Speedometer calabration question?

[roadrunnertex]

I have a new speedometer kit for my coach it's calibrated for 11R-22.5 tire size which is 490 revolutions per mile.
On my coach I have 12R22.5 tires and they are 480 revolutions per mile.
Will the speedometer read high or low?
I can have the speedometer recalibrate to read 480 revolutions but was just wondering what the difference would be.
jlv

[Chopper Scott]

It will show that you are going 48 mph when you will actually  be going 49.

[Dreamscape]

Hey John,

What model did you get?

I have to set mine up and if it's a Dixson, maybe you can get me your dip switch settings....................Please. I have 10 dip switches. I have the same front tire size as you do. I just haven't had time to set them and then check it.



Paul

[gus]

Just borrow someone's GPS and check it out, they are very accurate. I use mine more than I do the speedometer which is not easy to read.