View Full Version : Speedometer off?

12-18-2011, 10:38 PM

I just put 383 miles on a tank of gas which took 10.22 gallons to fill. That equates to about 37.5 mpg calculated. The gauge reports 33.8. In my neighborhood and other places we have those speed signs that tell you how fast you are going vs. posted limit. My SE's speedo reads 2-3 mph faster than the signs are reporting. Has anyone else noticed speed descprentcies like this? Yes, I have the stock 16's with OEM rubber.

12-18-2011, 11:02 PM
My speedo was off with the stock 185/60/15's. With 205/50/16's, my speedo is dead on.

12-19-2011, 12:13 AM
the sign speed readout is not real time like your actual speedo. first it only captures your speed when you are in the beam of the radar and second there is always a delay between the speed and when it displays, so in other words in the time it takes the sign to process the data, your position has changed and your speedo updates a lot quicker than the electronic sign. your speedo is fine and the sign speed meter is just there to make you slow down and make you aware if you are going over the limit, it is not to be taken as a benchmark just an indicator

12-19-2011, 11:02 AM
Here in the U.K. there's a 10% allowance for speedo accuracy. Usually they read a bit high anyway, which I prefer as that reduces the chances of being over the limit!
Yours is possibly indicating that bit more anyway.

12-19-2011, 11:29 AM
I have nearly 4100 miles on mine now, and I can tell you the speedometer/odometer is accurate, but the problem is with the Average Fuel economy calculation. On level ground and going uphill it is accurate, but going downhill is a completely different story. The AVG Eco going downhill can not exceed a mileage of 99.9, when in fact the vehicle may be getting anywhere from 120 to 160 mpg during those downhill cycles. Therefore, the entire average computed is skewed downward anywhere from 1 to 5 mpg depending how much hilly terrain you are driving over.
This is evidenced at fill up time if you keep your odometer figures from last fill up. Calculating yourself is the only way in these vehicles with average economy calculators to verify your true mileage. On my 2000 Caddy Eldorado it also has one of these calculators, but it can't exceed 70 MPG going downhill and exhibits the same problem as the Yaris's calculator.

12-19-2011, 12:24 PM
get a scangauge and an GPS unit and program the scangauge to display actual
speed (use the GPS for 30 minutes above 75MPH to get actual reliable moving speed) no matter what the car speed pickup says.

you can dial a percentage offset and get scangauge to read dead-accurate
miles and speed regardless of tire size