bmw lies

[bimmerdude]

I just found out something interesting about our bmws from the US bimmer forums' FAQ section:"Q: My speedometer reports a higher speed reading than my GPS (or the radar of the cop who pulled me over, not that I am complaining...). Is there something wrong with my car? Does that affect my odometer or service readings?A: BMW over-reports the speed at which you traveling (typically 3-5mph or 4-8km/hr depending on speed). This is an intentional correction by BMW and only affects your speedometer reading and cruise control speed setting. Everything else including odometer, mpg reading and service readings are accurate and unadjusted. "Now i know why that cop never pulled me over

 

[seech]

bimmerdude, if i'm not mistaken, all car manufacturers have speedos which is higher than the actual speed itself. apparently this is for legal reasons (imagine if it is lower than your actual speed and you get saman etc. etc.). The only one that was accurate was for the McLaren F1 which was spot on when tested by Autocar.

Best way to test is to measure the km marker post when on the highway. If you are travelling at 120kmh, 1 km would take 30 seconds. So far most of the cars that I have driven under report by around 10 kmh. Changing rims and tires also alters the rolling radius of the tires and will have an effect on actual and reported speeds. Before I changed to 17" mine was around 10kmh lower. Changed to 225/45 was around 5km, now with 235/45 its accurate.

Don't agree with the answer given that odometer, mpg, etc are not effected. What rubbish. My fuel consumption has 'dropped' as I now cover less reported km due to the tire size difference.

Just my 2 sen.

 

[bimmerdude]

i disagree. this is not the simple 'inaccurate reading' that you are referring to. changing the rims wont affect the 'margin' that bmw intentionally program into the speedo. this is what i understand. to confirm, if u have a gps, try to check? I may be wrong.

 

[loafer]

Seech is right actually. Changing the rims and tire size does affect the reading of your speedometer.

http://www.csgnetwork.com/speedocalibcalc.html

 

[zamrulesz]

agreed.... not just bmw

 

[fabianyee]

please first understand how the car gets its speed reading... It gets the reading from the pulse generator at the rear differential.... This has been the way for all BMWs for the past 20 years. i believed this is still the same for the current models. It calculates the number of rotation per sec/minute of the driveshaft (output flange), then the speedometer would translate that to its speedo reading based on the stock tyre size hardcoded into the calibration..

So if you change the tyre size which has a LARGER diameter or circumferrence, it would definitely affect the speedo reading. And it doesn't have a second system to read the speed, unless it uses the in-car GPS system to countercheck the reading...

And yes, almost all manufacturer built in higher speed reading between 5-10kph...

 

[WMB23]

wow good news! that mean v can tekan minyak kuat kuat lah! Good info

 

[bimmerdude]

please first understand how the car gets its speed reading... It gets the reading from the pulse generator at the rear differential.... This has been the way for all BMWs for the past 20 years. i believed this is still the same for the current models. It calculates the number of rotation per sec/minute of the driveshaft (output flange), then the speedometer would translate that to its speedo reading based on the stock tyre size hardcoded into the calibration..

So if you change the tyre size which has a LARGER diameter or circumferrence, it would definitely affect the speedo reading. And it doesn't have a second system to read the speed, unless it uses the in-car GPS system to countercheck the reading...

And yes, almost all manufacturer built in higher speed reading between 5-10kph...

Yes i agree that changing rims or tires from stock will affect the reading. what i have been saying is that bmw builds in a plus factor into their speedo readings. so it doesnt matter if ur tires or rims are not stock. u will still get a plus factor. this is what i understand from the original posting i quoted.

 

[pussy]

the best is you can the kerinchi flyover where there is a speed indicator on the speed you are travelling...

mine is 5kp/h difference..

 

[astroboy]

Aiyaa.. even the thickness of the remaining tread and the tyre air pressure play a role in determining the rolling circumference of the tyres.

So just take the speedo and odo reading with few percent tolerance and you'll be fine. Stop worrying too much.