[Jackpine]

Originally Posted by p40whk

I've always been in the habit of checking my mileage whenever I fill up my tank and just got my Gryphon programmer a couple of weeks ago and am using the average and instant economy screens. I have noticed that the average economy for my Gryphon reads almost 2 MPG higher than what I actually get by dividing total gallons used by miles driven. I've run

I don't have any custom tunes yet so I'm running the canned 87 tow tune since I have an AFE CAI. My truck originally came with 235/70-17 tires and I just replaced them with 255/65-17 which is an option OEM size.

I am wondering if I need to set the tire size in my Gryphon or if my odometer is not displaying correctly. I've run 4 tanks though the truck and the results are pretty consistent.

Any suggestions?

Those tires are almost identical in terms of circumference, so I doubt you're going to see much effect by changing the tire size. Your old tires were about 2317mm around (subtracting 3% for squish) and the new ones are 2324mm at the same squish. That gives you only two revolutions less per mile. However, I WOULD use the Custom Options menu and set this new figure in anyway.

Before you do, please take the time to read my Q & A on the Custom Options menu so you won't be confused by the numbers you will see for Tire Size and maybe Gear Ratio. Make sure both values are entered correctly.

Now, back to the difference between the Gryphon and a hand calculation. I actually get about the same results as you do. The Gryphon always reads higher than what I am actually getting. I don't bother to monitor the Avg Economy for that reason. If you do though, DO not reset it at each fillup. It takes about 100,000 seconds of operation to "level" out and that corresponds to several tanks of gas. So, it will always be VERY inaccurate just after a reset. You'll probably find that you tend to have a fairly consistent error, and you can just "mentally" adjust for it.

- Jack