My Speedometer is Lying; Is Your's?

nope. get it replaced under warranty. do you have oem tyre size? i suppose even then, there will be some change as wear reduces the diameter slightly. over pressurizing might compensate for this.

 

Speedometers over-reporting speed seems to be universal in at least Toyota cars, and apparently in other manufacturers also. Some say that it is an attempt to make sure that they don't get into trouble with regulatory agencies for under-reporting speed ("but officer, my speedometer said that I was under the speed limit"). There is a question as to whether the deliberate error is only in the speedometer, but not the odometer. People who have looked at the OBD-II data say that the internal readings are right; it is only the speed display that is skewed.

 

I have 17 rims on my Plug-in with 205-55/17s. These tires are taller than the standard 195-65/15s, and because of the taller size my speedometer is more accurate to actual speed - I'm now likely reading 1 mph over my actual speed rather than 2+ mph over actual speed.

 

ah, that supports my high tyre pressure theory, though it will be tough to pump them up to 17".

 

Speedometer - Wikipedia, the free encyclopedia

 

Interesting. I found that when I owned the PiP, it was adding .5 miles for every 15 miles I drove.

 

I am thinking my Gen2 was accurate, but I did notice Scan gauge gave a different number.

 

I live in Europe and I have noticed that ALL Toyota speedos add a huge 8% to the actual speed as given by a GPS. I often travel to the US and rent cars whenever I go, opting for a Prius if available, and there ALL Toyota speedos (not only Prius but all models) are dead on spot (give or take 1%, never noticed any more than that). I raised the problem with Toyota France; They refuse to do anything and tell me it's a normal situation, it's intended that way. Well, I strongly disagree: given the present state of technology, a consistent 1% error is all what we should be expected to put up with, given the fact that tire pressure and wear will account at the most for a 1% inaccuracy. Having to put up with a speed exaggeration as enormous as 8% is totally ludicrous, and I don't mind letting everybody know that I find this situation, and even more Toyota Europe's attitude towards the problem very annoying, to say the least.

 

Import a US Model Prius to France, and then you will not be annoyed!

 

Yeah, well, I wish it were possible. Unfortunately doing that would cost me an arm and a leg adapting it to European standards... Who said the world has become a free trade zone? They probably missed the small print !

 

Maybe the Japanese have something against the French, too much cheese!

 

For sure there are a lot of cheesy cars in France, that's why I would never buy one !

 

I don't know about odometry, but my speedo is always 1 mph higher than all of the various digital speed detection devices I encounter on my daily journey.

 

My experience is that all cars in EU are over-reporting speed, it's not only Toyotas. Passat may lie only 5% and Toyota 8%, big deal, I adjust my speed 10 kmh over 50 kmh sped limit and I'm on the safe side.

 

My speedo reports 2 MPH faster than actual at most speeds. I have not checked the odometer yet.

 

There's a traffic regulation in Europe that all speedos must show exact or higher than actual speed. Toyota choose to add a fair amount of surplus kmh to stay on the "safe" side of the regulation.

I feel stupid and humiliated for my authorities' message to me: "You're not capable of evaluating speed yourself, so your car will do it for you!"
Machine has to provide as accurate data as possible to human. It's human's job to judge what is too fast. Why did they give me a driver's licence then?

 

Putting the various federal and/or international regulations aside for the moment, no manufacturer would be willing to under-report actual speed on their speedometers due to the massive amount of litigation that would ensue from owners ("I was ticketed for doing XX mph in a YY zone. My speedometer showed that I was doing YY the whole time.")
Manufacturer's are going to err on the side of caution since their bottom line is at stake.
Once you accept that the speedometer in any car is going to read a little high, it becomes one less thing to agonize over.

 

I've only check it against the roadside radar displays. Almost always my speedo is showing 2mph higher, occasionally 3.

 

I compared mine against GPS and mile markers over a 100 mile run, and they pretty much all agree.

My beloved company finally put a GPS unit in my car so I have a pretty powerful incentive to make sure that my speedo is fairly accurate.
I'll repeat this the next time they re-tire my car, but unlike the fuel efficiency guesstimate, the speedo seems to be accurate.