# Annoying Speedo error 540i-6spd



## glankford (Mar 23, 2004)

I have an annoying problem with my speedo on my 99 540i. The needle always reads faster than the trip computer. The computer reads an accurate speed, but the needle is off. I don't know if it is always off the same amount or if it is proportional to speed. 

I thought about popping the needle off and repositioning it, but that seems kind of a hokey fix.

I do need to take my dash apart due to a few lines of missing pixels, so if I can fix the speedo problem while I am in there, great!

Any IDEAS?

Thanks,
Garrick


----------



## Sands (Apr 7, 2004)

German TUV law requires that the speedo never reads slower then actual, regardless of the tire size on the car. It is typically about 4-5% too fast. The computer is correct ( or as close as can be expected, given tire diameter variation.)

No dice on fixing it. It's in the software - at least I haven't found a fix for this yet. though I haven't asked the dealer if they can re-calibrate it.


----------



## 545iSMG (Feb 25, 2004)

This margin of error is by design across the BMW line. I always thought it was something they did to cover their A's from lawsuits, etc.

Unfortunately, since it's off by a percentage and not a fixed amount, it's impossible to simply pop the needle off and re-position it (that technique probably wouldn't work even if it was off by a fixed amount).


----------



## PropellerHead (Jan 3, 2002)

545iSMG said:


> Unfortunately, since it's off by a percentage and not a fixed amount, it's impossible to simply pop the needle off and re-position it (that technique probably wouldn't work even if it was off by a fixed amount).


Actually, someone did something like this sucessfully about two or three years ago and even wrote a how to. It involves removing the cluster and playing with a spring behind the needle. It stopped being a possiobility for me when the guy said he had to rewind the spring after one mistake. I have no idea how to do that. Anyway, the way he did it was to make an adjustment, installl the cluster, go for a drive and reset the AVG speed function in the OBC to compare his real (digital and accurate) speed with what read out on his speedo. He would then return home and do it all again. Took him 3 or 4 tries if I remember correctly.

You cannot totally eliminate the error, but you can come awful dang close.


----------



## 545iSMG (Feb 25, 2004)

Okay...I guess I meant "NEXT TO impossible" instead of just "impossible!"


----------



## Greco (Feb 16, 2003)

Actually in your owners manual speedo allows for 10% error in indicated speed. More than 10% you should get it readjusted by the dealer.


----------



## glankford (Mar 23, 2004)

That sounds ambitious. Couldn't you just put the rear tires up in the air using jackstands, and set the cruise control? Once your speed is constant, dialing it in would be easier (and safer) than going for a drive. You could have it apart and adjust it in real-time.

I like that idea though. I may do that one of these days I get bored and run out of other projects. I still need to look @ my auto dimming (or lack thereof) mirror.

10% off?! WTF? These machines are SO stinking precise on everything else. I have never owned or driven a more exact machine. It seems that they could do better than 10%.

He probably had to rewind the spring after taking it apart the wrong way (or taking too much apart) and the spring popped out. You have to put it back the way it was, kind of like winding a clock spring.

Thanks,
Garrick


----------



## johnf (Sep 16, 2003)

Sands said:


> German TUV law requires that the speedo never reads slower then actual, regardless of the tire size on the car. It is typically about 4-5% too fast. The computer is correct ( or as close as can be expected, given tire diameter variation.)


Actually, it is an European-wide regulation that the speedometer may not underread, and may overread by up to 10% + 4 km/h. European speedometers typically overread by a few km/h at 160 km/h (100 mph) which is not so much as to be annoying. I don't know why some U.S. speedometers are considerably worse. Perhaps, BMW NA adds extra margin because they have much less control over the tires their customers put on their cars? In Germany, the automakers can depend on the TÜV. They decide what sizes you may use and will declare your car unroadworthy if the tires would make the speedometer underread.


----------



## glankford (Mar 23, 2004)

The tire size is a good point. One of the reasons I would like to fix it is because I don't want to get used to speeding extra because my speedo is off, and then get in another car and get a ticket. I like to drive just slow enough to not get caught, so the speedo error is another thing I need to think about and compensate for now.

Thanks for all the help!

-Garrick


----------



## Sands (Apr 7, 2004)

If you know how much faster your speedo is, you can use a tire size calculator to adjust the sidewall ratio up a few. probably the only practical way to do this.


----------

