Speedometer difference

[Maverick997]

Just noticed that my speedometer is 4mph faster than any of my gps devices.....anyone else noticed this? I have 20" wheels from the factory but assume they would calibrate for them.

[GarbageMan]

It will be more of a variance at high speeds. BMW will hand you some sheet of paper if you go ask them about it (their disclaimer). I have no idea why they feel the need to have the speedos off so far. I'm forever calculating in my head about how fast I'm going as I look at the speed in the heads up. This and the "no manual dipstick" thing are my two biggest peeves. The fact that owners don't bring torches and pitchforks to the dealership about the latter issue tells me that most BMW owners know little about mechanical maintenance, and it also says that I'm a redneck...

[jayhawk785]

mine is 3 mph slower than my gps device...

[RPiM5]

3-4mph is the standard. I'm running snow tires on my stock 20" 343M's and the speedo difference is 6-7mph off. Very annoying. I'm constantly looking at my GPS speed on Waze to see my actual speed.

[13M5F10]

Same issue here ... 3 MPH over

[Ex_Stig]

Margin of error.

[Blackraven]

This is an interesting topic.........especially when contesting between what is displayed in the car speedometer versus the speed reading detected by police and traffic enforcers with speed guns.

[johntomferg]

Good article:
http://www.caranddriver.com/features...ometer-scandal

This has been a sore spot for me in my BMW experience with the M5.

I get that any manufacturer may want to have a policy that says their speedometers will be intentionally optimistic as set from the factory. What I don't get is the need for the document posted above [I also received this very early on in ownership], and the desire to prevent the end user of the product from adjusting it to meet their specific desires.

I'm not talking about the lack of adjustment being in the menus, hidden or otherwise, though it would be awesome if it was... NO, I have found 0 dealers that will change it at request and zero Indy's, and I have heard of zero persons that ave achieved correcting it via 'coding'.

Poor decisions BMW...very poor.

Preemptive response to inevitable post about German speedometer laws: I love hearing about German law requirements when I don't live or am not in Germany probably just about as much as Germans love being dictated "realities" of US law when they are not in the US. :-)

[AP]

I thought by law speedometers had to read slightly over. If they were the other way then you could end up unintentionally breaking the speed limit and ending up in trouble, even if it is only a few miles an hour.

[Maverick997]

Thanks for the confirmation guys......probably saved me a couple of close calls on being over the 9mph limit��

[Scott@Radar-Mirror.com]

Every BMW speedo is at least 5% over your actual speed. As I recall AMG's I've owned were a lot more accurate.

[Lawaia]

63 on the speedo will read 60 on gps.

BTW, does this also affect the accuracy of the odometer?

[johntomferg]

Originally Posted by Lawaia

63 on the speedo will read 60 on gps.

BTW, does this also affect the accuracy of the odometer?

No (assuming stock tire sizes). The reason is that the car is programmed to capture the accurate/correct speed. The display is then programmed to give you an inaccurate result via (in-)correction factor.

Think about that for a minute... curious to know if it ticks you off as much as it has me over the years.

I just drive 'faster' to compensate which means I probably speed more (not more often but in greater incriments) now than I would if the speed info presented to me was accurate.

[MichaelJohn]

I have a Honda motorcycle and the speedometer is dead nuts on with my GPS. If Honda can do that on a motorcycle that is 1/10 the price of my M5 why can't the great German engineers get it right? I find it really annoying.

[Rearview]

Originally Posted by Maverick997

Just noticed that my speedometer is 4mph faster than any of my gps devices.....anyone else noticed this? I have 20" wheels from the factory but assume they would calibrate for them.

Guess that means a better 0-60 time!

[Lerxst M4]

My E90 M3 was also 3 mph over (same as my M5). I thought I had read that it was intentional by BMW.

It doesn't bother me even though I am always 'doing the math' when I drive. lol

[E90Fleet]

As your tread wears down your speedo speed in relation to your GPS speed will change.

Also remember the car has to be setup by BMW to be within limits for all allowed OEM wheel sizes.

The rolling diameter for a well worn 18" tire can be quite different to that of a brand new 20" one. So its impossible to have it perfectly accurate for all possible combinations of tire sizes and tread depth.

[johntomferg]

Originally Posted by E90Fleet

As your tread wears down your speedo speed in relation to your GPS speed will change.

Also remember the car has to be setup by BMW to be within limits for all allowed OEM wheel sizes.

The rolling diameter for a well worn 18" tire can be quite different to that of a brand new 20" one. So its impossible to have it perfectly accurate for all possible combinations of tire sizes and tread depth.

If you are making the point that the speedometer cannot be perfectly accurate all of the time then that is a given... but we are expecting it to be much more accurate than it is and BMW's accuracy is unacceptable regardless of tire wear.

To this case and point, tires don't increase in size as they wear.
If today, I put a new tire on my car its diameter is as large or as tall as it will ever be. Today it reads 74 mph indicated when driving 70 due to the un-correction that BMW applies.

A year from now when the tire is worn and the diameter is reduced due to is maximum wear of 7/32 thread use.... what does it read then? When I am doing 74 indicated - am I doing more or less than 70 actual? A smaller diameter on the tire will mean that the distance covered is even less per each rotation. So that means it will be even more off and the actual speed of the vehicle will be less than 70. So inaccuracy increases in this scenario over time.

If the scenario (which does not exist today) is that the un-correction factor resulted in the display being slightly less than actual speed when the tires are new, then that improvement and justification of tire wear would be perhaps more believable.

In the case of the M5, which *is* the car we all bought, you have 19 inch and 20 inch wheel/tire combinations available. In all cases near stock sizes the displayed data to the driver is inaccurate... new tires/old tires. At what point does it become accurate to promote the "awesome" engineering and "precision" of BMW?

/Rant off

[GarbageMan]

Originally Posted by johntomferg

If you are making the point that the speedometer cannot be perfectly accurate all of the time then that is a given... but we are expecting it to be much more accurate than it is and BMW's accuracy is unacceptable regardless of tire wear.

To this case and point, tires don't increase in size as they wear.
If today, I put a new tire on my car its diameter is as large or as tall as it will ever be. Today it reads 74 mph indicated when driving 70 due to the un-correction that BMW applies.

A year from now when the tire is worn and the diameter is reduced due to is maximum wear of 7/32 thread use.... what does it read then? When I am doing 74 indicated - am I doing more or less than 70 actual? A smaller diameter on the tire will mean that the distance covered is even less per each rotation. So that means it will be even more off and the actual speed of the vehicle will be less than 70. So inaccuracy increases in this scenario over time.

If the scenario (which does not exist today) is that the un-correction factor resulted in the display being slightly less than actual speed when the tires are new, then that improvement and justification of tire wear would be perhaps more believable.

In the case of the M5, which *is* the car we all bought, you have 19 inch and 20 inch wheel/tire combinations available. In all cases near stock sizes the displayed data to the driver is inaccurate... new tires/old tires. At what point does it become accurate to promote the "awesome" engineering and "precision" of BMW?

/Rant off

Amen. As much as I love the car... This is silly...

[boots]

Originally Posted by Rearview

Guess that means a better 0-60 time!

Lol. I'm with cha

[apexlocator]

I thought it was just me....the m5 shows about 4-5mph faster than speedo signs that measure your speed as you drive by.

[Boss330]

Originally Posted by AP

I thought by law speedometers had to read slightly over. If they were the other way then you could end up unintentionally breaking the speed limit and ending up in trouble, even if it is only a few miles an hour.

By EU law, speedometers have to show close to real speed, but never less than actual speed.

In the US, it is a +/- 5mph limit. Your speedo can, legally, show as much as 5mph less than actual speed...

https://www.law.cornell.edu/cfr/text/49/393.82