This is common with German cars (speedo reading higher by about 5% than actual). IIRC it is because of an asymmetry in German law - they're penalized for underreporting the speed but not so much for overreporting it. So there is a bias to be sure not to underreport and thus speedos on average are set higher than actual.

My 997S seems to be right on to the extent that I can tell/check.

 

3-5 mph off depending on speed. Speedo showing i'm going faster.

 

The speed you see is not used in the odometer, the car usually knows exactly how fast it is going. On many cars you can see the actual value by hitting weird button combinations to get into a service mode in the bc, haven't found out how to do it on the 997 though.

 

1mph faster in my 997 than my Vbox

 

Also, I believe there is a hefty fine involved when the speedometer reports speed less than actual (either under German Law or an EEC rule).

 

My speedo in my 997 is about 3mph off... reading too high. Kinda annoys me. So when I think I'm going 40, I'm really only going 37.

My S4 has been spot on... I pass the same radar sign every morning on the way to work.

I wonder how far off it is at 70? I'm hoping still just 3mph.

Is there any fix for this, or just accept it? lol

 

All cars (ok maybe not ALL but most) at the upper end of the scale (150+) read incorrectly. That is why they always use GPS when doing recorded top speed runs.

 

Lol... is there a reason for this?! Did they spend all the money elsewhere?

 

A few years back, Car And Driver magazine tested a variety of vehicles for speedometer accuracy and the results were interesting. They didn't test a Porsche but the worst offender-- if I remember right-- was a BMW that read 7 mph optimistic at 60 MPH! IT read 60, but you were only going 53 mph. The most accurate vehicle-- a Chevy Silverado truck that was only 3 mph optimistic at 60.... Go figure. All vehicles read that they are going faster than they really are....

 

My 09 997S reads 2 mph high on an indicated 60 mph. I've tried a couple of GPS units and the results are the same. The car speedo is off by about 2%.

 

I find it impossible to believe they can't make an accurate speedo, and I find it very hard to believe they would make it inaccurate on purpose...

So what's the story?

Again, my S4 is dead on... so it's not a German thing, or at least not anymore.

 

Not 100% but I am guessing it has something to do with being analog and at higher speeds it just isnt capable of keeping up.

 

Mine reads off at a constant speed....but yes, the digital can't keep up when you're under hard acceleration. I've tested that!

 

OMG ! Speedometer error conspiracy has been uncovered, details at eleven. Great headline but hardly worth having the vapors over. If you're leasing a car and going so far over the mileage limit that it would cost you $ 1000's you need to quit leasing cars. As for the warranty, service your car by the book and most manufactures will over look the mileage within reason. However, I can sleep better knowing the conspiracy has been uncovered and that soon the government will hold Senate hearings to look into the matter instead of doing anything that would actually benefit the citizens of the USA.