Y'all - I know this has come up in a couple of threads, but I found this article interesting on how much error could be in the odometer / MPG calculator. Just thought it interesting enough to share.

The staff of Diesel Power has now spent considerable time behind the wheel of four ’11 Ford Super Duty’s, and we’re noticing a pattern…





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On three of the four trucks (the fourth truck may have the problem, too, I just can’t recall) we’ve conducted mileage testing on, the odometer’s are off by 1 to 4.9 percent. The odometer’s read low, and the discrepancy between actual miles traveled and the odometers widens as speed increases. We’re told that many of the Ford’s odometer’s may have been calibrated wrong from the factory. If you own an ’11 you owe it to yourself to validate your odometer’s accuracy. You may find that your truck gets up to 5% better mileage than it’s leading you to believe.

Example 1:
Trip: Cross country road trip (Michigan - Colorado)
Model: ’11 Ford F-350, four-wheel drive, XLT, crew cab, 3:73 gears, DRW
Tires/Wheels: 245/75R17
Speed: 65-66 mph
Error Test: From mile-marker 167 to 67 (100 miles traveled), odometer read 96.4 miles traveled
Error: 3.6% (chart above, courtesy of Harry Rawlins)
Error’s Effect on Mileage: 16.3 mpg (truck) Vs. 16.9 mpg (actual)

Example 2:
Trip: Cross country road trip (Michigan - Colorado)
Model: ’11 Ford F-350, four-wheel drive, XLT, crew cab, 3:73 gears, DRW
Tires/Wheels: 245/75R17
Speed: 75-76 mph
Error Test: From mile-marker 132 to 32 (100 miles traveled), odometer read 95.1 miles traveled
Error: 4.9%
Error’s Effect on Mileage: 15.0 mpg (truck) Vs. 15.8 mpg (actual)

Example 3 (Project 6.7L Power Stroke):
Trip: Two, 10-mile runs up Interstate
Model: ’11 Ford F-350, four-wheel drive, XLT, crew cab, 3:55 gears, SRW
Tires/Wheels: 245/75R17
Speed: 60-65 mph
Error Test 1: 10 miles traveled, odometer read 9.8 miles traveled
Error Test 2: 10 miles traveled, odometer read 9.7 miles traveled
Error: 2-3%
Error’s Effect on Mileage: 16.9 mpg Vs. 17.3 mpg

 

Thanks for the info, but there is already a thread going on this one.

 

That's a win for us!!! The warrenty will last longer

 

Yep. And the other part of the win is if your odometer is reading low, your speedometer is reading high so you're going slower than it says and may save yourself a ticket

My odometer is off by 2% which I confirmed with GPS, not mile markers and it didn't matter by any measureable degree how fast I was going so I'm not getting that part of the story. I suppose it comes into play that the tires change shape slightly at different speeds but it's hard to imagine that it would be enough to measure. In any case, that would still apply if your odometer was bang on at some speed.

 

A'yup. My speedo reads about 2% high too. Pretty much the same as it's been on my last two Ford trucks. Even my Corvette is off by about the same.

Not enough to worry about IMO. Not like our '66 Ford P400 panel delivery truck. Speedo read about 10 MPH too low at indicated 55 MPH (from the factory) and that was more than enough for speeding tickets for some of us who drove it before we realized there was a problem.

Joe