JStuart

I noticed as I drove by (and slowed down) one of those neighborhood radar displays that my speedo indicated 39-40...the radar display showed 35? Could low profile tires make that much difference?

Jay

GabiOsz

Mine seems to be around 7% out acording to my sat nav; stock wheels. My old Merc was the same, it's quite normal in most cars.

1998C2S

Mine is unbelievably accurate, according to GPS. I was amazed to see it within 1 mph at the 80 mark. My Audi is bang-on as well - Now the Ducati is another story - I think the bike manufacturers try to fool you into going slower than you could/would if you knew your real speed of travel.

jimbo3

There was a thread on this awhile back and, IIRC, most fell within a couple of percentage points. My digital read-out is spot on, while the analog reads within 3%.

If you changed the circumference of the tire from stock, the accuracy of the speedo will be off proportionately. What are your tire sizes?

-Jim

pcar964

Mine is also very accurate, at least according to the police-state speed signs. Never more than 1 mph off. Of course, that's at normal (sub-80) speeds. I'll need to go faster to get a more accurate comparison

The Antenna Man

I guess every car is different

GabiOsz

at 100mph on my satnav my digital speedo reads 107mph, of course my satnav could be wrong.

SJB993

Mine is about 10% fast compared with my satnav. My other two cars are more or less spot on.

I don't understand why an electronic system can be so far out. Maybe electronics ain't Porsche's thing?