Speedometer error

T

Thork

Member
 Portland, OR
A few weekends ago, while on a long trip in a flat, long and very straigh expressway, I was curious to find how much is the error on my Zeddie speedometer, so I set the c/c to 100 mph and observed that the speep indicated on the GPS (Nuvi 660) was 96 mph, that would be a 4% error :!: I did the same "experiment" on my g/f car (MB 280C), same expressway, same GPS unit, similar wheather conditions and I got only 1 mph diference (c/c set @ 100mph gps indicated 99mph). Is that error a tipycal BMW feature, or is my speedometer out of wack? has any body else noted this?
 
I recently check my speedometer as well and with the c/c carefully set to 70 mph my gps was telling me 68 mph.
 
I noticed mine was 2mph off on me trip to Cali. I don't see it happening for most, but if you change your tire size yourself and don't update the computer to let it know there are different size tires on the car will be slightly inaccurate for a mph readout.
 
Don't most car have like a built in safety buffer on spedomeeter readings, always showing a bit more than the real speed?
 
My Origin B2 is about 2 or 3 mph below the indicated speed. I always figure it's handy, since it gives a bit of a buffer at a speed camera.
 
ive always thought mine was more like 9-10%.. so maybe i need to slow down a little more at speed cameras.. :S
 
All sorts of factors from tyre pressure, type of tyre, amount of tread remaining, play a significant factor in changing the true rolling radius of the tyre hence the indicated speed.

As mentioned above manufactures build in a margin to cover themselves and set high also flatters drivers and the perceived performance

Despite it being easy to get a 100% accurate reading in theoretical set ups in real world conditions it never will be.
 
I have read on many forums that BMWs typically have a 3 - 4% error which is a bit more than most cars. Hey, it's a good way for them to get the car out of the warranty period faster! :D :D
 
it's okay to read 2-4% higher which should be the case with most bmw's, but for instance my friend's Nissan SUV reads 8% higher (stock tires) so he was literally complaining to the dealership to extend his warranty by 8% and the guy started laughing :lol:
 
Sometimes the speed and the miliage indicator don't necessary go hand in hand. Anyone ever used their GPS to clock their odometer and see if the miliage is accurate or not?
 
Honestly, I haven't thought of that....but I want to say when I glanced at it on the return trip from Cali they were the same....
 
If you're valid/no wants and you're not a jerk, yea, I'm very reasonable. You know, I perfectly understand the need for speed :innocent:
 
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