speedo true speed

[Way2go]

Now, your results could be achieved by taking the readings as you go through the gears, but if that's the case then it's useless as referencing for calibration

Surely what gear you're in won't make any difference if the speedo is geared off the final drive? Maybe you're thinking of the rev-counter giving different values for different gears versus roadspeed?

[JayW]

Actually, that's a very good point, well spotted! In which case the results are definitely flawed!

[kiwi]

30kph speedo 28kph Dyno
50kph 50kph
80kph 82kph
100kph 105kph
120kph 125kph

There must be something wrong with somee of your equipment?

Despite speedos not being accurate, the results are always linear (if the error was 10% for example).

But, your readings look more like this:


Now, your results could be achieved by taking the readings as you go through the gears, but if that's the case then it's useless as referencing for calibration (even mentally) as there's no way you'll always be in the same gear at the same speed.

Nothing wrong with the equipment and this was before I had a GPS btw! They even double checked the readings because it was disputing a speeding fine.

Not long after was when the GPS dropped in value and I have checked it with three yes three differant makes on the dashboard at the same time tomtom, navman and Garmin. What I did note was a slight lag it readings change matter of split second nothing major unless of course you slamming oin the brakes with plod heading the other way. Anyways reading pretty much checked out the same with GPS. Weird speedo I have previously posted about this weird result.

[kiwi]

You might want to have a look at the wiki, the 'constellation' looks like this;



And that is the ideal model, and not the final pattern, which prefers land mass to perfect pattern.

They're obviously not in geosynchronous orbit around the equator!

As for marine use, if your 10ft out of position in deep sea, it doesn't matter, so you can live with one less satellite. I've done rather a lot of reading on the subject, specifically on the use of different algorithms to adjust for error in GPS tracking systems, and while I wish i knew more, i'd like to think I've got some of the basics covered.

After reading this I would dare you to debate that topic on a New Zealand forum to the ones who swear by the GPS as being the end of all arguements to your speed.

Talking of that GPS tracking in vehicles is actually becoming more common in NZ from commercial outlets and employers also the Transport Agency is using it to calculate Road User Charges on Heavy transport vehicles. Plus with that is you dont get charged for the off road kms clocked up eg Farms and in my line of work tourism shuttles. I also noted that dashboard Cameras are coming fitted with GPS systems now.

Also yes these GPS tracks have been used in court to challenge motoring convictions, surprised the traffic enforcemnet agencies has not picked up on the flaws yet.

[docchevron]

We have GPS on our buses in work, infact each of our buses have 2 different GPS units, and will have 3, for long winded and boring reasons, mainly being each piece of kit doing a different job from differing manufacturers and no unit "talking" to the other..
Anyway, whilst GPS isn't bad, it does have flaws. For example, sometimes some of our buses track as being in the north sea, when infact they in Bedminster, some vanish altogether and some "shadow" their location by as much as 4 miles.
The other fun bit of the drivegreen losing GPS lock on is errant recordings of our buses being capable of over 300MPH. If only that were true..
I've had a Garmin and my own ViaMichelin running side by side in the 16v and the speed was 2MPH different between them. Both read higher than the speedo by 5 and 7MPH respectively.
Which of the 3 is right? No idea, maybe none of them, I tend to drive to the speedo since I'm pretty damn sure that reads high.
Safer that way than a ticket.

[ghaddon1701]

Mine reads 68mph on the satnav at an indicated 70mph. Sometimes 67mph. Also my Garmin satnav when showing 30mph tallies exactly with those speed signs in 30 zones which tell you your exact speed. You get a nice green thank you message aswell .

[MULLEY]

I've always kept to the Satnav indicated speed of 50mph (car speedo is reading 55) on the motorway when they have those infernal average speed cameras, never received a fine, so i'm going with the Satnav for accuracy on this. Can't comment on Kiwi's anomalies, different continent, perhaps the altitude might be a causal factor? or the satnav is an inaccurate one (is it an oldish unit?).

[kiwi]

Can't comment on Kiwi's anomalies, different continent, perhaps the altitude might be a causal factor? or the satnav is an inaccurate one (is it an oldish unit?).

Easy cop out

You might actually have something with your oldish unit comment! Leaving the unit on the dashboard is probably not got for them especially when the unit is getting roasted in the sun. Over in Australia one thing thats come out of this years record temperatures is how electronic devices have failed being beyond their safe ambiant working temperature. I have noticed with the dashboard cams they dont like to much heat focused on them.

Of the three units we have the Navman is the worst for losing and picking up signals that seems a common problem worldwide apparently going by the internet. The Unit I use mostly is a Garmin nuvi 30. Great little unit was one the cheapest on the market but not around long. So maybe its a product fault other than seems flawless actually damn good! Tom Tom unit I just find plain and boring.

[kiwi]

Following on I checked the GPS unit on the internet and found out that it needed a critical software update...uh huh that could explain a few things me thinks

While I was there went into the FAQs and found this bit of useful information to ponder for aall those who think the GPS is 100% accurate.

The speedometer on your device may display a different speed than the speedometer in your vehicle.

The speedometer in a vehicle is based on calculations using tire rotation. On the other hand, GPS devices calculate speed based on your GPS position. The accuracy of the speed displayed on the vehicle and GPS device can vary depending upon whether the vehicle's speedometer needs to be calibrated and/or how accurate your GPS reception is.

Please note that GPS devices should be used as a navigational aid and not relied upon for precise measurement of speed.

[Way2go]

Ah well, you'll have to pop down your local gov't surplus and see if you can pick yourself up an inertial navigation system. Just remember to stabilise the platform gyro's before you set off and accuracy will be yours.

[MULLEY]

[docchevron]

I really do love you Marty!