Spedometer accuracy

[harryd14]

so i was driving around my campus the other night, and they have those speed signs up everywhere that show have fast you are driving so i decided to see how accurate they were comapared to what my spedometer showed. And after driving by with it set on cruise at 35mph, the display board only read 32mph... i was wondering if this was just the sign that was wrong or if the spedometer was actually not calibrated properly? i figured it was probably the machine but you never know... just wondering if anybody else had noticed this and tried testing it against something more accurate

[LampyB]

those signs are way off all the time...

[tike0rz]

I've heard VW does that out of the factory, but not recognizable at low speeds like 32mph. Prolly the display was configured to be generous.

[Rothie]

My GPS list the speed that I am traveling. I have used it in several different cars and my 2008 A4 was always about 5 mph under what the speedometer was showing.

[agorich]

weak. no wonder everyone still zips past me when i'm on the highway!

[lnferno]

Yeah, I've tested this quite a few times with my GPS. I can be going 60 MPH, but my speedo will say 62-63 MPH.

[ggg20t]

haha im happy this thread came up. I was on the highway coming home from work going 65 miles per hour and that stupid speed sign said 62. I was all worried, called my dealer and they pretty much told me that i am retarded

[NorcalPB]

Just a side note, even though your speedometers are off by a couple mph, your mileage is exact as the car knows how fast its going even though its lying to you....

[bcramer]

I have yet to find a car that doesn't over read the mph on the speedo. It's a way for the manufacturer to CYA in the event anything ever happened.

[brownishwater]

^^^
hes right. All cars usually read 1 or 2 mph under the actual speed, but in our case (Audi's, B7 atleast) read 3 mph under the actual speed...i have used my cop friend's rader gun to test. I made several runs and each time, the speed on my speedo was 3 mph over the speed that the radar gun was clocking

[Pete4 1.8t]

All VAG products have speedos that under read by 3 MPH. It's just their selected buffer zone so they don't have to worry about any stupid lawsuits and to an extent it's a safety feature. Nothings wrong, all of our Audi's and any other one's I've driven under read by 3 MPH

[Blarg]

I have a gps speed application on my iPhone and checked my speed on the highway and the speed was right on with maybe a 1 mph difference.

[ecks618]

I went to the dealer with the same problem, my speedometer is about 3-5 miles off consistently (Shows higher than speed). According to them as long as its within 10% it is considered "good enough"(Quoted Audi of Manhattan technician)

[Blarg]

Wow, 10%!!

[Entropy333]

Yeah, I've tested this quite a few times with my GPS. I can be going 60 MPH, but my speedo will say 62-63 MPH.

+1

[volcomic]

I have a gps speed application on my iPhone and checked my speed on the highway and the speed was right on with maybe a 1 mph difference.

It's not actually GPS so it's not nearly as accurate...

[Sanjman]

Are you sure it isn't the accelerometer that is measuring your speed on your iPhone?

Anyways... http://www.chickjunk.com/how-does-th...motorcar-work/

If you understand how the speedo works, you will see why it isn't the same for people. Besides that, your wheels/tires combo can make it a littler more inaccurate as well. I believe in some countries it is 10% tolerance by law... can't figure it out in the USofA.

[Alecd90]

my 9500i radar actually displays 1mph slower then what my spedo reads

[johntesi]

In the US it is either 6% or 8%. Definitely not 10. At least, that's what I've heard... Not trying to spread heresy, I just can't remember if it was 6 or 8. It may vary by state legislation.

[Lewie06A4]

According to my GPS, when traveling at 55mph on the speedo, the GPS said 54, and at 75 on the speedo, gps said 73. By far pretty accurate.

[RedS-line]

those speed signs are usually off by a couple of mph. my speedometer is always off by 2-3mph. this is the way it is

[BLACKa4QUAT]

yeah i agree with the whole speedo being off by about 2-3 mph, tested by those your speed is : things and gps unit

[john@fifteen52]

Yeah, I've tested this quite a few times with my GPS. I can be going 60 MPH, but my speedo will say 62-63 MPH.

My 06 A4 also reads about 5% high compared to Garmin GPS. Here are some other cars i checked with the Garmin:

04 allroad - accurate
02 S6 - accurate
06 Jetta - reads high 5%
06 GTI - reads high 5%
99 Cabrio - accurate
04 Honda Pilot - accurate
02 Merc ML500 - reads high 8%
00 A6 4.2 - reads high 5%

All with the same Garmin Nuvi unit. Although I don't swear the GPS is 100% accurate, it is very consistant with speed.

I like the fact that it gives me a little room for error if I run a little faster than I should and go through a speed trap.

The downside, the speedometer and odometer run off the same sensor signal. If it says you are going 5% faster than actual, you are also adding 5% to the odometer that isn't there.

[Blarg]

It's not actually GPS so it's not nearly as accurate...

I have the iPhone 3G so it is real GPS but I would say it's the program that isn't accurate.

I'm happy the car is off a little so I think I'm going faster than I really am!

[eMacPaul]

I wonder how much of this is just due to tires having worn down tread? If you've lost half an inch of tread all the way around on a 25" tire, that's a 4% difference.

[Quattro4mage]

The speedometer accuracy is due to ECE Transport Regulation 29 as amended in 2000. This is an European Union regulation meant to establish speedometer standards for motorized vehicles in the EU.

Google the regulation and bore yourself to death on how manufacturers have to have speeedometers read faster than the actual vehicle speed in the EU.

BTW, there is no VAG-COM adjustments for speedo accuracy and your odometer is not affected.

[RedS-line]

^thats good to hear that we re not getting screwed on our odometers (warranty) because of our fast speedos.