how is the avg mph formulated?

It is total distance traveled divided by total time. The time includes when you are stopped by the car is in ready.

So you drove 260 miles in 10 hours (thus the 26 hrs). Now you've gone 73 more miles in 1.12 hrs. So this is 334 miles / 11.12 hrs = 30 mph. But you didn't really go 65 mph the whole time, so it really took a few minutes longer than 1.12 hrs...so you will see the math come out to something less than 30, then some rounding or truncation in the displayed value.


3PriusMike

 

post deleted

 

Wouldn't that be MPG? The OP was asking about MPH.

 

Yes it would, I removed my post as you were asking. :redface: I think Mike's answer is good .

 

I don't get it either. Mine has been at 18 MPH for the last 3 weeks. Nothing I do seems to have an effect on it.

 

I think there is a glitch in the MPH computation. Recently I had 100 miles of city driving at ~20 mph. Then I drove 200 miles of mostly Hwy at 70-75 MPH. The average MPH went up to only to 27 MPH.

 

Maybe a good check of the avg MPH would be to set it when you get up to speed on the freeway and check it before you slow to get off. Then your average should be the speed you are driving.

Another consideration, the more miles it has been since you reset Trip A or B the more miles it will take to notice avg. MPH or Cons changes.

 

Again, the math is total miles divided by total time.

100m / x = 20 mph (therefore x = 5 hours in your first segments)

Now you say you went 200 miles mostly driving 70-75 mph. But how long did it take? Did you sit at a few stop lights, etc? If you actually drove exactly 70 mph for the entire time, with no stopping, no acceleration, etc then you went 200 miles in 2.86 hrs. The math says it took longer.

So your totals would be 300 miles in 7.86 hrs...or 38 mph. But most likely you aren't remembering the exact data correctly. If you reset your trip odometer and do a few measurements and keep accurate track of miles (easy) and time (you have to measure) you'll see that it is very accurate.

The only method that makes any sense is for each trip (A and B) calculator that the Prius keeps track of miles, which it already displays and to keep track of "time." This is continually incremented whenever the car is in ready. The MPH display just shows the rounded/truncated division of these two values.

3PriusMike

 

Try driving faster. . . perhaps for a half hour or more

 

FWIW, I've validated the speedometer in this car against a GPS and by driving a measured course. I have to presume that the average MPH is pretty close to dead on. There's just not that many ways to screw up the math on this measurement.
The running MPG is another problem altogether...and there's a lot of documentation out there, and my own limited observations that suggest something close to a +2 MPG bias---but I'll defer to the "experts" on that.
Try resetting the A(or B ) trip odometer just as you're getting to cruise speed.

GOOD LUCK!

 

I have questioned the MPH on my car too, but when I have reset Trip B to different segments of my commute and Trip A to the total tankful, I have done the math on the different segments and it has come out pretty darn close.

 

Total time is calculated from the time the car is put into Ready to the time it is turned off.

 

The avg mph (or km/h) is total distance / total time to travel it.
My experience over 14 months of ownership says that the average is accurate and it works.
The mpg - L/100km is off (optimistically) by 6.5% average over 33 fuelings and 19.000km driven.
The speed display is 10 to 15% off (with 17" summer and 16" winter tires respectively) - this based on GPS Navi (Tomtom) measurements. (I need to drive 144km/h to drive at 130km/h...).
My father's Honda's Insight is *much* more accurate.
Any other user's experience on this?

 

My Cons reading (MPG) is optimistic by 5%.

My speed is fast by 4% to 5%.

My odometer is closer, it only reads 1% to 2% high.

I have 17" all season tires which were fairly new when I did the tests. Speed checked by my portable Garmin GPS. Odometer checked against mile posts along side the highway over 5 and 10 mile distances. Consumption was checked against odometer distance divided by gas pump quantity over a 3500 mile distance.

 

Take a trip. Pull off the Interstate, tank up, press reset, and re-enter. The MPH average will be just about right. But isn't that really a useless bit of information? I personally never look at that readout.