App - Add Modifier for Tire Size / Revs per Mile?
 

So I do not have factory sized tires on my truck. I went from a 245/75/16 to a 255/85/16. Basically a 30.5" tire to a 33" tire. This changes the revolutions per mile significantly. I can account for the Speedo difference using my Ultra Gauge easily enough.

Want I'd LOVE is an Android app, or if Fuelly could do it, that I can input my ODO reading into and have a pre-defined Modifier.

For example: My factory tires were 686 revs per mile. My current tires are 629 revs per mile.

686 / 629 = 1.09

So if my ODO reading and gallons pumped showed 17MPGs I'd multiply that by 1.09 to discover my real MPGs was actually 18.53.

Anyone know of a way to make Fuelly do this for me? Or an app that I can add a modifier to?