yep you are correct this is a common bit on the e46 and i think all bmws

 

Nothing to be concerned about...completely normal.

Whether gov't conspriacy or the size of your wheels, there's a speed sensor that, from what I know, assumes a specific size of tire...so changes in that will affect accuracy (correct me if I'm wrong, folks). If you get a gps fix on long straight away, trust the gps. I know mine is off like 50' (don't know if THAT is normal), but on a long run, think gps is better.

I just saw the inside of the front wheel bearing, don't know if it's there on every bearing...probably...a flat ring of magnets...behind a plastic 'washer'...anyway, it sends pulses to the sensor behind, so speed is calculated based on the speed of that thing spinning and it assumes a diameter of tire to give you speed.

But, I've heard that every speedo is off to the low side anyway...to fool us into thinking we're going faster than we really are. Larger wheel/tires might correct that so you're accurate, but then you'd also be slower...so you got to chose!

Doug

 

Hey Doug. Long time no hear. The sensor at the wheel is an ABS sensor. In fact, they are at all 4 wheels. The vehicle speed is picked up at the vehicle speed sensor at the transmission. Chas

 

So that's what they were!

You know, Chas, when I said someone could correct me, I really didn't mean that! LOL

But, I guess the principal would be the same...around a fixed moving object, so when tires are larger, you'd have greater accuracy but slower speed...per the discussion recently on tire size/rotating/unsprung weight and where the weight is on the wheel.

Someone can correct me again if needed!

Doug

 

But, I've heard that every speedo is off to the low side anyway...

You are correct, sir, especially in Euro cars (American iron is usually spot-on, and have been for decades. Go figure). Besides, I think I'd trust $15,000,000,000 worth of government GPS satellite technology over a <$100-wholesale-to-manufacturer speedometer assembly... :woot:

 

For some reason this is somewhat a common issue with most German auto makers. Most of the time the speedometer reads too high a speed.

As I recall, my E46 reads about 3-4 MPH too fast?

You should also check to see if your odometer is reading correctly, using both the GPS and highway mile markers.

My wife had a 2003 VW Beetle and the speedometer would read about 5-6 MPH to high at highway speeds, however, the odometer was dead on. As I recall, VW claimed that if the speedometer was within 10% then that was considered normal.

My GMC Yukon is dead on for both speed and odometer as compared to my GPS.

I would believe a GPS long before I would believe a German speedometer!

 

My bmw is right on with my gps. I've had 2 ford escapes for company vehicles and they have both read 3-4 mph high at highway speeds. I thought american manu's did this intentionally as a form of speed control. The same with sportbikes, they always read high to make the driver think he's moving faster than he actually is.

 

No need for correction Doug. You are spot on. :clap: Chas

 

what he says is true, but with bmws it should also be noted that even with stock wheels etc the bmws still read above actual speed. its just built in to the car

 

Yes, tire sizes make a difference. Tread wear make a difference too, cause a new snow tire will have a larger circumference than a bald summer tire.

use this to check differences between tire sizes on a basic level:

http://www.miata.net/garage/tirecalc.html

I upgraded my tires and used BMW specified sizes (244/40/17 to 255/35/18) and knew that my new tires would leave my spedo 1.3% slow, so when the spedo said 60mph I was actually going 60.8 :read:

Weather BMW builds in a margin, I dont know. GPS can be pretty accurate though. My jet-ski has gps

 

This is a built-in safety. In several european countries the law states that the speedo can read more but Never less. So it's built into the system this way. BMW speedos are made to read optimistic some 3%.

 

In several european countries the law states that the speedo can read more but Never less. So it's built into the system this way.

This. Actually, the speedo can never read too slow, regardless of the wheel/tire option that could be fitted to a vehicle (without modification). But the car knows how far it has travelled. My VW had the sam issue.

 

Mine is spot on with gps and i've checked it with multiple gps units. I'm guessing it's because my 19s make up that 3% difference.

 

+1 for 2***8211;3 mph off being normal in BMWs. Both my 330i & my wife's X5 have "optimistic" speedometers when compared to GPS tracking (both have stock wheels). I just press the go pedal a little harder to compensate.

 

every one i have had has read high compared to the portable radar units the cops set up. i used to follow the new car reviews closely and noted that the speedometers usually read a bit high. maybe a car manufacturer would consider it a liability to report lower than actual speed. somebody somewhere would try to sue them for a speeding ticket or wreck. so i figured they would bump it up a little to be safe.

 

Mine reads 2mph+ as well. At almost any speed.

 

If you use the hidden OBC menu (choice 7.3 as it shows on my sig) you will notice that the digital reading is lower than the speedometer needle. The OBC menu is exact for speed.

 

interesting, very interesting.

 

The speedometer usually reads higher than actual speed by about 2-3mph because some sort of safety margin I'm assuming, but the point is it's not just your car, it's built into all of them to read this way.

 

OEM 18" it's spot on up to 200km/h

 

I would guess that possibly the European BMW's speedo's might be closer than the US/Canada spec cars?

But for everyone that has different size tires than OEM, if your speedo reads correctly, I would bet your mileage (distance covered) probably comes up short!

 

My e46 (stock wheels) is + 2 to 3 mph per GPS. Frankly it's very annoying.

My e36 was dead on; so is the household A6.

I consider is a flaw.

 

i kind of like it. keeps me out of trouble

 

Well i really should have searched - there's a ton of info out there, it seems pretty much all E46 have this problem and it's "normal" and that's with OEM wheel size, just like mine. Last night I checked it again, and it's only 1-2 mph off, not 2-3 like i thought earlier...a bit annoying, but guess better than other way around. All my other cars have been dead exact with GPS. must be a euro car thing, from what I read.
I guess I shouldn't depend much on the "range" or miles left indicator, either then...

 

My thoughts about speedometer inaccuracy

Just returning after a long absence on this forum...

Did anyone also realize that this speedometer inaccuracy also affects the odometer?

Just a 5% error can add about +500 bogus miles a year (assuming 10k/yr) to your odometer, thus lowering the value of your car... and if bought new, caused the warranty to lapse quicker.

Just saying...

 

Just returning after a long absence on this forum...

Did anyone also realize that this speedometer inaccuracy also affects the odometer?

Just a 5% error can add about +500 bogus miles a year (assuming 10k/yr) to your odometer, thus lowering the value of your car... and if bought new, caused the warranty to lapse quicker.

Just saying...

As stated before it is only on the needle. The ecu has the exact speed (as long as you dont have a drastically diffrerent OD on your tire.

 

My partner is always telling my to slow down on some of the heavily patrolled roads... and I keep replying "but the speedo is off!"

Why can't the needle just point to the actual speed??

 

My partner is always telling my to slow down on some of the heavily patrolled roads... and I keep replying "but the speedo is off!"

Why can't the needle just point to the actual speed??

Compensate with different sized rear tires. I replaced my 245's with 255's and my speed is spot on to my Garmin.

 

On my way to Vegas there was a little Honda driving next to me. I could clearly see their dash and it read 85 mine said about 91-92 now I know why people tailgate me when I'm going "70"

 

Hi. The only vehicle with a true speedo reading is a vehicle with a speedometer that has been calibrated. I drive a passenger coach and it has to go on a rolling road every two years for calibration. When I have my satnav on it shows the same speed as my speedo. Jim

 

M3 is even worse. Until I changed some of the coding in the cluster, it would read 80 when I was barely going 72

 

Hi TerraPhantm,

I know this is an old thread, but I'll try my luck.
I'm currently running 19" M3 wheels on my 323i. My odometer used to be 4Km/h above GPS speed, but now it's actually showing 97Km/h when I'm driving 100Km/h on GPS.

You mentioned changing some settings in the Cluster to fix this. Would you be so kind to tell me which values have to be changed exactly?

Thanks!

 

Speedometer accuracy

My 2002 330CI is the first car I have had where the speedo reads exactly the same as my Tom Tom. I've tried it in quite a few cars and the Tom Tom always says I am travelling slower than the speedo -typically 65mph at an indicated 70mph.I had decided that the Tom Tom was probaly wrong but the 330 speed ties up with the rev counter mph/1000 revs so I guess its right - I doubt it the speedo, rev counter and Tom Tom would all be wrong?