Speedometer Error
 

I recently put new tires on my 2001. I used the exact same size as the originals.
On a recent road trip with a friend I seemed to always have to go faster than he was to keep up. This lead to a speedometer check on a true measured mile several times, plus a GPS reading. Each showed a speedo reading of 80 mph to be a true speed of 77 mph. That'll rack up some odometer miles huh? I have never tested the speedo previously. So, not certain if this SOP for the Boxster or the result of new tires. The only thing different on the new tires is going from a summer tires to an all weather tires. Tire Rack says that shouldn't make that much difference.

Grasping at straws, could I be so lucky as to discover a black box adjustment for correction?

Dusty

For some strange reason, all Boxsters are about 4 mph off on the speedo. I tend to like it because if the speedo shows I'm driving at 60 mph, it really is around 56 mph.

Others will comment, but for some reason the factory calibrated it this way.

This is normal.
It doesn't affect the odometer.
You can't adjust it.

+1

Found this out while running rallies.

Speedo Error Thanks
 

Thanks Guys. I guess I never knew that Porsche calibrated the speedo that way. I am a retired GMer and run will a couple of GMers in 'Vets and catch all kind of flack for driving a wimpy German and dare not tell them the speedo is off. They are quick to tell me I just can't keep up, Haha. I have to remind them I have 2 less cyl. and they haven't left me in the dust yet.

Thanks againg....Dusty