Prius Speedometer

[Julian30]

Hi,

Having recently realised that my Prius shows a speed of around 5-10% faster than I'm 'really' doing (and I understand why having read a few articles) my question is this:

When people post comments/tips/articles about 'best speeds for mpg', 'hypermiling' and anything else that has a speed element to it are they using the speed shown on the speedo or are they talking 'real' speed?

The reason I ask is because if someone has a scanmaster setup and gps (as some people seem to) and they say 68mph is an 'optimal' speed for long distance then do they mean 68 according to the Prius (which in my car is a real 63) or 74 according to the Prius for a real 68?

Hope that makes sense!

[Grumpy Cabbie]

It's UN mandate that requires the speedo to be about 10% under which the EU follows but the US doesn't and their cars are about 3 mph out. So beware when reading their quoted speeds compared to the reading on UK cars. Also, US gallons are smaller so 41 mpg US is 50 mpg UK.

http://en.wikipedia.org/wiki/Speedometer#International_agreements

[Julian30]

Cheers Grumpy

[MEP's Yaris GS]

Also worth noting, that unless wheels are not OEM, the car records the correct speed and distance traveled for ODO measurement, the increase on the displayed speed is software induced. You'll notice this difference if using live scan on a diagnostics tool.

[johalareewi]

When people post comments/tips/articles about 'best speeds for mpg', 'hypermiling' and anything else that has a speed element to it are they using the speed shown on the speedo or are they talking 'real' speed?

Depends what they used. Speedo, GPS, diagnostic tool.

As has been said, the speedo on the the prius is software enhanced to read higher than the actual speed. The speed available from the diagnostic port is not enhanced. Neither is the average speed reading on the trip meters, ;)

[Bibsy]

If you chuck your Prius into diagnostic mode and drive with it on then the screen displays the true speed (if you get to the right screen), which is indeed lower than the speedo reads.

That "diagnostic" speed will pretty well match that shown by my TomTom, which is why I'm happy to cruise through a 50mph set of roadworks with cameras at an indicated 55mph on the speedo.

[Grumpy Cabbie]

The Prius does indeed measure the correct speed but chooses to display the weighted speed.

My taxi meter used to have an option to display actual speed ( :) ) when it wasn't being used to measure fares. It would gain this information from the the speed sensor/sender unit on the car. Was always handy to have when driving thru 30 zones or 50 mph average speed check areas. The SatNav speed display whilst mostly accurate could be affected by hills etc so couldn't be relied on 100%, whilst the taxi meter could.

[Julian30]

Thanks everyone, very interesting indeed.

[Grumpy Cabbie]

Thanks everyone, very interesting indeed.

Oh we haven't finished yet. This subject has a lot more flogging left in it. We're all going to have to give our input, twice at least.

:)

[Bibsy]

Yeah, I was going to enter into the gps indicated speed and hills debate, but thought it's been done to death.

This one could run and run.

[Julian30]

Thanks everyone, very interesting indeed.

Oh we haven't finished yet. This subject has a lot more flogging left in it. We're all going to have to give our input, twice at least.

:)

Oh Lord, what have I done?

Yeah, I was going to enter into the gps indicated speed and hills debate, but thought it's been done to death. This one could run and run.

Ha ha, I know about hills so you can't get me on that!