This is all very fascinating. As a curiousity, what happens if different
size wheels are installed? Is there an adjustment to the settings possible?
As an example, the Accord coupe with 6 speed comes with 17 inch wheels
standard. The automatic has 16 inch wheels.

"Randolph" <trash@junkmail.com> wrote in message
news:3F255E1B.6C13F907@junkmail.com...
> Most car-based navigation systems use gyroscopes and speed sensors in
> addition the the GPS. ETAK (now Tele Atlas) built a working navigation
> system back in the mid 80's without GPS. It used wheel sensors only
> (gyroscope optional) and used the wheel sensors to calculate both speed
> and direction of turn (direction found by different speed on left and
> right wheel). It worked very well and even adjusted itself for tire wear
> etc.
>
> Even systems with GPS rely heavily on the speed sensor and gyroscope
> since this data is available much sooner (the gyroscope will tell you
> that you are turning WHILE you are turning. The GPS can only tell you
> that you have turned after you have driven in the new direction long
> enough to establish two nes GPS locations). The system will use GPS to
> calibrate the speed sensor, so the speed sensor data is very accurate.
>
> As a technicality, one could argue that the speed sensor really is a
> distance sensor. It gives a number of pulses pr mile regardless of how
> fast you are going. Unless you have some sort of time reference, the
> "speed" sensors will only give you mileage.
>
> Dick wrote:
> >
> > I'm just quoting from the Honda manual, page 3. "In addition, a
> > gyroscopic sensor and a speed sensor in your car keep track of the
> > direction and speed of travel at all times."
> >
> > Dick
> >
> > On Mon, 28 Jul 2003 08:14:06 -0500, TL <tlehman@visi.com> wrote:
> >
> > >I agree. The signal would have been lost. I'm curious, though about
> > >the sensors you mention. My handheld simply extrapolates when it
> > >experiences signal loss, ie, continues in the same direction at the
> > >same speed. After some predetermined time, it goes into a holding
> > >pattern and reports the lost signal. Obviously an auto-based system
> > >*could* have a speed sensor, but I'm surprised if it does. Calculating
> > >speed from the GPS readings should be much more accurate than the
> > >speed sensor in the car and it provides a vector speed (direction and
> > >ground speed).
> > >
> > >I'm not saying you're wrong. I'm just curious about the source of your
> > >information about the navigation system having a gyroscope and speed
> > >sensor. I've never heard that before.
> > >
> > >Tom