Toyota why is the mpg readout not accurate?????

NHSTA under DOT: Regulations Section | Federal Motor Carrier Safety Administration

 

GAO? When they buy Govt vehicles? Or perhaps trial lawyers?

Bob Wilson

 

(1) That gov't regulation isn't for any SAE standard;
(2) That applies only to commercial vehicles, not passenger cars such as Prius;
(3) That tolerance works out to +/- 10% at a single speed of 50 mph. The Prius MPG display error in question is falling inside that range, so an equivalent requirement would not force Toyota to improve anything.

 

The government (DOT/NHTSA) does not mandate SAE standards, they mandate FEDERAL standards, which supercede SAE "best practice" industry-design standards.

And, yes, that is a commercial mandate, but most commercial vehicles use speedometer and odometer devices (they're almost ALL electronic, not mechanical, anymore) interchangeablely across their products...and SAE J1226 is the current example that USA electronic speedometers and odometers are designed to...even though there is no specific federal mandate (anymore) about speedometers and odometers.

 

Have you guys read Bob Wilson's posts on this matter ? The meters (and fuel economy) are affected by tyre circumference. Unless GPS is proposed as a mandatory device for accurate distance measurement, a basket of biases can be expected.

If my arithmetic is correct, 16" tyres will result in pretty accurate readings.

 

^ We're straying. "16" inch tyres" is meaningless without elaboration to define the outside diameter, ie 195/65R16. And "pretty accurate readings" of what?

Can we agree:

1. With either stock tire, 195/65R15 or 215/45R17, the odometer will be reasonably accurate?

2. The speedometer's positive bias is legislated, intentional, to encourage drivers to slow down. Further, that the speedometer inaccuracy need have no impact on other values the car displays, it's an end product.

3. The mpg display is reasonable consistent, say +/- 2%, but grossly skewed to the positive side.

4. If point #1 and #3 are true, there is no compelling reason why the mpg display could not be accurate within 2%.

 

I have not. But I will look into it.