Speedometer reads 2 mph too fast. Fixable?
 

I have used a portable gps in a number of cars which shows driving speed. Every car has matched the speed the gps shows except mine. The speedo is 2 mph over the actual speed. Can this be fixed?

are you running stock tires for your make/model/year?

if so, a +2 mph difference, dont know if Porsche would fix that to be honest

had a BMW 540 speedo that was off by 8 mph due to up sizing of rims.

Tire size may be the culprit.. if the height is lower it shows more MPH..

Mike

2 mph?

Is it enought to even worry about?

Mine does the same thing but I think it is more liek 3-4 mph for my car. I'm not that worried about that unless it was like 10 mph

Hmmm. I don't know. An $81,000 car. It'd be nice if it were accurate.

I am running stock turbo look 18" rims and spec tires.

+- 2mph i consider pretty accurate myself..

Absolutely right. It is pretty accurate.

:confused:

mines 4mph off...i can see it see it aeveryday because my escort 9500 shows the speed on it lol

last 2 p-cars i had were 3 mph over --

Get it recalibrated at an Indy shop if you want it 100% accurate.

I don't think there is a car in the world with a 100% accurate speedo.

I've got this problem too, my 2002 996tt's speedo is 3 mph too fast. It has stock wheels right now, but I'm going to put on the 1'' larger 997tt wheels soon and am waiting to see how the new wheels affect this (although I'm keeping ride height within 3/12 of an inch, so probably wont' affect).

If it was too slow, that'd be fine, but I'm annoyed its too fast because its putting 6% (at 50mph average) more miles on the car than I"m actually driving. It does seem like everyone who's noticed this problem is it being too fast, maybe Porsche is trying to make us think we are going faster than we are.

"Officer, my speedometer must be way off. It shows around 25 mph less than what you clocked me at - damn German electronics!"

Mine is 3mph off (high) as well.
It appears to be generalized to me.

Hahaha... both mine read 4 over and my Audi reads 2-3 over... it's a German thang....celebrate!!!!

Well looks like it is systemic, so that eases my nerves a little bit. Still, aren't you guys frustrated that an extra 3-8% of miles are being put on your car from this problem?

Perfectly normal. All car manufacturers calibrate their speedometers to read a few percent high. It is so you can't hold them liable for speeding. (I can't recall where I read that.)

In many countries the legislated error in speedometer readings is ultimately governed by the United Nations Economic Commission for Europe (UNECE) Regulation 39[4] which covers those aspects of vehicle type approval which relate to speedometers. The main purpose of the UNECE regulations is to facilitate trade in motor vehicles by agreeing uniform type approval standards rather than requiring a vehicle model to undergo different approval processes in each country in which it is to be sold.
European Union member states must also grant type approval to vehicles meeting similar EU standards. The ones covering speedometers [5] [6][7] are similar to the UNECE regulation in that they specify that:

• The indicated speed must never be less than the actual speed, i.e. it should not be possible to inadvertently speed because of an incorrect speedometer reading.

does that settle it for some of you guys ?

:cool:

It's probably for the best for me :p

I noticed several years ago that my speedo read 3 MPH faster than indicated by the local radar-activated "Your Speed is ___ " signs when I was driving around 30 MPH. I was concerned because I thought it meant that my speedo was reading 10% too high. What I learned was that the speedometer on 996s is calibrated to always 3 MPH high on purpose. So, even at 70 MPH, it only reads 3 MPH too fast, which is not a problem as long as you know that.

Where'd you learn that?

Mine is off by 3 at all speeds. I have notice that most people have reported in the past that theirs are off by 3. Given what has been said about calibration legislation I think that German electronics are very accurate... they are all about 3mph high on purpose.