Cruise Control Adjustment

Valid suggestion, although I don't think it's quite that bad. I had a Mitsubishi once that consistently read 5mph higher than its actual speed, but I've never caught a Prius reading more than 1 or 2 mph high, and never low, as you point out. I think there's some kind of law that makes this kind of miscalibration necessary.

Richard

 

You are correct sir. It seems to be a technology that they like to bundle with the adaptive cruise control and Adv. Tsch. Pkg. just not as new as I had thought. Thanks for the info.

 

My previous cars, Mercedes, were always right on. Maybe 1-2% offset.
So it can't be a law.
My Ducati mc is also pretty optimistic....like the Prius, but it's an italian macho bike, so you can expect it.

If it's not a law (it isn't), why display a higher speed while the OBD info is correct?

 

"If it's not a law (it isn't), why display a higher speed while the OBD info is correct?"

It's not a law, it's a regulation. From Wikipedia on speedometers:
European Union member states must also grant type approval to vehicles meeting similar EU standards. The ones covering speedometers [4] [5][6] are similar to the UNECE regulation in that they specify that:

• The indicated speed must never be less than the actual speed, i.e. it should not be possible to inadvertently speed because of an incorrect speedometer reading.
• The indicated speed must not be more than 110 percent of the true speed plus 4 km/h at specified test speeds. For example, at 80 km/h, the indicated speed must be no more than 92 km/h.

When you have a digital readout there's typically at least a one-digit uncertainty in the least significant digit. So, if the regulation says it must NEVER read low, it would make sense to add at least one mph to the reading so that in the worst case, it would read that actual mph. Which means that the uncertainty of the LSD plus the safety factor of adding 1 means that occasionally it will read 2mph high. Additional errors in the actual measurement might encourage the manufacturers to add an additional safety factor of, say, .5, which means that occasionally it will read 2.5mph high.

I'm all for accuracy and precision, and would certainly prefer that my speedometer read correctly. One solution would be to add an extra digit to the readout, e.g., 52.4mph, but that might add cost, and is really pretty meaningless except to fanatics such as those of us who care about this thread.

Richard

 

I would be very happy if it was only 2-3 mi/h off. Like the Mercedes.....

I have the feeling that Toyota is trying to .......me by making me believe I'm a very fuel efficient driver.....in the meantime truckdrivers are on my rear bumper :not very good for the Prius image.

Maybe I have to put bigger wheels in the car....

When I put 215/45/19 wheels on the car, my speed will be 129.74 km/h when the speedometer reads 120 km/h......which is about right to counter the Toyota ......(I guess I'm not allowed to write down my feelings)

 

So, since the speedometer is slightly overestimating your speed, you're going to swap out the tires for larger diameter? Are you serious?

 

I've owned 40+ cars over a lifetime (of at least a dozen makes) and all of them were the same. The speedometer read high ... except one and I got out of a ticket by having my speedometer recalibrated and the judge accepted that as a plea.

 

Yes....sounds crazy not?
The things you have to do for having to see the right speed.....

 

Nowadays speedometers are good enough to display the speed without being to much off.
The Prius "knows" at what speed you are going: check the OBD2 data.
But the guys at Toyota EU want me to think I'm going faster than I actually do.....
But I don't need a chaperone....I'm old enough to decide what speed I want to drive, based on the info I get from the car....but that info is wrong.