I just had a lift put on my 2012 JKUR. I went crom 32x10/17 to 35 12.50/17. I have not put the programmer on it yet. I thought I would see how bad the speedo is off. I thought I would be able to use my navi speedo until I put the programmer on . It appears that the navi speedo is synced with the regular speedo and does not use a satellite like I had assumed. Does anyone know anything about this?

 

Chrysler had this done for a reason. If the vehicle was stock and the nav and the dash didnt agree, think of the number of service visits to fix a problem they have no way of fixing.

By syncing them, they will always match and therefore no service visits which cut down costs.

People that mod their vehicle or change tire sizes are no longer in spec and therefore are not a concern of the dealership anymore.

 

The simple answer is that the radio does not use GPS to calculate the speed. Instead it uses the speed given to it over the CAN bus, which is sent from the ECM, which does this speed calculation by the drive shaft rotation. This is also the same way the speedo gets its speed information. So they're always the same, because they both get the info from the same source.

 

Throw a standalone gps in there till ya reprogram.... if ya happen to have one.