OEM Tire Circumference Values

[Ducati1098]

hmmm....that is the correct mm for that size tire. not sure then

The calculations won’t match. Nitto says my 37’s inflated Diameter is 36.85”
Which would be 2940.5mm in circumference.
Yet only 2800mm in forscan matches every GPS perfectly.
The only way to get an accurate speedometer is trial and error using a GPS.

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[BasedBronco]

Hm, I'll add an asterisk to the original post. Sorry for posting then going MIA. We had a death in the family so my Bronco hasn't been a huge priority.

I'll try to go back and confirm the numbers. Anything I put in the table was from a dealership-provided VIN with OEM tire specs shown on the listing, but I suppose there could always be mismatches or changes after delivery.

 

[OscarHTX]

Putting some Wildtrak take offs on my BD, so I change to 2653 in Forscan?

 

[Algro]

Putting some Wildtrak take offs on my BD, so I change to 2653 in Forscan?

I did the same as you, 4 door BD with Wildtrak take offs and tried 2741 mm and I was 3 mph slower than the speedometer. I saw someone had used 2501 mm for a Wildtrak wheels. So I just changed my setting to 2501 mm yesterday and now my mph matches my gps sensor.

 

[OscarHTX]

I did the same as you, 4 door BD with Wildtrak take offs and tried 2741 mm and I was 3 mph slower than the speedometer. I saw someone had used 2501 mm for a Wildtrak wheels. So I just changed my setting to 2501 mm yesterday and now my mph matches my gps sensor.

Mine showed 1 mph slower than gps. Not sure how accurate gps was. But I think as tires wear down itll even out some. Im good where I'm at.

 

[objctvsm]

Went to the Bronco Barn in Las Vegas today to get speedo calibrated. Awesome professional place, by the way. They told me that you only get error / code messages (4x4 / AWD) after changing the MM in Forescan IF you enter a non-factory supplied number, such as a number you obtained by measuring it yourself or using tiresize website. I took the information in this thread with me for the OEM BdyCM Circumference and they used that number, 2475. It took them seconds to change it and we confirmed the accurancy with GPS. It is dead on balls accurate now. So, do not follow the advice most of the Internet gives about measuring yourself, unless you want error messages that you'll need to clear. Thanks Bronco6G for the assist! OH, they also said if no calibration was done it would have zero impact on anything like shifting and transmission for all of you worriers like myself. I only went from the base 30s to 32s so maybe if it was 30s to 35s/37s that might not be case. The guy actually said 2-3 MPG off is within normal acceptable limits for speedometers. He was almost talking me out of it but I wanted it perfect. It cost me and hour of labor but it was well worth it.

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