Hey all thanks for reading!

I did a search and couldn't find anything recent on this subject but wondering if anyone had figured out a fix.

I had a 3 hour drive this weekend and decided to take the turbo... I was on the highway and was cruising along at my normal 80 in a 70 and looked at my GPS and it said 75. hmmm... so I went to a tie breaker and downloaded a digital speedo for my iPhone and sure enough...75.

I guess this does not bother me too much as it should keep me out of trouble although I'm kinda **** about my 996tt but after I was thinking, maybe the miles are off too...would be high! now that I will not tolerate as these cars are so valued off miles...

so I downloaded a miles app and decided that a mile was too short so did a 10 mile test. after the car read 10 miles, the GPS from I phone read 9.73. Not bad but off in my opinion.

I have stock tires sizes and stock rims.

Would my Porsche dealer be able to calibrate ? am i being stupid? not really sure if "this is normal" sits with me too well as again, these cars are valued off odometer reading first...

any thoughts?

thanks

 

I noticed this as well on my '03 996TT - speedometer. My external GPS would register @2-3mph lower than my speedometer showed. My other car = spot on.
I did not test my odometer.
I have stock wheel/tire sizes

 

HI,Someone posted way back when that there was a MPH recalibration for tire sizes in the control unit,I have larger diameter tires then stock.
So,I went to dealer and they hooked my car up,Its not the case on our 996 series...It is on the 997 series though..

 

I have read many posts on this and it's normal for the speedo to be off but not the milage. My Cayenne is spot on.