Big-Foot — I don't think that these same specifications apply to the odometer — just the speedometer. I'd expect that the odometer is calibrated to vary equally +/- about the correct reading. But, I haven't seen anything on this in the Repair Manual. The 1-sided speedometer calibration is due to legislation.
I have not yet been on the freeway with the Garmin in in the car. BTW - it was registering 7 satellites most of the time.
So - it would appear that our fuel economy figures would be inflated as well.
When I buy my new 17 or 18 inch wheels for summer, I will run a slightly larger (diameter) tire to help make up for the error.
Other people found the same thing with speed. However, when they used the GPS to calibrate the odometer they found that it actually read slightly low, so actual mpg was slightly higher than what's calculated using the odo or trip odo.
I took my car in to the Toyota dealer to have the 10% disparity looked at. As I said, I know that there is always a difference between speedometer reading and actual speed. ** But 10% is too much. **
Unfortunately, the master tech at the dealer used some tool called a dynamometer to check the speed, and he found that the difference was "within specification".
My own measurements using both GPS and several speed limit radar signs around town, consistently showed 10% or greater difference from the speedometer, but this "dynamometer" thing disagreed, showing a difference of only 6%-7% (still too much in my opinion but acceptable according to spec).
I am not yet convinced. When many measurements agree and one measurement disagrees, I tend to believe the many and doubt the one.
I am going to take more measurements with my GPS and radar signs this weekend, and then I am going to go and meet with the master tech at the Toyota dealership and talk to him face to face about it. Probably Tuesday. I am going to stay with this until I am satisifed with the resolution.
Unfortunately, the master tech at the dealer used some tool called a dynamometer to check the speed, and he found that the difference was "within specification".
I believe the master tech is right.
If you don't like the specification, you should try to change the ECE regulation No.39 .
I believe the master tech is right.
If you don't like the specification, you should try to change the ECE regulation No.39 .
Ken@Japan
I'm not arguing with the spec. I'm arguing with the measurements. I'm saying that I get at least 10% off no matter how I measure it. That is NOT within spec. The tech got less than 10% and that's the problem.
What's a dynomometer? How does it work? How do I know it's accurate?
These are my questions. I have measured with several radar guns, plus GPS, and they all agree. The dealer's scan tool disagreed. I want to resolve this.
OK. I looked at the ECE spec that Ken pointed to (thanks Ken). My speedometer is within that spec, even though it is more inaccurate than what the dealer says.
That ECE spec looked very European though. Is it what Toyota uses for American cars also? If yes, then I think I am done with this issue, dissatisfying though it may be.
Re: Speedometer 4-5 mph under actual speed
