Tire size with GPS

[bigdawg04]

I do not own a GPS but would like to set the tire size from a GPS so the ole speedo will be correct. I currently have 265/75/16 on my 2007 2500hd
Can anyone with a GPS let me no what the correct tire setting would be , Thanks

[jimmycurtisjr]

I have the same set up you do and set the tire size to 30.5 and came out dead on.

[rydnhi4x4]

I have 285/75/16 on mine, but I had to enter 265/75/16 to get my speedo right on using a GPS.

[bigdawg04]

Jimmy I take it you got your settings from a gps ? Anyone else ?

[cowdoc]

I have 265/75/16's as well. I use 244/75/16 and mine is dead on with my GPS.

[jimmycurtisjr]

Yes I used my GPS to get mine dialed in. From What I've heard it is the most accurate way.

[countrymac]

I have 285/75/16 on mine, but I had to enter 265/75/16 to get my speedo right on using a GPS.

When you had yours set at 285/75/16 was your speedometer slower then what your GPS stated or faster?

I used Diablo to change my tire size but it doesn't seem to have changed my speedometer at all which appears to be 2 mph slower then what the GPS states.

The truck came factory with 245/75/R16
Currently the truck has....... 285/75/R16 which is what is programmed using Diablo...

Any help is most appreciated.

[rydnhi4x4]

When I used the tuner to set the 285's it didn't change it all. I just kept playing with different sizes until I got the right size which was 265/75/R16.