Incorrect speedo?

[onceover]

I was driving on a highway a while ago and played with my average speed counter in the DIS.

whenever i reset the average speed, it would jump up to my current speed, but the value on the DIS read about 10km/h less than what the actual speedometer read.

Shouldnt they be running off the same system? what could cause this

[Torqie]

I was driving on a highway a while ago and played with my average speed counter in the DIS.

whenever i reset the average speed, it would jump up to my current speed, but the value on the DIS read about 10km/h less than what the actual speedometer read.

Shouldnt they be running off the same system? what could cause this

Ive noticed that too, but also when I go by those signs that tell you how fast you are going my speedo reads about 5mph faster then what the sign says I am going. I am on stock wheels with 235/45(i think)/17. Going to get winter tires on tuesday though.

[yellorado]

i dont know if it means anything but ive noticed the same thing, but my speedo is about 10% fast also, so the average speed seems somewhat correct but the speedo isn't (on the cruise running 120kph, gps show 110kph actual speed)
ps: tires are the correct size...

is there something that can be adjusted through vag?

[texasboy21]

^^^me too about 5mph. thats weird

barrett

[yung turbo]

it might be because of your rims if you have any?

[onceover]

nope, stock rims, stock size.

wouldnt both things get the reading from the same unit? i dont see why not

[JoshDub]

maybe its just me. but i have never seen those speedo things on the side of the road say the same speed as the cars speedo.

[member]

mine speedo was off but i had 19's from stock 17's

[Torqie]

maybe its just me. but i have never seen those speedo things on the side of the road say the same speed as the cars speedo.

with my 97 integra it was right on with those... but maybe it was my teggy was off on the speedo.... who knows.

[diagnosticator]

I was driving on a highway a while ago and played with my average speed counter in the DIS.

whenever i reset the average speed, it would jump up to my current speed, but the value on the DIS read about 10km/h less than what the actual speedometer read.

Shouldnt they be running off the same system? what could cause this

Both displays use the same speed reference, but there is no reason the calibration must be the same. The digital display is more accurate than the analog speedometer. The speedometer calibration is intentionally (required by law,) set with a speed error so that the indicated speed is faster than the true road speed that the car is actually traveling at. I set my cruise control set speed, using the digitial DIS displayed value, not the analog speedometer indicated value.

[onceover]

really? whats the reasoning behind this?

[AudiA4Turbo22]

^^all audi's are the same they always show a 5MPH difference, but that works to our advantage.

[VAG_4ever]

very true. vw's are like that too.. if the speedo says you are doing 70 its more like 65ish.

safety issue.

[diagnosticator]

Supposedly, to avoid the problems that would result if the indicated speed is slower than the true road speed.

[Agro]

I had this issue on my Yamaha R1 motorcycle. I bought this little box called a "speedohealer" It let you dial in the adjustment in percentages. It simply was put in line with the speed signal wire coming from the tranny. I wonder if this is applicable on our car? That is if it is electronic speed wire not mechanical.

[Sammy7]

I've noticed that my speedo understates my speed by abour 5 mph. When I'm not in a big hurry and just driving the speed limit on the highway, I have to remind myself that I'm the idiot going lower than the speed limit and I need to speed up.

What's the correlation between the speedo and the odometer? Say if the speedo's recalibrated to show the true speed, would it throw off the odometer?

[Agro]

I've noticed that my speedo understates my speed by abour 5 mph. When I'm not in a big hurry and just driving the speed limit on the highway, I have to remind myself that I'm the idiot going lower than the speed limit and I need to speed up.

What's the correlation between the speedo and the odometer? Say if the speedo's recalibrated to show the true speed, would it throw off the odometer?

The speedometer directly coorellates with the odometer. If you are showing more MPH than you are really going then you are tacking on more miles, same goes for less MPH. This is why when people used to disconnect the speed wire, they would not put any miles on the odometer but they wouldnt be able to tell their speed.

[NorcalPB]

The speedometer directly coorellates with the odometer. If you are showing more MPH than you are really going then you are tacking on more miles, same goes for less MPH. This is why when people used to disconnect the speed wire, they would not put any miles on the odometer but they wouldnt be able to tell their speed.

Wrong. The car knows how many miles you're actually traveling even though the speed is off. On my b7 the millage pairs up exactly with my garmin unit and the garmin shows it to be 3-4 mph fast. When I take the car to 130 mph limiter it says 133-134. It knows how fast it's really going and therefor calculates accordingly. I have compared to mileage to friends cars when going to the same destination and it is the same.

A speed error is not required by law. Why doesn't Mercedes have to follow this law? Why does the b8 have no speed error? It's juts something thats meant to work to the driver's advantage so they won't find themselves traveling too fast.

[diagnosticator]

Wrong. The car knows how many miles you're actually traveling even though the speed is off. On my b7 the millage pairs up exactly with my garmin unit and the garmin shows it to be 3-4 mph fast. When I take the car to 130 mph limiter it says 133-134. It knows how fast it's really going and therefor calculates accordingly. I have compared to mileage to friends cars when going to the same destination and it is the same.

A speed error is not required by law. Why doesn't Mercedes have to follow this law? Why does the b8 have no speed error? It's juts something thats meant to work to the driver's advantage so they won't find themselves traveling too fast.

Maybe "Required by law" is not the correct term for this. However, there are government rules and policies stipulating that in order that speed indicated errors don't cause actual speed to be higher than the indicated speed, a built in error (or offset,) is specified in the calibration settings.
The indicated speed error offset, does not necessarily effect any other aspect, like the odometer.

[dirtybrd]

Most car speedos read fast.