The Stovebolt Site Forums The Shop Area General Truck Talk Speaking of fuel mileage...........

I'll bet this is more than anyone wants to read but...I checked things 3 different ways. Note the tires and rear end below.

First, I went past a neighborhood radar sign.
Speedo=15. Radar=18. Actual speed is 20% higher than speedo says.
Speedo=30. Radar=35. Actual speed is 17% higher.
Speedo=39. Radar=45. Actual speed is 15% higher.

Second, I timed how fast I went through a highway mile check.
Speedo = 40 MPH. 74.63 sec for the mile = 48 MPH. That's 20% higher than the speedo's 40 MPH.

Last, I calibrated the odometer at a highway mile check. 1 mile on the highway changed the odo 1.19 miles.

So, I'm saying I'm off by about 20%. I multiply the odo reading by 1.2 for figuring MPG. I keep in mind the discrepancies in speed, especially at the school zones.