Speedometer discrepancy

There are laws in various localities that impose penalties if the speedometer is encouraging speeding. Some actually specify how much off the speedometer should be.

Those other devices are not required to be off.

(the US is very lax about this)
49 CFR 393.82 - Speedometer. | US Law | LII / Legal Information Institute

Here is an Australian rule:

Speedometer Accuracy - Speedo Regulations - RACQ


And Europe:
Speedometer Scandal!

 

The speedometer reads high by design/legislation, and yeah it's in the (vain?) hopes that people will drive a little slower.

The displayed mpg (at least on my 3rd gen) definitely is exaggerated, to date difference is 7.5% vs calculated, at least for me. I would lay this one at the doorstep of Toyota's marketing department.

No, the odometer should be (and likely is) reasonably accurate. Gross inaccuracies especially if it was accumulating miles too fast, would interest prosecutors. Honda had such issues in the past IIRC.

 

i have, and drive a couple miles over.

 

My 195/65-15 tires make my speedometer and my garmin match, what size tires are you on.

 

Mine matches the roadside speed (radar controlled) display down the street from me.

 

I use GoogleMaps with GPS HUD Speedometer (AscendApps) which is flawless, really useful, and is well-supported! The Speedometer app is GPS driven and I've found it to be pretty useful. I was getting hammered driving for a local courier/messaging firm. They have GPS tracking on all their vehicles and get e-mails when anyone breaks the speed-limit, and on one memorable trip a month or so ago up to South Burlington, VT I received a frantic call from the dispatcher to go easy on the speed as he was getting swamped with e-mails stating I was going "80", "85", "90" mph on I-89N in Vermont. Well, it was a gorgeous day for a Sunday afternoon drive in the Green Mountain State, but I'd been told that this delivery was time-critical and so I admit I was rather pushing it a bit! (…well, who wouldn't?) I made it with 15 mins to spare, but eased back on the return trip, but was hauled in over the carpet by the boss-fellah, who was quite reasonable, but I swore that it would never happen again! …and now thanks to AscendApps, I now have the true speed shown over the map display, so there really is no excuse! I drive all manner of Toyotas (from Corollas, through Yarises, to all models of Prii) and have found by using the AscendApps Speedometer that in general their speedometers tend to be fairly accurate, and any error tends to be over-reading so 65 (say) on the GPS shows as 66 or 67 on the car's speedo!
I rest my case, M'Lud!

 

Wait! Are you saying the app allows someone to email or call you on your cell phone when you go over the speed limit? and you agreed to that term?

 

Nope! Re-read my e-mail. I've no idea (nor do I care) what software my firm uses, but the app from AscendApps allows me to constantly see (…and have a voice reminder if preferred) of my GPS speed.

 

Yeah, I got that point. I was just curious how the dispatch got hold of your cell phone number when you were speeding.

Edit: On second read, I realized I missed the part you are driving for a local courier/messaging firm. That explains why despatch new your number. Duh!

 

That regulation doesn’t apply to private passenger cars, for which there is no U.S. speedometer standard, as I’ve explained before, in these threads:

Speedometer incorrect and Cruise Control Wrong | Page 2 | PriusChat
I joined the club, stuck at 299,999 | PriusChat

 

Mine too. We have several of those radar speed signs in the city. "YOUR SPEED IS..."
And my Prius speedo matches the radar readout perfecrly.

 

Actually, it is because Manufacturer's don't want the liability if the speedo should read LESS than the actual speed, and you get a speeding ticket. It typically will read about 2-3 mph high.

 

Mine too. Always exactly the same as roadside the roadside radar speed display. JFI, the display is for 35 mph zone road where people tend to drive way over the limit, and my speed is anywhere between 28 to 38 mph.

 

US standards are for the manufacturers, State laws would be for an individual's car. True.

 

No, in this case, the state laws are preempted. As NHTSA wrote in the Final Rule:

In revoking this standard, NHTSA intends that other levels of government be preempted from establishing similar requirements. The agency believes that regulation of speedometers and odometers is not appropriate at this time at any level based on the absence of data indicating regulatory methodologies exist which would in fact yield significant safety benefits. Contrary regulatory decisions at other levels of government would negate the agency’s exercise of discretion and undermine the Congressional goal of uniform national standards.

Further, refraining from regulation will facilitate experimentation by the manufacturers in providing more effective ways of improving speedometer and odometer performance and thus possibly providing significant safety benefits
​

— Federal Motor Vehicle Safety Standards; Speedometers and Odometers; Controls and Displays, 47 Fed. Reg. 7250 (Feb. 18, 1982).

 

Comparing with my ScanGauge, no speed correction, tire psi of 40:
When Prime says 45 mph, ScanGauge says 43 mph.
Also, I've found the sonar "Your speed is" in the area to be at or slightly below my hybrid's reported speed.

 

In the U.S., this gets the attention of not prosecutors (it isn't a crime), but rather liability lawyers who love to file class action lawsuits over alleged product defects. I received such lawsuit notices on my past Honda and Subaru (neither of which displayed the alleged problem), both companies settled with 2% warranty extensions.

Now my newer Subaru's odometer reads about 1.8% low, while the speedometer still reads slightly high. But curiously, its displayed MPG is almost perfect, not skewed by that 'tuned' odometer.