Whats "speedo error"?

mikesride · mikesride's Garage

I see often folks talking about "speedo error" and claiming that your posted speed is probably 10Mph high. My last two speeding tickets (including todays

) would show that my speedo is 100% accurate at lest up to speeds of 110Mph. Does this mean my speedo has been re-calibrated by a PO? Or does this speedo error start factoring in somewhere after 110?

Rick V · 08-06-2012, 04:15 PM

mikesride · mikesride's Garage

^^^^I thought I got ride of that pic!^^^^ Thats one of the funniest ever!

Rick V · 08-06-2012, 04:24 PM

Well you knew it was going to happen and my wife even commented "Someone was going to have to do it" She wasn't even surprised when she saw it was me.

herr_oberst · 08-06-2012, 04:30 PM

Banana-hammock notwithstanding, in my 911, when compared to my GPS, there is a non-linear inconsistency. It's not even close below, say, 60, but around 80 it starts to become more accurate.
From what I've read, Porsche speedometers are all over the map, accurate-wise.

id10t · 08-06-2012, 04:30 PM

I'd check with a GPS on a long straight road

gprsh924 · 08-06-2012, 04:36 PM

My 530i is reads 4-5mph high compared to my gps around 80mph. (ie: GPS is reading 80mph, speedo reads about 84-85mph)

Outback Porsche · 08-06-2012, 05:06 PM

hehe, reading my mind Rick. I was just looking for a similar pic to post

red-beard · red-beard's Garage

There are several issues. Some is wheel/tire improper size. Some is instrumentation error and some is simple calibration of the guage.

On my old BMW X5, if I read the ODB-II directly, it perfectly matched the GPS reading. But the dash guage read high.

Grady Clay · 08-06-2012, 07:49 PM

LET ME TELL YOU A STORY

Many years ago, I had a Rennenhaus customer (a practicing attorney) who had us build him a ‘special’ speedometer.
When the 911 was going 80 mph, the speedometer indicated 50 mph.
He took his 911 to two speedometer shops and got documentation as to the ‘inaccuracy’ of his speedometer.
I think he presented this in court and had speeding tickets dismissed.

Over the years, many others (including some Judges) used this speedometer.

Best,
Grady

Bill Douglas · 08-06-2012, 08:59 PM

I've got a story for you too. I know I've told it before but us old gits always tell the same story over and over again...

In New Zealand we are a kilometers country and the speedo in the 911 is in miles and hour. A GF borrowed it and came back saying there is something really weird about the speedo. I was driving around at 100 but seemed to be flying past everyone else.

flatbutt · 08-07-2012, 08:04 AM

My R1100S has an optimistic speedo. It's about 8% high throughout the range. 100 indicated would be about 92 actual.