Thanks for the replys guys. I was going the opposite way for some reason. I thought that my speedo was reading higher than than I was really going. So you are saying when you put bigger tires on you are putting less miles on the speedo than what you are actually going?

Sorry for the ignorance....

 

Because my gps states I am going 65 with the new tires, speedometer states I am going 69. So I am putting more miles on my truck than what I am really doing.

Do you think that my speedometer has been change? I am the second owner so maybe the speedometer has been mess with from stock (although i don't think so because it didn't have a leveling kit so I don't think that larger tires have been tossed under it ).

 

That is correct.

 

Ok gonna try to make this make sense. It does in my head but not sure if imma get it out right here.
U guys talk about getting a programmer instead of recalibrating your speedo. Does the programmer fix your speedo or are u just using the programmer as you MPH checker?
Also if the programmer doesnt fix your speedo than the whole time u are are running bigger tires without having the speedo recalibrated u are putting less miles on the ODO than what u are really driving right?
As an example (not exact figure) say i go on a trip and my odo says it took me 300 miles to get there depending on the tire size i would have actually drove say 340 miles.

 

On top of the programmer actually giving you a little boost in HP, there are parameters in the unit that will actually allow you to change the outside diameter of the tire so your speedo/odometer will be correct.

 

Than shouldn't my speedo speed read less than my gps speed not more?

Thanks

 

No, the programmer does recalibrate the speedometer and odemeter. It's just done with a program in the trucks computer as opposed to the old method of having a gear in the transmission. The computer program is told what size the tires are now and it recalibrates the speedometer.