Speedometer giving false reading

<div class='quotetop'>QUOTE(Paul B @ Aug 17 2007, 05:58 PM) [snapback]497691[/snapback]</div>

The speedometer dispaly is intentionally biased to meet "UN-ECE Regulation No. 39".
http://www.unece.org/trans/main/wp29/wp29regs/39rv1e.pdf

Ken@Japan

 

<div class='quotetop'>QUOTE(ken1784 @ Aug 17 2007, 07:17 PM) [snapback]497693[/snapback]</div>

Wow! Thanks for the info, Ken. Just goes to show that we not only get stuffed around by our various governments and their departments, even the UN gets in to make life difficult.

 

<div class='quotetop'>QUOTE(Paul B @ Aug 17 2007, 03:58 AM) [snapback]497691[/snapback]</div>

Hi Paul,

Mine also reads about 10% fast, In the UK this is normal its just having the digital speedo you see it more and also with sat-navs you see the real speed. You just have to note that a number of important speeds on the prius have to be converted to UK speed. The ICE starts at 44mph not 41mph as will be stated by none UK owners.

As regards to the mileometer I would assume that is correct and does not have the 10% error.

Gary

 

<div class='quotetop'>QUOTE(AussieOwner @ Aug 17 2007, 06:46 AM) [snapback]497703[/snapback]</div>

You could put new tires on with a different Revs/Mile. For the USA, the standard tire is supposed to be 855 RPM, at least when new. As the tire wears, RPM goes up and apparent speed & mileage increases.

You want the speedometer and odometer to be lower, so get a tire size that is 8 to 10% larger. Look up the specs on whatever tires you have now at either the manufacturer's web site or a place like tirerack.com.

- Tom

 

<div class='quotetop'>QUOTE(Tom_06 @ Aug 17 2007, 06:02 AM) [snapback]497708[/snapback]</div>

In the UK only the speedo will read fast by design for "saftey" and so there is no doubt that you are exceeding the speed limit. The miles traveled are accurate. The speed is shown different on the Scangauge but the miles traveled are the same.

 

As some have already posted, cars are required to show the speed with a margin of error. If you had for instance a ScanGaugeII, you would see that the car deep down within knows the true speed (or at least very close to it).

But I'm surprised to hear of 10% off. My current car (a 2005 Peugeot 1007) is about 4-5% off, which I thought was the norm. Since 10% off is the limit for the UN regulations (in Norway at least, a new car is illegal to sell if it's speedometer is more than 10% optimistic), Toyota seems to have gone very close to the limit.

I remember reading a tread here or on PriusOnline where a Swede had checked his speedometer from 0 to 170kph, finding that the speedometer seemed to have 3 steps of "error". The faster you drive, the bigger difference between displayed speed and true speed. Sadly, I cannot find that posting tight now, but I'll try to find it.

EDIT: Here is the thread. Post #26 has the results from the Swedish jury: http://priuschat.com/index.php?showtopic=30709&st=0

Stein

 

My motorbike has a 11% error in the speed reading but less than 1% error in the odometer.
I haven't noticed this with my Prius, will check it against my GPS.

 

<div class='quotetop'>QUOTE(Paul B @ Aug 17 2007, 11:50 PM) [snapback]497802[/snapback]</div>

Hi Paul,

Please be aware that a dealer or any car manufacturers can't adjust it unless the speedometer reading is out of range from the regulation.

Ken@Japan

 

Man, mine is like 1-1.5MPH above my speed at 45MPH, so that's 2-3% off, and my tires are nearly worn all the way down. I'm actually putting on some slightly, like 10-15 more revs per mile, tires than the stock ones. I'm tying to get some of that mileage back. I've already gone past the warranty on the Potenzas by 66%, 50k+ miles on a 30k warranty. I figured that was about as good as it was gonna get.

I thought mine was pretty far off, but considering my tires were worn I wasn't too concerned. I'd be pissed knowing that my speed was 10% off.

 

<div class='quotetop'>QUOTE(Alexstarfire @ Aug 17 2007, 12:46 PM) [snapback]497889[/snapback]</div>

According to my GPS the speedo is off 1mph at most. This was observed across PA, OH & IN.

 

The Japanese 2004 Prius has +6km/h offset to meet the regulation. 10% off at 60km/h.
But, our 2005 or later models has only +3km/h offset. 5% off at 60km/h.
Anyway, both readings are within the regulation.

Ken@Japan

 

One of the first things I liked about the Prius was the accuracy of the digital speedometer. There are a lot of digital speed check signs where I drive, and my Prius speed is exactly the sign speed, playing with it on numerous different occasions to test it. Not even one mph off, can I detect. This is with the new original tires. I would guess all Prii are built exactly the same.

 

My GPS shows about 2 mph off.

 

My GPS shows 69 mph when the speedometer shows 70 mph. Sounds close enough to me.

 

My standard U.S. Prius (non-touring) reads one digit high, which is normal for digital speed displays. For example, if my speedometer shows 55 mph, I am actually going 54 mph, which is pretty darned close to perfect. I may have gained a little accuracy when I switched the tires to Micheline MXV4+ Energies in the stock size.

Tom

 

Hi Ken,

Are you implying that a dealer "could" adjust the speedometer if need be? Previous posters (perhaps uninformed) have indicated it is impossible to adjust the speedometer in any way.

It seems deceitful of Toyota to intentionally have the speedometers so off calibration. Most consumers are most likely unaware of this and assume their fuel mileage is greater than reality and it also hurts resale value as the odometer will read higher than actual miles traveled. May also be a profit generator for the dealers as the consumer will take the vehicle in for service more often than needed.

It seems that it would be very simple and inexpensive for automakers to couple the speedometer and odometer with a simple GPS chip to give priority to the GPS speed and mileage data when a satellite signal is available. Maybe some autos already do this.


Rick
#4 2006

 

My Prius speedometer consistently reads 3% higher than the GPS, on level ground.

Note that when you do GPS comparisons, you need to be on level ground. The GPS gives you 2D velocity, as if you are on level ground, whether or not you really are. (If you drop a GPS down a mine shaft, it will read zero mph -- until it hits the bottom.)

Your speedometer on the other hand gives you your velocity along whatever slope you're on (as long as your tires are not slipping or skidding). Driving on a one degree slope, up or down, will result in a perfect speedometer reading 1.75% faster than a perfect GPS.

In theory a GPS could compute 3D velocity since they compute a 3D fix (actually 4D including time). However they are much less accurate in the vertical direction than in the two horizontal directions, especially when moving. I use a GPS when flying, and the thing does try to estimate climb and descent rates with the 3D fix. However its not very accurate compared to the standard air-pressure driven vertical speed indicator.