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Discussion Starter · #1 ·
I don't understand how this could not be regulated some how? It would seem that there would be some law that the speed your speedometer says you are going is atleast fairly close to the true speed you are traveling at.
For instance 0-60 times could be manipulated if these claims I have been reading on Vortex are true. If I am going 60 mph, according to some posters I am only going about 55 or something??? So 0-60 time is a fraud???
This crap has got me wondering all of the time how fast I am really going? So can we somehow prove or disprove these accusations!!! And if it is true that our speedometers are not showing us our real speed, VW needs to fix it!!!
Unless all cars are reading FALSE info, then we would be equal. It would seem that some magazine would figure these inaccuracies out and uncover the lie if it were really true!!
Please put my mind at ease with this junk, and tell me VW and other car makers would not sale cars that are reading false info all of the time!!!!
Thanks, and oh yeah you thought you were going 80 on the way home tonight, but you were really going 45!!!!!! That is just stupid!!!



Modified by GPC777 at 11:53 PM 2-21-2006
 

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Re: Any real proof of the speedo inaccuracies on MKV GTI? (GPC777)

Laws/regs encourage manufacturers to calibrate the speedometers as they do. If a speedometer understated the speed, the manufacturer could face some big fines, and certainly some lawsuits. It would be much more difficult for a driver to win a lawsuit because a speedometer understated speed, particularly in the 5% margins most of us are seeing (odometers are usually right on). Think about it. With a 5% margin, the car says you are going 60, but you are really going 57. That doesn't seem like a whole lot.
Also, plus or minus-sizing tires can throw off the speedometer (and odometer) slightly (usually about a percent or so) since with the standardized aspect ratios being what they are, it isn't always possible to get an exact match on the circumference.
Magazines use meters measure speed to determine 0-60 times. It's not as if the driver just presses a stopwatch when the needle gets to 60.
 

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Re: Any real proof of the speedo inaccuracies on MKV GTI? (GPC777)

I don't know how many different cars you have owned, but all cars I have ever driven (enough to gauge the speed) were like that. It's probably not far-fetched to blame the litigious US society for this.
Actual speeds can vary depending on wheel size, tire manufacture, pressure, age, etc. Manufactures like to be a few percent on the save side, I think anything between say 3% and 8% or so is quite normal. For example, with a 5% error, if you are reading 60mph, you are really only going 57, reading 80mph you are only going 76, and so forth. While some people have reported a 10% error, I would find that excessive and would want the dealer to fix it.
It doesn't effect your mileage indication (total miles or mpg) in your MAF, though, and certainly doesn't effect factory claimed 0-60 times, which are not determined using the (or a standard) speedometer.
 

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Discussion Starter · #5 ·
Re: (placenta)

Come on man......I saw that post, I saw no real PROOF!!! I saw a few posters claiming on their car that they think with some device that they found some inaccuracy!! I want to know how this can happen if they are correct, and if it really does happen, do all other manufacturers do the same. I for one don't like to think that I have no clue how fast I'm really going, and it kind of upsets me that I just bought a brand new car with a speedometer that doesn't "REALLY" work! http://****************.com/smile/emthdown.gif
Please don't give me that SEARCH junk either, I stated in my original post that I was referencing what other posters had written!! I have been around these forums for over 5 years, and just because I don't spend my entire life posting on Vortex so that my sig will read 8 Billion posts, doesn't mean that I'm some moron that needs to learn how to search!!
If anyone has any real proof or insightful info, I would love to hear it!! http://****************.com/smile/emthup.gif Thanks and Peace.
 

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Discussion Starter · #6 ·
Re: Any real proof of the speedo inaccuracies on MKV GTI? (feels_road)

Thank you to the last two posters. Great info! So it seems that this is fairly normal. I have owned many, many cars, and I just took what I saw in the speedometer as the truth, as I'm sure most motorist do.
What I don't understand is how I've recieved speeding tickets before, going 80 in a 70, because the officer said I was going 11 or 12 MPH over the speed limit, if the car was really going 76 mph? To clarify, most officers and insurance companies won't mess with you or count a ticket if you were only going 9-10 MPH over, where I live.
I also understand the whole rim and tire diameter, etc, etc, I'm just surprised about this speedometer mess!! Thanks again, and Peace!!
 

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Re: (GPC777)

The way I determined it was by driving with my car on cruise control on the highway. In 15 minutes, I should have traveled 1/4 of the number of miles that my speedometer said (e.g. 15 miles if it were set to 60). However, according to the mile markers I went about 14.25 miles, hence about a 5% overstatement. This is an inexact measurement, since it depends on the accuracy of the mile markers and the state government, but my odometer corroborated as well.
 

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Re: Any real proof of the speedo inaccuracies on MKV GTI? (GPC777)

I traveled 70+ miles tonight on I-85 tonight in my 99 Passat. The odo and MFA moved in sync and were within 1% of the mile markers. After 70 miles of mile markers, the odo was 69.3 or 69.4 That's right at a 1% differential.
Then I set the cruise to 80, reset the MFA, which then showed an average speed of 76. Tried the same thing with cruise at 75 and 70. After resetting the MFA, it showed 71 and 67, respectively. I'm persuaded the MFA speed is within 1%. That puts the speedo error between 4% and 5%.
I think it's typical that speedometers are set on the high side.
 

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Re: Any real proof of the speedo inaccuracies on MKV GTI? (vwbaseball)

My B5.5 is within 1 or 2 %, but my MKIV Jetta, and now the MKV Jetta are in the 4/5 % neighborhood.
I just cruise @ 75 on the highway, and that is just enough over 70 to let everyone know that I am doing at least the speed limit, and at the same time keep the police on the side of the road.
Now if you want to discuss speedometers...
Heck Ford and Chevy don't even install them in the vehicles that they sell.



Modified by Tim Birney at 4:15 AM 2-22-2006
 

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Re: Any real proof of the speedo inaccuracies on MKV GTI? (Tim Birney)

why don't you just find an interstate highway, set the cruise control at a speed, and time how long it takes for you to travel a mile? seems like the easiest way to do this, and it takes all the guesswork out of whether or not your MFA is totally accurate too.
i've done this when i'm bored on long road trips, and the actual speed always came out pretty close to what the speedo read...maybe off by ~1mph or so. i repeated the test multiple times and avged the times.
 

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Re: Any real proof of the speedo inaccuracies on MKV GTI? (GPC777)

I use a GPS to calibrate the speedo. 100 indicated = ~92, 72 indicated = ~67, and so on....the faster you go, the greater the error.
 

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Re: Any real proof of the speedo inaccuracies on MKV GTI? (dangrass11)

Quote, originally posted by dangrass11 »
I use a GPS to calibrate the speedo. 100 indicated = ~92, 72 indicated = ~67, and so on....the faster you go, the greater the error.

Don't forget even the GPS used by civillians has a % error, how many statellites you pick up, clouds, overcast, etc.
No doubt the spedo is off by a few MPH but every car is, not really a big deal.
 

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yup,
I too used GPS to 'calibrate' my speedo.
no big deal. I know that when the speedo says 70, I'm doing ~ 67.
when it says ~74, I'm doing ~ 70.
also, it's not like the car has a digital speedo and you set your speed at EXACTLY 55 mph, you're just looking at a rough gauge that sits somewhere around 55 mph...
but remember, DO not try to 'speed' by your speedometer reading on a driving test and then tell the bmv person that you're just compensating for the speedometer being off

That won't work.......
and remember, everything has a percent error, civi gps, military gps, gti's speedometers, mile markers, radar guns, speed strips, etc......
 

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Re: (rmb6-2)

Quote, originally posted by rmb6-2 »
yup,
I too used GPS to 'calibrate' my speedo.
no big deal. I know that when the speedo says 70, I'm doing ~ 67.
when it says ~74, I'm doing ~ 70.
also, it's not like the car has a digital speedo and you set your speed at EXACTLY 55 mph, you're just looking at a rough gauge that sits somewhere around 55 mph...
but remember, DO not try to 'speed' by your speedometer reading on a driving test and then tell the bmv person that you're just compensating for the speedometer being off

That won't work.......
and remember, everything has a percent error, civi gps, military gps, gti's speedometers, mile markers, radar guns, speed strips, etc......

Exactly, car spedo's are not designed to be accurate within .001% error . Even if it were you would have to calibrate it every so often to maintain it. We have a peice of equipment that measures the loss in dB of fiber optic cable, it has to be calibrated every month to retain the precision we need. That's not resonable with a car spedo. It approximates speed which is good enough.
 

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So, the question is... Is the OP satisfied with these answers?

As I've said in the past, my MKIV is off by 3-4mph when doing 75mph. The MKV is off by 5-7 at the same speed. It is a bit annoying that the MKV is that much more, but I know nothing can be done to "fix" it, and as time has moved on so has my bitterness towards it. No big deal, as all German cars are like this, and many other makes as well.
 

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The speed pulse wire sends the correct vehicle speed to the insturment cluster. Which I believe is also to make sure the odometer is accurate.
Since my D1 nav system is hooked into this wire and has a "vehicle dynamics" display which includes a speedo I can tell you with certanity that the D1 speedo and the cars speedo differ in their readings.
The Pioneer one is quite accurate while the car speedo is not. By the same margin of error posted here.
 

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Re: (thread)

i've also noticed that the speed warning in my MFA isn't exactly in tune with my speedo. i set my speed warning at 75mph, and it usually doesn't pop up until it looks like i've hit 76 or 77 on the speedo.
 
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