We're really talking geodesy rather than electronics.  The good ole DoD used to feed error codes into GPS signals but some years ago realised that was pretty much a waste of time so stopped.  So these days the satellite (or rather a bunch of them) will tell you exactly where you are. Unfortunately, you very rarely want to know exactly "where" you are.  You really want to know how far it its the next town - or the next corner.. WRT speed, even if the location was out by 100 feet it wouldn't matter.  The GPS unit measures the distance from where you are now to where you are in a few seconds very accurately (depending on the number of satellites it can see - and that's gererally "enough"). It knows the time difference very accurately and so calculates speeds very accurately.  Once you work out your speedo error (my modern VW reports about 9km/h fast) the speedo and GPS will agree exactly.  My GPS updates speeds several times a second (must check if the manual actually gives a refresh rate).

The second point does need consideration. Its a bit of a waste of time to try to use GPS to navigate through NYC for example....  Although it can be a learning experince.  Some (all?) GPS units have a dead reckoning feature.  So if you're driving along at 30 mph and lose signal, the machine will continue to update you position based on your known trajectory.  Its somewhat amusing to hit a red light, stop and watch the "you are here" cursor march off into the distance.  When the next satellite pops into view the system resets to reallity.

Your error in the Amazon was caused by the different mathematical models (the geoid) the South American map maker and your GPS designer used to depict the earth's surface.  Our local (rural) fire brigade has spent a reasonable amount of effort "ground truthing" our local maps.  We have a freeway running through our area that has very limited crossing points so we have plotted its "GPS" position in red on our maps so that if we need to go a particular satellite reference close to the freeway we can tell immediately if we should be on the north or south side of it.

The basic physics of GPS hasn't changed.  What has improved is the number of satellites (more satellites = faster response time) and more maps based on the satellite geoid (so when the GPS reports you are at an intersection, you can look around and check for crossing traffic.

Sorry, confessions of misspent youth as a geodetic surveyor....

Really the only downside to a GPS based speedo will be line of sight to the satellites..  But there are lots of other extremely accurate electronic distance (speed) measuring devices on the market. 

Cheers, Ian

Thanks for calling. Guess the other comments on the other forums were wrong. Guess not waiting for the next sale won't be a big deal.  Thanks again!

I called about that - they said that all that does is remove the requirement to buy multiple gauges.  In other words, you don't get 20% off on top of 15% off.  But if the sale is 20% or 25%, you'd get that instead of 15%.

Yeah I saw that and my total will be right around yours, but I was reading on some other forums that speedhut offers holiday sale on top of their kit deal.  I guess they had a Thanksgivings promotion for an additional 20% and a 4th of July at 25%.  That would sale me some nice money to spend elsewhere on Victoria (my minis name).

When you buy three or more gauges, it is 15% off each one.  I spent around $750 for all of them.  I got the 4" GPS speedometer with the built-in fuel gauge and indicators, 4" 0-6000RPM tach, and 2-1/16" each of the voltage, oil pressure and water temperature.

Thanks, I was hoping that they would.  So overall you would say you are happy with your purchase?  Only want to do this once since I will be spending this kind of money. Going the same route as you replacing all the gauges.

Hopefully they will have a holiday sale coming up soon.

It has a pot to adjust the brightness.

I don't remember the actual accuracy level of current GPS but whomever brought that up was correct.  Just FYI Garmin units use the same or similar interfaces between all their devices with minor changes from year to year.  Most will have that "dashboard" interface available.  EVEN MORE INTERESTING HOWEVER, is that you can get a connector to hook up to your car's on board computer.  Now, I don't know how well that would work with a mini sporting a honda motor, but its an interesting thought.

//www.youtube.com/watch?v=GgHV3v7ZYDM

Looks fairly responsive.  I like that they have orange background and lighting, too!

How is it at night?  Not too bright or anything?

I know little about Electronic devices, but someone told me that GPS is only acurate to within 100 feet, which would not provide very acurate Speedo readings if that is the case.  Also, how often does the speed update?  if you are accelerating or decelerating rapidly, I would want the speedo to be able to keep up.  Finally, I had a Garmin hand held GPS that I bought years ago for a trip to the Amazon.  once in the jungle, it didn't work at all, since the trees blocked the satelite signals.  I tested it at road locations in California, and the coordinates would plot out as much a 1/4 mile off the Topo maps I was using.  I know that GPS has gotten better in last 15 years, but before I bought a new one, I would like to make sure it can see around obstacles, like mountains and trees, and be acurate for speed within one or two percent. 

I went with the standard blue. I like it.

What color backlighting did you go with?  I was thinking of getting the white dial/black font with white glow for the background. 

They're not all GPS; they also make regular electronic speedometers.  They don't make any mechanical speedometers, however.

Thanks for the explanations.  I understood that the Speedhut speedometer was a GPS unit, so I was just confused by the statement (on their website) that says:

"Works with all speedometer sensors/ transmissions .5 - 200 volt signals."   If it is GPS and should only require a power connection, why would you need to bring

a signal in from your transmission or speedo sensor? 

The tachometer works from a connection to the '-' on the coil.  Since this is the same as the original tach, you could even use the original wire.  It comes programmed for an 8-cylinder engine by default, but reprogramming for a 4-cylinder is pretty easy. 

For the voltage gauge, any powered wire will do. 

For the oil pressure gauge, I just fitted their 1/8" NPT sensor into the tee that the previous owner had fitted for a capillary-type gauge.  The sensor comes with a molded connector on 6' of wire.

For the temperature sensor, I drilled out the head in the recessed area below the thermostat housing (that used to be tapped for a temperature sensor at one time in the Mini's history).  I tapped it 1/4" NPT and used a reducing bushing provided to fit the 1/8" NPT sensor.  The sensor comes with a molded connector on 6' of wire. 

For the fuel gauge (inside the GPS speedometer), it was already calibrated for 33 ohms full, 240 ohms empty which is close to the 30-240 that I found for the Mini. I just hooked up to the sender.

For the GPS speedometer, I mounted the antenna on the dash.  You can see it in my picture.  It is central and I only had to drill a small hole (around 1/8") for the wire.  I mounted it with double-sided 3M tape.

All of the lighting and power for the gauges have one common connection that includes a daisy-chained set of molded connectors that plug into each gauge.  Very easy.  It also has a rheostat for the backlighting level that I mounted under the dash.

My bezel for the speedo and tach is a 1/4" piece of aluminum that I had laser cut to the shape of the opening in the wood dash.  It was very slightly too big so I had to shave the wood in one area. The way I made it was that I put the dash on the photo-copier at work and had it email me the scan.  I imported it into AutoCAD and traced the opening and sent the file directly to the prototype shop.  It only cost around $30 (for two, to meet minimum pricing).

Since I also re-wired the entire car as part of this project (with a generic 12-fuse kit from Speedway) my wiring was accounted for in planning.  I also added an alarm and new stereo at the same time.

Speedhut Speedo is a Global Positioning System (GPS) unit...so from satellites.  Therefore it doesn't care what gearing, what wheel/tire sizes etc.  Obviously doesn't work in underground parking garages, tunnels, snowsheds etc. but those circumstances are an infinitesimal part of most driving. 

I am still looking for a speedometer solution similar to this - but one I can install the mechanicals of the Speedhut speedometer inside my Smiths unit to retain the original appearance, but with good, accurate movement inside.  I replaced my Smiths tachometer guts with a modern electronic Sunpro tach movement of the same sweep and RPM range, and this achieved what I wanted.  Where does the Speedhut speedometer get it's signal from?  It says:  "Works with all speedometer sensors/transmissions .5 - 200 volt signals."

That looks so nice!

Im having troubles deceiding if I want a setup like yours or keep it all center like the car has now....