Tire size does make a difference ?

[MikeHardison]

One advantage of getting hooked up with Forscan is that I found out the tire size in the BCM module was incorrect for my tire sizes.. I bought the 21 Ranger XLT last year and noticed that the gas mileage wasn't up to spec and routine trips that I make had slightly shorter distances than my other vehicles. I just put in the new values and we'll see on tomorrow's drive to NC.

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[rydfree]

One advantage of getting hooked up with Forscan is that I found out the tire size in the BCM module was incorrect for my tire sizes.. I bought the 21 Ranger XLT last year and noticed that the gas mileage wasn't up to spec and routine trips that I make had slightly shorter distances than my other vehicles. I just put in the new values and we'll see on tomorrow's drive to NC.

Always check to verify accuracy with a GPS app . I had to tweak my values a couple times to get it spot on .

 

[Joeiconic]

Change tire size for Speedo accuracy, but measure mpg’s at the pump.

 

[Dgc333]

Change tire size for Speedo accuracy, but measure mpg’s at the pump.

Still need the speedo to be accurate to get accurate mpg numbers regardless of whether you calculate by hand your mpg or use the trip computer. A discrepancy between the actual overall tire diameter on the truck and the calibration factor in the as-built data will impact how many miles the odometer records in comparison to how many miles you have actually have driven. If the as-built calibration factor is for a smaller tire than what is actually on the truck the odometer is going to record less miles driven than you actually have gone. This will result in artificially lower gas mileage when you calculate mpg.

Also, the trip computer has a calibration factor that can be adjusted to make it accurate. I adjusted mine after about a 2000 miles of recording both the trip computer and hand calculating. I my trip computer is within +/- .2 mpg of hand calculating. That +/- .2 is more than likely not filling the tank to exactly the same place each time.

 

[DukeCanBuildit]

Still need the speedo to be accurate to get accurate mpg numbers regardless of whether you calculate by hand your mpg or use the trip computer. A discrepancy between the actual overall tire diameter on the truck and the calibration factor in the as-built data will impact how many miles the odometer records in comparison to how many miles you have actually have driven. If the as-built calibration factor is for a smaller tire than what is actually on the truck the odometer is going to record less miles driven than you actually have gone. This will result in artificially lower gas mileage when you calculate mpg.

Yes, with bigger tires, the odometer will register lower miles than are actually driven. That might not be a bad thing if a warranty claim is involved when your odometer reads very close to the mileage limit but it’s actually off by 5% or more in your favour because of those bigger tires.

Now, can anyone think of other things that would be impacted by the odometer reading?

 

[MikeHardison]

Still need the speedo to be accurate to get accurate mpg numbers regardless of whether you calculate by hand your mpg or use the trip computer. A discrepancy between the actual overall tire diameter on the truck and the calibration factor in the as-built data will impact how many miles the odometer records in comparison to how many miles you have actually have driven. If the as-built calibration factor is for a smaller tire than what is actually on the truck the odometer is going to record less miles driven than you actually have gone. This will result in artificially lower gas mileage when you calculate mpg.

Also, the trip computer has a calibration factor that can be adjusted to make it accurate. I adjusted mine after about a 2000 miles of recording both the trip computer and hand calculating. I my trip computer is within +/- .2 mpg of hand calculating. That +/- .2 is more than likely not filling the tank to exactly the same place each time.

Today I drove my normal route to NC. After inputting the correct tire circumference, my mpg (highway) was 27.4 vs 24 on the incorrect tire size. Also the trip odometer was what I expected, similar to my gps app and Google maps. And you're correct, a smaller tire value gives less miles on the odometer.

 

[Msfitoy]

One advantage of getting hooked up with Forscan is that I found out the tire size in the BCM module was incorrect for my tire sizes.. I bought the 21 Ranger XLT last year and noticed that the gas mileage wasn't up to spec and routine trips that I make had slightly shorter distances than my other vehicles. I just put in the new values and we'll see on tomorrow's drive to NC.

I had programmed forscan to adjust for my 285s but only got within one MPH above actual GPS speed...my dash shows 17-18 average around town...my OBD shows 21 MPG...I'm going with 21...

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