Speedo Check.

Delboy · Member

RE: Speedo Check.

Smokeydk · Guru

PeterD wrote:
You don't have to rely upon good satellite signals. You use the GPS/navigator once whilst you have a good flat road and a clear sky. Once you have these conditions you calibrate your speedo. Once you have calibrated your speedo there is no need to use the navigator again to check speeds.

Peter........how do you calibrate speedo.....I know mine is out by 11kph at 100kph..according to GPS...also my GPS said I was in a 50kph zone...while in a 100kph zone on a dead flat 80klm road.on a 40 deg day no cloud

My GPS is on a bracket stuck on middle of dash of front screen...

Delboy · Member

No easy way to adjust your speedo unfortunately. You may want to confirm tyre sizes are factory standard or discuss with your dealer. Re the 50kph zone warning. Gps data in AU is relatively low quality, information such as speed camera and zone alerts is often flawed. Check for a software update if your GPS offers this facility. With some systems you may need to pay for the update even for the zone information on others this is freely available on the web.

Cupie · Guru

03_troopy wrote:
Delboy wrote:
I assume we will disagree on this point but... I was keeping the explanation simple as detailing all the variables that effect RF propogation through the atmosphere is well beyond the scope of this thread. You are correct drop outs will be higher and inaccuracy increase as reacquisition on each satellite occurs but the critical timing the GPS system is dependent on will also be effected.
No worries delboy. As being involved with RF transmission & reception, radio navigation systems, radar and in more recent years GPS nav systems etc in aircraft for close to 40yrs I tend to be a bit pedantic about this topic and leap on minor inaccuracies such as this a bit more than I should. Sometimes it's easier just to let it go I suppose. The point I was trying to make though, was that the signal won't arrive any slower. It just may not be available at times and it may take longer for the GPS unit to be able to give any meaningful information. Correct mounting of the unit can help lessen these effects, by having any metal from the car body shielding the GPS as little as possible. I Hope this helps.

Why don't you guys call a truce & if you like debate the issue via PMs et.al.

For my part, I will just un-subscribe to this thread.

Like you guys, I too have a technical background in Army signals & telecommunications ... but in my dotage have not sufficiently kept up with current technology, so I can't even mediate the the discussion.

Enjoy your common interests & not dwell on the differences.

03_troopy · Guru

Cupie wrote:
03_troopy wrote:
Delboy wrote:
I assume we will disagree on this point but... I was keeping the explanation simple as detailing all the variables that effect RF propogation through the atmosphere is well beyond the scope of this thread. You are correct drop outs will be higher and inaccuracy increase as reacquisition on each satellite occurs but the critical timing the GPS system is dependent on will also be effected.
No worries delboy. As being involved with RF transmission & reception, radio navigation systems, radar and in more recent years GPS nav systems etc in aircraft for close to 40yrs I tend to be a bit pedantic about this topic and leap on minor inaccuracies such as this a bit more than I should. Sometimes it's easier just to let it go I suppose. The point I was trying to make though, was that the signal won't arrive any slower. It just may not be available at times and it may take longer for the GPS unit to be able to give any meaningful information. Correct mounting of the unit can help lessen these effects, by having any metal from the car body shielding the GPS as little as possible. I Hope this helps.
Why don't you guys call a truce & if you like debate the issue via PMs et.al.
For my part, I will just un-subscribe to this thread.

Like you guys, I too have a technical background in Army signals & telecommunications ... but in my dotage have not sufficiently kept up with current technology, so I can't even mediate the the discussion.

Enjoy your common interests & not dwell on the differences.

Sorry you saw the conversation that way cupie. It was more a case of explaining why sometimes we don't get the best performance out of some of the equipment we purchase and suggesting how to improve performance.

PeterS · Senior Member

I will not get involved in the GPS arguments but most Auto Club (RACV

PeterS · Senior Member

hmmm dont know what happened to rest of post! NRMA RAA etc technical depts have roll on dyno for testing speedo and will refer you to instrument repairer if required.

deverall11 · Guru

Ladies and Gentlemen,
Two things:
1) the discrepancy in the speedo may NOT be the same across the range of speeds indicated. 10% @ 100kph, 5% @ 80kph.
2) I have a scangauge in the tug. The dial reads 100kph, scangauge reads 95kph and the gps reads 95kph.
Now, the scangauge gets its information from the ECU, the same place as the dial.
Food for thoughts.
Larry

Legendts · Senior Member

dorian wrote:
My 1996 Toyota Camry and Aldi GPS display the same speed. I'm curious as to how some speedos can be 15% inaccurate.

Are people using lower profile tyres? Have the vehicle manufacturers installed the wrong speedo gear in the gearbox?

Dorian, when new my 200 series was around 5kph under actual speed but since changing tyres to a slightly higher profile it is now accurate. I believe manufacturers are permitted a 10% error, or used to be. Pity the speed cameras don't too eh?

SnowT · Guru

Me I use the GPS to set my speed.. on cruise control..

I'm also very interested in the Dash cam's that include a GPS so that you can prove that you were doing the right thing at the time of any accident..

so yes I do believe in the speed I get off the GPS..
- Most GPS give you the option to see how many satellites you are in your sky at any time..
No I can't tell you hoe to find that info for all GPS's

Juergen

Plendo · Guru

I often travel with work, and when I pick up a hire car I use an application called speed view to check the accuracy of the speedo, as it makes a difference when you have a 2 to 4 hour drive ahead of you. Speed view exactly matches my Hema HN6i in my car, so I believe it is reasonably accurate.

I find massive variations in some cars, the worst I have found were a couple of Commodore wagons I hired from Newcaste airport, where they were indicating 112 & 113 kpy respectively at exactly 100. Most Commodores are around 108/9, Falcons are typically a little closer, around 105, Toyotas vary between 103 and 107. A recent Audi was a bit optomistic as well at 108.

I have not seen anything closer than 103 (a Toyota, and a Falcon).

The other interesting one is the average fuel consumption displayed on the dash, it is typically an optimistic work of fiction.

brian · Guru

I think you will find that the tendency for speedos to read slightly high is a carry over from European traditions in an attempt to reduce speeding fines. This is borne out by the fact that it is only the speedo that is incorrect, the odometer and other information that is gathered from the same sensor is generally very accurate. Also be aware that a gps speed reading is only accurate when consecutive readings are taken with the vehicle travelling in a straight line. Any gps speed readings shown on a winding road or on a curve will be lower than your actual speed, the degree of difference will depend on the update rate of the gps processor and the frequency of the changes of direction of the vehicle.

PeterD · Guru

brian wrote:
I think you will find that the tendency for speedos to read slightly high is a carry over from European traditions in an attempt to reduce speeding fines. This is borne out by the fact that it is only the speedo that is incorrect, the odometer and other information that is gathered from the same sensor is generally very accurate.

There was a change in the accuracy requirements for speedometers early this century. I'm not sure of the exact date. The accuracy was expressed in +/- figures and the speedo had to be fairly accurate.

The new conditions were introduced as speeding fines were being successfully being challenged on the basis that their speedo reading was low and they were not aware of the fact. The current situation is that vehicle manufacturers are not allowed to produce vehicles with low reading instruments. To ensure that they don't speedos now read higher than they did under the old regulations. The JPG below is a copy from Vehicle Standard (Australian Design Rule 18/03 Instrumentation) 2006.