Here's Why Prius Drivers Drive Like That

Prius drivers are annoyingly slow because Toyota purposely sets the speedometer roughly 5 mph higher than actual speed. So here's the poor Prius driver thinking he's drivingt the speed limit when he's really driving 5 mph under the speed limit, getting a bad attitude from other drivers for driving so slow.

Noticed and documented this via several radar speed limit signs and when I went from the 195 tires to 205 snow tires and the Prius speedometer matched the police radar speed.

 

Nothing unusual with that. My RAV4, my Goldwing, my Wife's vehicles all showed lower mph than the GPS, actual readings. Nothing sinister, lots of reasons for that. Calibration is just one.

 

Good read.

 

Two "sinister" issues with Toyota purposely showing phony higher than actual speed.

1. It causes Prius drivers to drive slower than they intend.

2. It causes Prius to show higher than actual mpg.

Both are dishonest.

 

It is a requirement to never show a slower than actual speed in Europe, and in the US it is a lax tolerance. So ALL vehicles sold in the US err on the side of caution and show lower speeds.

The European regulation, ECE-R 39, is more concise, stating essentially that the speed indicated must never be lower than the true speed or higher by more than one-tenth of true speed plus four kilometers per hour (79.5 mph at a true 70). Never low.
In the U.S., manufacturers voluntarily follow the standard set by the Society of Automotive Engineers, J1226: Manufacturers are afforded the latitude to aim for within plus-or-minus two percent of absolute accuracy or to introduce bias to read high on a sliding scale of from minus-one to plus-three percent at low speeds to zero to plus-four percent above 55 mph. And those percentages are not of actual speed but rather a percentage of the total speed range indicated on the dial. So the four-percent allowable range on an 85-mph speedometer is 3.4 mph, and the acceptable range on a 150-mph speedometer is 6.0 mph.

 

funny replies. i especially love the jealous volt and vdub owners.

 

Excellent article and very well written. Thanks for sharing. This guy describes my feelings and attitudes of driving a Prius. It's fun to play the mileage game when gasoline approaches or exceeds four bucks a gallon.

 

Actually, the speedometer is only 1mph-1.5mph off with the 195/65/15 tires equipped. I've measured this in two different GenIIIs with 6 different sets of tires. The most anyone else on the forum has measured was a 2mph error. With 215/45/17s the error is 1.5mph-2mph. With 205/50/17s the error is 0mph-0.5mph.

 

Fun. I had a Honda Odyssey that was off by 8 mph at 65, and, yeah, found with a GPS, not to mention the mile markers and a good watch. Complained about it to the dealer. They claimed that anything less than 10 mph wouldn't require a warrantee repair.

However, the 2010 Prius III currently owned shows 66 when the GPS speed is 65. A previous discussion on Prius Chat had a number of people saying that this is what they were getting.

If you're off by that far - go bug the dealer. May be something wrong.

As a mentioned in a chat quite a while ago, a few of the Big 3/4 in Detroit in the 60's had things skewed so the average car was reading 5% low. This was complained to the FTC, which investigated. Detroit said they were making things "safer". The FTC said a mile is a mile and things got fixed. (Source: Originally from my Dad, but documented as well in Unsafe at Any Speed by Nader).

KBeck

 

i have a GPS radar detector Escort 9500ix and the speed is dead on, unlike my BMW and Audi that's about 2-3 mph slower.

 

I see my share of Prius's around where I live, and I don't notice them driving any slower than anyone else. I think perception is not reality. I typically drive at least 5 mph over the limit, but get the feeling drivers behind me ASSUME I'm poking along and holding them up. If I'm in the left lane, I'll pull over, only to see them zoom past me doing 70 in a 55, only to realize a short time later they're going too fast and slow down! LOL - stupid idiots!

 

Many comments here about the MPG calc being off 5% which would dovetail with the speed being off by 5%.

The police radar signs seem a good guide. They were consistently showing about 5 mph less than the Prius speedo. Once I swiched to the 205 tires, the were within 1 mph.

 

Not my cars.

The Prius mpg is off by 6% (3 mpg @ 52 mpg ind). My speedo is only off by a constant 1.4 mph (measured by gps) at all speeds.

My Acura's is off by 1.5 mph and the Jeep by a little less than 2 mph.

Is more like a constant bias built into the speedometer.

Yet, in all of my cars the odometer is dead on with the gps distance travelled.

 

My hand-calculated MPG is always about 5% less then the on-board computer says, and the speedo is off about 5% at highway speeds.

 

I diagree regarding the speedometer showing slower than actual. Well, I agree, but all cars on the road do this: there's regulations requiring speedometers to read on the high side. I'm vague on details, but in a nutshell: your speedometer can read anywhere between high and spot-on, never low. So manufacturers tend err in the middle of that spread. Not a bad idea.

Regarding the mpg readings in the dash, yes, this is BS from Toyota. I think they're counting on free advertising from drivers who don't calculate their mileage, just rely on the inflated readings. To be fair I've heard the Prius c and v (and maybe late model regular Prius) are closer to reality. FWIW, in over 2 years vs dash display, the average error in my case is just over 8%.

In comparison: our previous Honda Civic Hybrid dash display consistantly displayed mpg slightly lower than actual. Or occasionally spot-on. This was in liters/100 km. If it said 5.0, calculated would typically be 4.9.

 

Actually all car manufacturers does this to their speedometers. I tested all 5 of our cars with GPS they are all show high MPH than real life.

 

This guy's article pretty much matches our situation completely. My wife drives the Prius normally like a normal car with no conservation of the gadgets working together to achieve maximum efficiency. So she gets 35 mpg, me on the other hand watched too many youtube videos on how to achieve maximum efficiency with the Prius. So I get about 45-50 mpg.

My wife did mention that she really enjoys the way I drive the Prius (smooth and slow), she said she feels safer and more relaxed than riding in my other cars (which I always haul nice person in and scares the shit out of her all the time).

I did see something in the article that I would like to stress. He said "(And fellow Prius owners, please stay out of the left lane on the open road, OK?)"

LOL!

 

That would make sense. US mfg's can be off by 5% and for Prius being off on high side would also boost mpg, the main reason people by the car.

I like being acurate so I'll stick with the 205 tires when I switch out the snow tires.

 

Just be sure to perform the calculations. With a 205/50/17 tire my speedo was dead on BUT the odometer read slower. With a calculation included for the odometer offset my mpg was still 5%-6% too high.