Speedo vs GPS

[slofox]

What I've always wanted to do is to find a friendly policeman at the end of a long straight with a speed gun & do a couple of tests. I would like to ride consistently at 100k on the GPS, then with 100k on the speedo & see what it reads on his speed gun. No matter how good your GPS is, ultimately if there is a descrepency between his reading & your GPS then you'll be gettting a ticket.
I don't think an argument that your GPS is top of the line will go down too well.

Anyone tried it?

Yeah. I found a bunch of coppers playing with their laser guns one morning. I stopped and asked them to ping me at 50k on the clock to check accuracy (it was in 50k zone). They did. Reading was about 6% out. That was on the SV.

It's called hysteresis. They intentionally do it so the retards don't stare at it watching the numbers changing and drive off the road.

At which point it's called hysterics...

And direction, and altitude.........

But yes if you travel at constant speed, with constant direction at a constant altitude - you accuracy CAN be a good as the freq used. Exponential decay outside those parameters.

It was a long flat straight road...

Assuming the error in your speedo is constant with speed ... maybe the error gets worse the faster you go ...

The percentage error was very close to the same at 50km/hr and at 100km/hr...

[wysper]

Seems like everyone is searchng for a more accurate speed reading, GPS or speedo!
I imagine the thoughts are if the cops are going to be ticketing down to 104k then we don't want to loose another 8% in speedo error!

To take another angle
The person your following thats doing 80k and is so lacking in confidence they won't go faster because they've been told Speed KILLS is actually doing 73.6k. LOL!!!

You just gotta laugh its all quite funny what the boys in blue are creating! This scenario must be safer surely we are all going slower now?? LOL!!

and from yet another angle... when you are stopped for a reading of 104kph your speedo might have been indicating 113kph, if it was 110kph then your indicated is pretty much 120kph etc.

So if you travel at 100kph indicated on your speedo, you should be sweet. However if your speedo is actually accurate then your margin of error is significantly reduced.

[sinned]

Assuming the error in your speedo is constant with speed ... maybe the error gets worse the faster you go ...

Some cars have an xKph offset built in. This provides a set Kph error at all speeds rather than a percentage error. The Mazda 3 appears to have a 5Kph offset so reading of 50Kph= 45Kph and 100Kph=95Kph. This contributes to slow driver frustration.

[miloking]

Seems like everyone is searchng for a more accurate speed reading, GPS or speedo!
I imagine the thoughts are if the cops are going to be ticketing down to 104k then we don't want to loose another 8% in speedo error!

To take another angle
The person your following thats doing 80k and is so lacking in confidence they won't go faster because they've been told Speed KILLS is actually doing 73.6k. LOL!!!

You just gotta laugh its all quite funny what the boys in blue are creating! This scenario must be safer surely we are all going slower now?? LOL!!

You know whats even funnier, people driving at 45km/h indicated around town...just because speed limit says "50" so they think "i better be few ks under to be safe that way" all caused by mass hysteria created by police which makes these people think they are in mortal danger on every corner...(sinister man with spinning wheel comes to mind) ...what is that like actual 40km/h hour??? I think olympic sprinters can run at that speed, lol

[Flip]

The electronic spedo on my harley is 3 or 4 kph under at 100 and the old mechanical unit on the old boxer is almost exactly spot on.

[avgas]

Only direction. Your altitude is a function of direction. You need constant velocity, the vector quantity, as opposed to constant speed, the scalar quantity.

Haha yes of course - I was merely explaining it in a way for the poor fellas who haven't done Dynamics.
I still don't like the fact that is does a window average before it does the derivative of the distance though.
But I guess at the end of the day that what you get if you use extraterrestrial telemetry to do such a task.

[avgas]

Assuming the error in your speedo is constant with speed ... maybe the error gets worse the faster you go ...

That would explain "the faster you go the bigger the mess"

[eldog]

The electronic spedo on my harley is 3 or 4 kph under at 100 and the old mechanical unit on the old boxer is almost exactly spot on.

Electronic speedos - are they more accurate than mechanical units?
Or do they just show the same error with figures instead of a needle and a dial?

When travelling on the mway at the signposted speed, I am passed like I am standing still.

Any preferred way of correcting this or do I use a GPS and make an allowance on my Speedo reading

I prefer to be on or below the Hway limit, when travelling in unfamiliar locations (where I might just miss a posted speed limit sign).

[Jeeper]

If you are in Auckland, on SH1 Southern Motorway near the Bombay Hills going south there are marked measured 5 kilometers. Yellow round markers on the side starting from 0 to 5. Maintain a constant speed and measure your time it takes to cover those 5 kilometers. That will give you the most accurate actual speed. There are similar marked kilometers on the SH20 going from Onehunga to Manukau travelling south.

[MarkH]

Electronic speedos - are they more accurate than mechanical units?
Or do they just show the same error with figures instead of a needle and a dial?

When travelling on the mway at the signposted speed, I am passed like I am standing still.

Any preferred way of correcting this or do I use a GPS and make an allowance on my Speedo reading

I prefer to be on or below the Hway limit, when travelling in unfamiliar locations (where I might just miss a posted speed limit sign).

Both my car and my bike have digital speedo readouts, they are both as inaccurate as any other speedo.
I ALWAYS use a GPS to work out what the error factor is, so I can set a speed that is really 100kph instead of just an indicated 100kph. In the car I travel to & from work with, I set the cruise control keeping me at an indicated 110kph, at this speed I don't need to worry about the police, because I'm travelling at a real 100kph.

Since the modern smart phone can provide an accurate speed reading there is no excuse for anyone not knowing what their speed reading really means. Just use the GPS to find out what speed you need on the speedo to travel to maintain a steady 100kph. If it is 110kph then your speedo reads 10% over, 108kph means 8% over, etc. My experience is that the error is quite consistent, so 110kph at a real 100kph means that 55 on the speedo is going to be a real 50kph - the same percentage out throughout the range.

[SaferRides]

Electronic speedos - are they more accurate than mechanical units?
Or do they just show the same error with figures instead of a needle and a dial?

When travelling on the mway at the signposted speed, I am passed like I am standing still.

Any preferred way of correcting this or do I use a GPS and make an allowance on my Speedo reading

I prefer to be on or below the Hway limit, when travelling in unfamiliar locations (where I might just miss a posted speed limit sign).

I've checked the car speedo against the phone and it's high by 4 km/h from 50 to 110 km/h. So I usually keep to the limit +10 and haven't had a ticket.

Dunno about the R1 as I don't have a secure way of mounting the phone yet. But I've had a few cop cars flash their lights when the speedo has been about 115!

[slofox]

If you are in Auckland, on SH1 Southern Motorway near the Bombay Hills going south there are marked measured 5 kilometers. Yellow round markers on the side starting from 0 to 5. Maintain a constant speed and measure your time it takes to cover those 5 kilometers. That will give you the most accurate actual speed. There are similar marked kilometers on the SH20 going from Onehunga to Manukau travelling south.

This is exactly how I calibrated both my GPS unit and also various speedos. After installing a speedo healer on the bike (years ago now) everything measures up perfectly now.

[Jeeper]

The problem with GPS measurements of speed with a lot of units is their inability to adjust for altitude changes (i.e. going up and down hill versus on a flat piece of road).

[F5 Dave]

So you calibrate your Speedo over a fair straight flat bit of ground.

Tank bag or duct tape it.

12 o'clock labs do a cheaper Speedo healer which is small.

TuneECU allows me to adjust my pre13 Triumph for free directly. Always set to accurate that way you don't have to do fast arithmetic when you meet a police person on your trip.

[Hoonicorn]

Your speedo should never under-rate your speed, GPS may not have that same requirement so it could under-read. Speedo + 5% should keep you within the speed limit when the cops decide to go Zero Tolerance.