I remember reading a thread somewhere about the hidden nav screen displaying the speedo. So i went out and took some pics. Turns out that the speedo is 4MPH faster than actualy speed.

I remember reading a thread somewhere about the hidden nav screen displaying the speedo. So i went out and took some pics. Turns out that the speedo is 4MPH faster than actualy speed.
Yup i've done it before, i was trying to figure out if the car looked more like a 1st gen or a delorean.

i have no navigation :(

The speedo is always set to read a little higher than actual road speed, at least that is a mandatory design regulation in Australia.

The reason behind this is to allow for various calibration variations in fixed speed cameras in different states of Australia.

For example, some speed cameras in Australia which are located in a 60kph zone but are only set to trip if you hit 66kph whereas some are set at 63kph and so forth.

You will notice the variation between speedo readout and actual speed will also fluctuate depending on the speed you are travelling as well.

The speedo calibration will also get knocked out of whack if you change the rolling diameter of your wheel and tyre combo.

Hmmm, just like the HP rating :D

It depends on how many sattelites the Nav has acquired. And also the geometry of the received satellite. Based in the location of the antenna, you are not going to get a good geometry at all. I would not be to quick too accept that number on the nav as accurate.

that screen does not use the GPS signal to determine speed, it uses an internal gyro..

Actually w/my experience as well as others (driving up upto police radar signs) my speedometer is only 2 mph faster then what Im actually driving not off by 4. There are two or three very old posts aboutthis issue and the consensus was that its 2mph faster. Here http://www.rx8club.com/showthread.php?t=26775 Being off 4mph would just be totally unacceptable. Im noteven too happy that its 2mph off anyway but Ilive w/it.

that screen does not use the GPS signal to determine speed, it uses an internal gyro..

You may be right. And if that is the case, the size of the wheel will affect the accuracy. It is not a gyro but rather a wheel counter.

You may be right. And if that is the case, the size of the wheel will affect the accuracy. It is not a gyro but rather a wheel counter.

Agreed- I've found 2 hidden screens in the NAV that display speed, but they're both getting their readings from the wheel speed sensors (same ones the speedo uses), which tells me that Mazda is artificially inflating the speed sent to the digital speedo.

every cars speedo is calibrated to show slightly faster then your going - saves the customers from accidental speeding tickets and manufacturers from lawsuits.

mine reads 1.6mph fast, tested with garmin V waas enabled gps reciver. not bad as far as i am concened.

beers

Yup i've done it before, i was trying to figure out if the car looked more like a 1st gen or a delorean.
I think it looks like a Venturi.

that screen does not use the GPS signal to determine speed, it uses an internal gyro..

Gyro's don't measure velocity, they measure angular displacement about an axis of rotation.

Accelerometers can measure acceleration, which given an initial velocity and some integration can yield velocity.

I think it looks like a Venturi.

looks like the messed up a 300z.

beers

the speedo's have to read faster to be legal in any country that i know of. Ferrari's, BMW's, and i image others such as Lambo's, read far in excess of 10mph higher than true. being within 2 mph is exceptionally accurate.