Speedometer Error

[Flavor 987S]

I trust my Garmin GPS's (I have 2) as being accurate. The Boxster (2006) shows me going 2 MPH faster than actual and the 1997 993 Turbo is dead-on. Funny how Porsche got it right +14 years ago!

This is all very common, BTW.

[DFW02S]

My speedo consistently shows 4mph faster than my GPS and pacing another car and matching speedos.

For Porsche, that little error in the 3 to 4% range saves them on warranty repairs, the miles go on just a wee bit faster.

I bet their accounting group knows exactly how much they save through this method.
Of course, it could be just tire variance, right?

[Highlow]

My car shows consistently 3mph over actual(radar) speed. This is for anything over 10 mph, I've never tried less.

[Flavor 987S]

Originally Posted by DFW02S

For Porsche, that little error in the 3 to 4% range saves them on warranty repairs, the miles go on just a wee bit faster.

I bet their accounting group knows exactly how much they save through this method.
Of course, it could be just tire variance, right?

Myth. Urban ledgend. The mileage on your DME is very accurate. And this is used for warranty claims. You should request a DME scan the next time your at the dealership or from someone who can read it.

[urban_legend]

Porsche speedometer an easy 5% fast. Audi dead nuts on.
Audi wins...oh wait... Audi check engine light flashing again ;(