Speedo off 5%

[gregdacat]

Well it has been two weeks now and the honeymoon is still not over with my 2002 Boxster. One thing I have noticed is that the speedometer registers about 5% faster than I am really going. So, 40 becomes 42, 70 becomes 74, ect. The wheels and rims appear to be original so I do not think that is the issue.

It is does not bother me much. I can stay out of trouble more easily if it reads high than if it reads low. Is this a big deal to fix. If it is I can live with it?

Greg (Newport KY)
2002 Triple Black - Das Schwarzer Panther

[Jeph]

That's partially normal. I find my speedometer indicating consistently that I am about 2 miles faster -regardless if I'm going 10 or 100.

The cars are set up like that on purpose. Not sure why, but there are other posts about it here.

Very common. You are not alone.

[Samson]

My '01 does the same thing. After getting passed by a few angry minivans, I grabbed a GPS to see what was going on. Mine reads about 5mph high at highway speeds, so 78 indicated is actually 73 or so.

[jmatta]

Mine is off a consistant 4 mph to the high side ('02 S). Rather it be high than low.

[pbanders]

This issue seems to vary from car to car. I used a GPS with my car (Tip w/the optional 18's) and I found the GPS readings were no more than 1 to 2 mph lower than indicated by the speedo over a range from 40 to 90 mph.

[Lil bastard]

Porsche calls it a 'safety margin' and it is not constant at all speeds it runs between 3-5 mph.

Those with MY <'00 can find true speed (in kph updated 1:sec.) through the diagnostic program in the climate control display - code 20c.

[edevlin]

It seems to vary with tires as well. With the PS2's, my spedo reads about 3 mph high, with the Nexen 3000's the spedo only reads about 1 mph high based on my GPS unit.

Ed

[rick3000]

Mine is high by exactly 3 mph according to my GPS, and two speed targets. So at 40mph I am really doing 37mph.
I don't mind and I don't think there is any way to fix this, but you might be able to get the speedo recalibrated.