Spedometer inaccuracy? - Toyota Yaris Forums

otterhere · 11-24-2008, 02:41 PM

Mentioned in another thread:

I'd swear my spedometer shows me going 10-20 miles faster than I'm actually going; has anyone else noticed this, or should I report it to my dealer??? Not sure how to measure this accurately except that yesterday I was just moving with the flow of traffic on the interstate (70 mph; most do 75-80 mph), and it showed me doing 90!!! Not everyone else was also driving a Yaris, either...

contraband831 · 11-24-2008, 03:15 PM

Mine is off by about 5mph, i noticed it with my GPS, but i don't mind.

tetzyamis · 11-24-2008, 03:52 PM

Tire size will make the speedo off, but not that much off.
Let's say your original tire size is 185/60/15, to make the speedo off by 10 mph at 60 mph, you gotta put tires like 165/50/14.
I don't think tires that small even exist.

I would ask a friend to drive next to you and ask him how fast he's going.
If your speedo is off, then I'd take it to the dealer.

otterhere · 11-24-2008, 04:38 PM

They do substitute 15" wheels for the original 14" when they add the packages (I got convenience and all-weather, only because I couldn't avoid them)... Could that be it?

tetzyamis · 11-24-2008, 04:52 PM

Quote:

Originally Posted by otterhere

They do substitute 15" wheels for the original 14" when they add the packages (I got convenience and all-weather, only because I couldn't avoid them)... Could that be it?

No, that will make the speedo slower, not faster.
If 175/65/14 says 50 mph, 185/60/15 would say 48.35 mph.

nemelek · 11-24-2008, 05:23 PM

Making the asssumption that the speedometer and the odometer are linked together, the odometer is easy to check using the highway mile markers.

CKaelin · 11-24-2008, 05:32 PM

According to my scan guage my spedo is pretty much dead on. Maybe a mile per hour fast.

WeeYari · 11-24-2008, 05:38 PM

Quote:

Originally Posted by nemelek

Making the asssumption that the speedometer and the odometer are linked together, the odometer is easy to check using the highway mile markers.

Just as easy for speedo too. Hold constant speed between markers and time it.

CTScott · 11-24-2008, 05:40 PM

Quote:

Originally Posted by CKaelin

According to my scan guage my spedo is pretty much dead on. Maybe a mile per hour fast.

The speedometer and scanguage get their data from the same place. The Yaris' speedo is purely electronic. If you see a difference between the speedo and the SG, it is because of the SG's lag in reading and displaying data from the OBD port.

voodoo22 · 11-24-2008, 09:20 PM

Speedometers on all cars are set to read faster than you are really going, and that's correct. Putting on 15 inchers in place of 14's would make your speedometer read about 3-5% slower depending on overall dimensions.

b_hickman11 · 11-24-2008, 09:33 PM

It doesnt matter if you have the 14's or the 15's. If it came from the factory then the speedometer is set using the rims on it. I had a 05 Taco with factory 20's which was an upgrade. The regular rim size was 17. My speedometer was set for the 20's.

tetzyamis · 11-24-2008, 10:03 PM

Quote:

Originally Posted by PK198105

it does matter , if the dealer doesn't reset the ecu. if you change your overall diameter the speedo will be off.

Hickman said "If it came from the factory", which means dealer did not change the rim.

TinyGiant · 11-24-2008, 10:13 PM

i'm about 5mph off with the summer tire/rims

ddongbap · 11-25-2008, 03:57 AM

Are you guys taking into consideration the overall diameter of the rubber themselves? It really doesn't matter how much off the metal rims are.

IllusionX · 11-25-2008, 10:04 AM

Quote:

Originally Posted by PK198105

yes but if downgraded after to 17's without resetting the ecu the speedo would be wrong

No. It doesn't change a thing. A sales guy at Brossard Toyota (he doesn't work there anymore) did the test with 2 echos. a hatchback with factory 14" (175/65R14) and a sedan with factory 15" (185/60R15). They did many tests driving side by side... both at 100kmh, the 15" would over take the 14". The sedan would have to drive at 96kmh to stay equal with the hatch, and the hatch has to drive at 104kmh to keep up with the sedan.
The test was done to prove that toyota did not adjust the ECU to reflect the different overall diameter size of the wheel/tire.
In fact, to match the 175/65R14, you would need 185/55R15.

Bob_VT · 11-25-2008, 10:08 AM

Mine is quite accurate.

GPS, Speedometer and SCII all show exactly the same mph. I have noticed that the GPS unit has a lag in the reading.

I am running stock tires on steelies.

otterhere · 11-25-2008, 10:15 AM

Wow, y'all have given me a headache; did I mention that I'm math-challenged??? It doesn't bother me; I just move with the flow of traffic anyway, keeping a safe distance behind whoever's in front of me.

Certainly not going to take it back to the dealer and complain; too happy.

floydisrock · 11-25-2008, 10:31 AM

Math is easy--> http://www.discounttire.com/dtcs/infoTireMath.dos

11-24-2008, 02:41 PM	#1
otterhere Drives: 2008 Yaris 3-door Meteorite Join Date: Oct 2008 Location: Southeast Posts: 398	Spedometer inaccuracy? Mentioned in another thread: I'd swear my spedometer shows me going 10-20 miles faster than I'm actually going; has anyone else noticed this, or should I report it to my dealer??? Not sure how to measure this accurately except that yesterday I was just moving with the flow of traffic on the interstate (70 mph; most do 75-80 mph), and it showed me doing 90!!! Not everyone else was also driving a Yaris, either...

11-24-2008, 03:15 PM	#2
contraband831 El Huevo Drives: 2007 Liftback Join Date: Aug 2006 Location: CEN*CAL Posts: 959	Mine is off by about 5mph, i noticed it with my GPS, but i don't mind. __________________

11-24-2008, 03:52 PM	#3
tetzyamis '09 5dr Drives: 2009 Yaris 5-Door Bayou Blue Join Date: Oct 2008 Location: HI Posts: 238	Tire size will make the speedo off, but not that much off. Let's say your original tire size is 185/60/15, to make the speedo off by 10 mph at 60 mph, you gotta put tires like 165/50/14. I don't think tires that small even exist. I would ask a friend to drive next to you and ask him how fast he's going. If your speedo is off, then I'd take it to the dealer. __________________ 2009 5-Door Yaris LB Bayou Blue Pearl 2009 5-Door Yaris LB Black Sand Pearl

11-24-2008, 05:23 PM	#6
nemelek DWEED Drives: 3DR 2008 Metorite Metalic Join Date: Oct 2008 Location: Arizona Posts: 1,161	Making the asssumption that the speedometer and the odometer are linked together, the odometer is easy to check using the highway mile markers. __________________ Making a decision without following it with an action is still a fantasy.

11-24-2008, 05:32 PM	#7
CKaelin Drives: 2008 Yaris LB 5 speed Join Date: Oct 2008 Location: Boxborough, MA Posts: 140	According to my scan guage my spedo is pretty much dead on. Maybe a mile per hour fast. __________________ My other ride's a Gixxer!

11-24-2008, 04:38 PM	#4
otterhere Drives: 2008 Yaris 3-door Meteorite Join Date: Oct 2008 Location: Southeast Posts: 398	They do substitute 15" wheels for the original 14" when they add the packages (I got convenience and all-weather, only because I couldn't avoid them)... Could that be it?

11-24-2008, 09:20 PM	#10
voodoo22 Drives: Yaris Sedan (auto) Join Date: Jun 2007 Location: Toronto, Ontario Posts: 545	Speedometers on all cars are set to read faster than you are really going, and that's correct. Putting on 15 inchers in place of 14's would make your speedometer read about 3-5% slower depending on overall dimensions.

11-24-2008, 09:33 PM	#11
b_hickman11 Drives: 08 Sedan Join Date: Oct 2008 Location: Tyler, TX Posts: 899	It doesnt matter if you have the 14's or the 15's. If it came from the factory then the speedometer is set using the rims on it. I had a 05 Taco with factory 20's which was an upgrade. The regular rim size was 17. My speedometer was set for the 20's.

11-24-2008, 10:13 PM	#13
TinyGiant Tiny Giant Clothing View User's Garage Drives: 2008 Blazing Blue Yaris 3D LB Join Date: Oct 2008 Location: Rochester, NH Posts: 3,394	i'm about 5mph off with the summer tire/rims __________________ Sold the yaris... rocking an 89 vw cabriolet now :)

11-25-2008, 03:57 AM	#14
ddongbap Banned Drives: yw calls me douche and racist. Join Date: Aug 2007 Location: hay Posts: 2,183	Are you guys taking into consideration the overall diameter of the rubber themselves? It really doesn't matter how much off the metal rims are.

11-25-2008, 10:08 AM	#16
Bob_VT View User's Garage Drives: 08 Yaris LB Join Date: Oct 2008 Location: Vermont Posts: 1,704	Mine is quite accurate. GPS, Speedometer and SCII all show exactly the same mph. I have noticed that the GPS unit has a lag in the reading. I am running stock tires on steelies. __________________ some people are little slinkies. . . . .they are really good for nothing. . . .but they still bring a smile to your face when you push them down a flight of stairs. Come to the DARKSIDE..... We have candy

11-25-2008, 10:15 AM	#17
otterhere Drives: 2008 Yaris 3-door Meteorite Join Date: Oct 2008 Location: Southeast Posts: 398	Wow, y'all have given me a headache; did I mention that I'm math-challenged??? It doesn't bother me; I just move with the flow of traffic anyway, keeping a safe distance behind whoever's in front of me. Certainly not going to take it back to the dealer and complain; too happy.

11-25-2008, 10:31 AM	#18
floydisrock 73 Centurion droptop 455 Drives: 2009 S Sedan Join Date: Oct 2008 Location: Phoenix Arizona Posts: 64	Math is easy--> http://www.discounttire.com/dtcs/infoTireMath.dos __________________ "THIS SITE HAS BEEN HACKED BY www.bimmerfest.com. YOU FUCKERS!"