Do the speedometers overestimate speed?

Vroomer said:
DHK said:
I don't have speed on my sat nav. Can it be programmed?
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Use to live in PR. Just test your speed going down the grade into SLO with that "YOUR SPEED IS" crap on the right. :wink:
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Nice! I'll do that. Thanks.
 
Just to add another piece of information, the wear on your tires may make a difference as well.

I just put new tires (factory spec sizes) on my 18" factory wheels and the speedometer wavered between being right on and 1 kilometer/hr optimistic at 100 km/hr compared to my Garmin.

I got the Garmin and the new tires over the winter, so I don't know what reading my worn out tires gave.

As these tires wear down I expect that the reading may change slightly as the revolutions/kilometer increase.

Bill
 
If you want to check without the use of GPS. There should be (in the UK) a Measured Mile in your area where the Police go to check their speedos. Just ask them where it is, it's perfectly legal. 60mph, 1 mile, 1 minute...simple
 
the speedo over estimating speed has been common knowledge since time began. When i drive my girlfriends VW is varies more than my Z, it depends from one manufacturer to the next. My dad's alfa is even worse, its miles out..
 
I think you could fairly ask that question about any car / vehicle.

Maybe being confident in my masculinity is something that I take for granted. Dunno.
 
I have found that my Z4 is much closer to the GOS speed of my Garmin Zumo than any of the other vehicles. It is consistently 2 mph slower than speedo indicated, my wife's Ford Escape is about 4 mph slower than indicated and my F-150 was about 5 mph slower than indicated. Those are all way better than my motorcycle (Triumph SprintST), it has a front wheel sensor and is consistently 10% off for any given speed so you get used to riding with the GPS as the speedo or doing a a 10% calculation (7mph difference @ 70mph).
 
I was running with my wife in her car yesterday.
She was going 80 and my car was showing 76
Just about 5% difference!
 
BMW's seem to have some of the most accurate speedo's in my experience.

Any of my old VAG cars seemed to be out beween 7-9%!! My VX220 was only ever 1mph out, probably due to its third party 'Stack' dash being somewhat more accurate!
 
I find my Z4 to be the most accurate speedo I've had in a production car. Of course it over reads, but only a little bit.
 
OK Flycaster....I've lost the plot...what is the actual message you're trying to get across? :headbang:
All speedos on all cars over-read, FACT..........they are designed to for safety, pure logic, end of story....and your point is? :poke:

Do the speedometers overestimate speed

If you look at your question.....overestimate....!
You make the assumption it is not accurate...thus it is an estimate, so it's going to OVER-READ, or UNDER-READ.....
Er.....better it over-reads isn't it, otherwise we'd all be in a mess :rofl: :rofl: :rofl:

Where is this argument going - sorry, but just cannot see it!

If your speedo is 'deadly' accurate at all speeds, I'd be a monkey's uncle!
The only thing that's accuarate is the fed's radar/laser gun.....and if your speedo under-reads, then bingo, you're not going to jail/gaol

Don't take this the wrong way, no flame wars please, but nope, I just don't get it!
Drive safely :D
 
Out of interest the speedo on my last car - TVR T350 was 100% accurate to the GPS up to 120mph, then it started to read over by 1-2mph. Until I tested it I always wondered why I was overtaking everything in sight cruising at the usual 85/90mph!

I agree that 99% of manufacturers ensure cars overread as underreading would have nasty consequences. Our MKV Golf GTi overreads by 5mph at 80. My old Audi A6 was similar.
 
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