General rear gear question

[newguy]

I am still trying too narrow down my choices and bite the bullet... quick question:

If a car has already has gears in it, and the previous owner did not have a handheld tuner OR the speedometer recalibrated, does this mean the odometer is incorrect??

 

[BLWNMACH1]

Yes...

 

[newguy]

so if there are 3.73s in the car, the mileage will read higher than actual???

 

[Chief Gilly]

less

 

[newguy]

actually, i was talking to a guy that has his own used car store and repair shop... he stated only the speedo reads wrong (i know you can correct with tuner though; mine is sct)

says odometer will still be correct??! i kind of want to believe him(think could make sense), but not sure