Speedometer giving false reading

alexstarfire · 08-17-2007, 12:46 PM

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.

JimN · 08-17-2007, 10:15 PM

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

Quote:

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.
[/b]

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

bramwell · 08-18-2007, 01:59 PM

It's starting to look as though this is a european issue.

Anyone in the States have the same problem i.e. 10% higher reading than actual speed ?

Paul.

ken1784 · 08-18-2007, 03:15 PM

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

Mr.Vanvandenburg · 08-19-2007, 12:32 AM

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.

lenjack · 08-19-2007, 09:20 AM

My GPS shows about 2 mph off.

Skinflint · 09-14-2007, 09:14 AM

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

qbee42 · 09-14-2007, 09:48 AM

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

viking31 · 09-14-2007, 09:50 AM

Quote:

Originally Posted by ken1784 @ Aug 17 2007, 12:05 PM) [snapback

497854[/snapback]</div>

Quote:

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

<div class='quotemain'>
It's a shame that there is not an adjustment that can be made by the dealer.

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
[/b]

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

madler · 09-14-2007, 01:00 PM

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.

08-17-2007, 12:46 PM	#11
alexstarfire Join Date: Feb 2007 Posts: 218 My Car: Package: Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	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. __________________ Not bad for a Classic Prius.

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Speedometer and mpg reading is off	saechaka	Prius Main Forum	21	12-29-2007 08:46 PM
GE giving away Prius	g-man430	Prius Main Forum	0	10-25-2006 04:28 PM
Giving Thanks for Prii	Tempus	Prius Main Forum	1	11-24-2004 02:19 PM
Giving Up	Hoodwink	Prius Main Forum	10	02-12-2004 01:53 PM

08-18-2007, 01:59 PM	#13
bramwell Join Date: Aug 2007 Posts: 3 My Car: Package: Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	It's starting to look as though this is a european issue. Anyone in the States have the same problem i.e. 10% higher reading than actual speed ? Paul.

08-18-2007, 03:15 PM	#14
ken1784 SuperMID designer Join Date: Dec 2003 Location: Yokohama, JAPAN Posts: 1,384 My Car: 2004 Prius Package: G Touring Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 3	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

08-19-2007, 12:32 AM	#15
Mr.Vanvandenburg Senior Member Join Date: Mar 2007 Posts: 130 My Car: Package: Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	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.

08-19-2007, 09:20 AM	#16
lenjack Senior Member Join Date: Dec 2006 Location: Pennsylvania USA Posts: 332 My Car: 2007 Prius Package: #5 Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	My GPS shows about 2 mph off.

09-14-2007, 09:14 AM	#17
Skinflint Join Date: Jul 2007 Posts: 6 My Car: Package: Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	My GPS shows 69 mph when the speedometer shows 70 mph. Sounds close enough to me. :P

09-14-2007, 09:48 AM	#18
qbee42 Senior Member Join Date: Mar 2006 Location: Northern Michigan Posts: 5,643 My Car: 2006 Prius Package: #7 Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 6	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

09-14-2007, 01:00 PM	#20
madler Senior Member Join Date: Apr 2005 Location: Pasadena, California Posts: 269 My Car: 2005 Prius Package: #4 Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	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.