Speedometer incorrect and Cruise Control Wrong

This is well known, hardly unique to the Prius, and opinions vary about why. Some good reading on the subject: Vehicle Speedometer Accuracy | How Fast Are We Really Going | OEC

 

i just go 2 over.

 

I have noticed and have taken that into consideration when using the cruise control. No biggie!

 

Here in the UK we have a 10% over read.

 

Speedometer readings are optimistic since no manufacturer wants the liability of it reading lower than actual speed.
Speedometer - Wikipedia

 

First world problems....

Seriously you could just drive the speed the speedo says, not a crime to go 1~2 mph slower than exact limit lol.

 

The Speedo is much better than my last car, a 2010 Ford Fiesta, which read 108km/hr at an actual 100.

The PRIUS is about 2km slow at almost all speeds - you can verify it with a SatNav/GPS which is much more accurate.

 

Mine is the same. I just live with it...

 

Blad123's link suggests that the manufacturers would pick a single offset for the world's markets, so a single setting works in both the US and the UK.

But the bulk of past comments are similar to Kithmo's experience: Euro market overreads appear to be fairly consistently higher than North American market overreads. And not just on the Prius line, but on automobiles in general.

 

If the speedometer was absolutely correct at time of purchase once you put 20,000 miles on your tires it will no longer be accurate

Posted via the PriusChat mobile app.

 

Not by as much as you think. And certainly not by enough to acocunt for the many observations posted to PriusChat.

Forget what you know about circles. The contact zone on the ground is flat, not round. When properly inflated and loaded to their normal working range, a steel belted radial tire's rolling circumference is set mostly by the length of the belts beneath the tread. Those belts do not shorten as the tire wears and ages. You can figure their length by looking up the 'RPM' spec for your tires -- Revolutions Per Mile.

This does not apply to old fashioned bias ply tires, bicycle tires, or tires carrying very light loads.

 

Can't find any reference to it ATM but think UK mandated a lower speed indication on motor vehicle speedometers.

 

IIRC, UK, speedo cannot read under but may be up to 10% over. So when speedo reads 77 mph you're only doing 70 mph.

 

My Tundra reads 58 @ 55, Honda Odyssey same, kid's Ford Escort 30 @ 25. As was said, no car maker wants to be found producer vehicles that travel faster than indicated - too many lawyers in the world.

 

Almost 30 years ago I once had a Florida State Trooper verify that my hacked 240 SX was in fact traveling at 120 mph when my speedo was only indicating 115. Of course there were no numbers on the dial past 115 so ...

That was also the day that I learned to never trust reviews presented in enthusiast magazines. Either R&T or C&D had done one on the new 5.0 liter Mustangs that the Florida State Police were getting, and between the old style light bar on the roof, the extra weight and auxiliary gear drag on the engine, they reported that the cars had a top speed of only 105 mph.

This was all figured somewhere in the back of my mind when my wife and I decided to take an unscheduled quickie vacation and drive down to the Keys for the week. Armed with my new Escort radar detector it never occurred to me to bother watching my rear view mirror as I took advantage of my wife's napping in the front seat and decided to check out warp speed. Imagine my surprise when the Florida State Trooper, driving one of those very same 5 liter Mustangs, hit his lights and siren as he pulled even with and then passed me on 7 Mile Bridge?

Later, as he waited to get my autograph, I casually mentioned my surprise that such an non-aerodynamic vehicle such as he was driving, was able to travel so fast. He let out a little giggle as he handed me a $280 souvenir and said "you don't really think we'd tell those magazine reporters how fast we can really go do ya?".
I had never even mentioned the article, but apparently I wasn't the first reader that the Trooper had met.

 

That's my experience in almost every vehicle I've ever owned......cars, trucks and motorcycles.
But HE is saying his is off in the other direction.
I would think that is much less common.

Different tires can cause the speedo to be off.

 

As with all the reports, the one I linked to is speculation. Unless and until the automobile manufacturers choose to tell us what the reason is, we'll never really know.

 

Okay - How about...
Speedometer readings are typically optimistic since no manufacturer wants the liability of it reading lower than actual speed.