Speedometer - Toyota Yaris Forums

david.gartee1 · 07-13-2011, 09:57 PM

I recently installed a new HU that I had in my previous car. It is a nav unit that uses the VSS to show me on-screen the speed, g's, and all that. Well, the HU seems off from the speedometer by about 5-10% (haven't really done the math). I thought it might have something to do with the wire not being connected correctly. Even more recently, I downloaded an app to my Android phone that shows the MPH using the internal accelerometer and GPS, and the two are very close to the same.

I was not told when I purchased the car that there have been any mods done to the wheels, transmission, or anything that would case the discrepancy. Does anyone know what I should look for to find out, or should I just believe the speedo? If it is wrong, that means that the trip meter, odometer, and everything else is incorrect, also. I'm hoping that is not the case. And before anybody asks, no I have not yet driven with someone following me to see if they have the same speed. I will do that some time and post an update, but I would like to know what other people on here think in the meantime. TIA

Lil Abner · 07-13-2011, 10:23 PM

Which are very close? The Headunit and Android phone? Factory speedometers can be off by several percent just due to tire sizes. 14" rims and 15" rims use slightly different tire diameters (the outer diameter). If the previous owner changed tires, there's also the chance the tires of slightly larger or smaller. What size tires does the car have currently? Oh, and on my 2009, my Scangauge and GPS read the same, the speedometer on the dash is off by about 1-2mph at 60mph.

david.gartee1 · 07-13-2011, 11:24 PM

Sorry, the Android app and the HU are very close. My tires are 185/60r15 made by GoodRide. It looks as if the wheels are the factory steelies.

Lil Abner · 07-14-2011, 09:14 AM

Honestly, I think your Android and HU are correct, the car is a bit off. But yours is just like mine. The tires are within the factory spec, so you're good there. The needle isn't adjustable, so you're basically stuck. But the majority of cars have the speedo off by a little bit. I'd say just get use to it. Like I said, for me, I can set my cruise at "60", but I'm actually doing 57-58.

Kiteless · 07-14-2011, 06:13 PM

Quote:

Originally Posted by Lil Abner

Honestly, I think your Android and HU are correct, the car is a bit off. But yours is just like mine. The tires are within the factory spec, so you're good there. The needle isn't adjustable, so you're basically stuck. But the majority of cars have the speedo off by a little bit. I'd say just get use to it. Like I said, for me, I can set my cruise at "60", but I'm actually doing 57-58.

If I go 65MPH on the odo, GPS says I am going 61mph. Mine are stock 14" steelies. So I go 70mph on the freeway and that gets me like 66mph or so.

david.gartee1 · 07-15-2011, 02:32 AM

Wow, mine is the same way. That just does not seem right. Over the life of the car, that could mean the real mileage is off by thousands. Not to mention the true MPG. I like to know that I can look at my speedo and know my real speed. Seems to me like Toyota should do something about this. I was cruising down the interstate at "80" tonight, and my GPS said 74.5-ish. To me, that is a problem.

07-13-2011, 09:57 PM	#1
david.gartee1 Drives: 2007 Yaris HB Join Date: May 2011 Location: Columbia, TN Posts: 7	Speedometer I recently installed a new HU that I had in my previous car. It is a nav unit that uses the VSS to show me on-screen the speed, g's, and all that. Well, the HU seems off from the speedometer by about 5-10% (haven't really done the math). I thought it might have something to do with the wire not being connected correctly. Even more recently, I downloaded an app to my Android phone that shows the MPH using the internal accelerometer and GPS, and the two are very close to the same. I was not told when I purchased the car that there have been any mods done to the wheels, transmission, or anything that would case the discrepancy. Does anyone know what I should look for to find out, or should I just believe the speedo? If it is wrong, that means that the trip meter, odometer, and everything else is incorrect, also. I'm hoping that is not the case. And before anybody asks, no I have not yet driven with someone following me to see if they have the same speed. I will do that some time and post an update, but I would like to know what other people on here think in the meantime. TIA

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07-13-2011, 10:23 PM	#2
Lil Abner Drives: 2009 3dr LB Manual Join Date: Mar 2010 Location: Dublin, Ohio Posts: 412	Which are very close? The Headunit and Android phone? Factory speedometers can be off by several percent just due to tire sizes. 14" rims and 15" rims use slightly different tire diameters (the outer diameter). If the previous owner changed tires, there's also the chance the tires of slightly larger or smaller. What size tires does the car have currently? Oh, and on my 2009, my Scangauge and GPS read the same, the speedometer on the dash is off by about 1-2mph at 60mph.

07-13-2011, 11:24 PM	#3
david.gartee1 Drives: 2007 Yaris HB Join Date: May 2011 Location: Columbia, TN Posts: 7	Sorry, the Android app and the HU are very close. My tires are 185/60r15 made by GoodRide. It looks as if the wheels are the factory steelies.

07-14-2011, 09:14 AM	#4
Lil Abner Drives: 2009 3dr LB Manual Join Date: Mar 2010 Location: Dublin, Ohio Posts: 412	Honestly, I think your Android and HU are correct, the car is a bit off. But yours is just like mine. The tires are within the factory spec, so you're good there. The needle isn't adjustable, so you're basically stuck. But the majority of cars have the speedo off by a little bit. I'd say just get use to it. Like I said, for me, I can set my cruise at "60", but I'm actually doing 57-58.

07-15-2011, 02:32 AM	#6
david.gartee1 Drives: 2007 Yaris HB Join Date: May 2011 Location: Columbia, TN Posts: 7	Wow, mine is the same way. That just does not seem right. Over the life of the car, that could mean the real mileage is off by thousands. Not to mention the true MPG. I like to know that I can look at my speedo and know my real speed. Seems to me like Toyota should do something about this. I was cruising down the interstate at "80" tonight, and my GPS said 74.5-ish. To me, that is a problem.