazon. I have been wondering if the scan gauge accounts for the bigger tires in the mpg calculation when you adjust for speed, or if it's just goes off of the odometer which is inaccurate. I went from the stock 215's to 31's so its like a 14% difference.

 

bump

 

yes, the speed adjustment is essentially compensating for the larger tires. If you calibrate with a gps til it reads the right speed on the freeway, it'll be accurate within a couple percent on mpg's, distance, and speed.

 

Correct me if I'm wrong guys but I think the scangauge is calibrated by running a tank thru it and punching some info in on the next fill up.

 

Thats for the fuel trim on it. You first need to get the speed correct if you have tires that are a non-factory size. Then when that is correct, do the fill up calibration on the fuel trim until the numbers match

 

What is the best way of getting the speed correct?

 

http://www.hypertech-inc.com/products-speedometer-calibrator.aspx

 

Hmmm... I got the Scan Guage II to fix the speedo issues (and other reasons) due to the bigger tires. lol. I wonder what I will need next if I were to order this?

 

That will handle bigger tires and re-gearing.

 

Re-gearing? Uh oh... Say what?

 

For an FJ, but just an example: