Using a GPS for WOF purposes - Speedometer?

**Waihou Thumper** · 28th April 2009, 08:51

I have an issue with my speedometer. It works but the display is very dim and sometimes disappears all together. It could be a short and I have pulled everything apart to try and find the issue but to no avail.
I was wondering if my GPS, hard wired and attached to the bike can be used to pass my WOF?

The document obtained from LTSA is a little vague but mentions nothing and only really seems to be concerned with forward speed that has to measured and safety with being obscurred or dangerous etc...

Can anyone enlighten me? Has anybody out there tried this with a testing station or got a WOF with a GPS attached.

I still want to ride the bike until I get it remedied, in the meantime I thought I could use the GPS to pass the WOF.

I have attached the relevent document below for anyone interested in looking. Thanks everyone

**CookMySock** · 28th April 2009, 09:43

Well there are two parts to that ;

1.) You can use anything for a speedo. A bicycle speedo is legal IIRC.

2.) You really have no intention of hard-wiring the GPS in place and leaving there as a speedo do you?

If you get stopped by the fuzz you will have some explaining to do, and your story had better be well rehearsed.

Steve

**davereid** · 28th April 2009, 09:51

Originally Posted by DangerousBastard

Well there are two parts to that ;

1.) You can use anything for a speedo. A bicycle speedo is legal IIRC.

2.) You really have no intention of hard-wiring the GPS in place and leaving there as a speedo do you?

If you get stopped by the fuzz you will have some explaining to do, and your story had better be well rehearsed.

Steve

DB is dead right. I have had to use a bicycle speedo ($29.95) on my CZ, as the original speedo is toast, and un-obtainium.

Bike speedos are calibrated by wheel cicumference, so you can get then perfectly accurate on virtually any wheel.

My speedo claims a top speed of 299 km/hr.. so far the CZ has managed 92, so I must try harder.

For a WOF the speedo must be lit at night.

**Waihou Thumper** · 28th April 2009, 09:53

Originally Posted by DangerousBastard

Well there are two parts to that ;

1.) You can use anything for a speedo. A bicycle speedo is legal IIRC.

2.) You really have no intention of hard-wiring the GPS in place and leaving there as a speedo do you?

If you get stopped by the fuzz you will have some explaining to do, and your story had better be well rehearsed.

Steve

Thanks.
If I get pulled over it wouldn't be for a speedo isssue. The cop would never know it if worked or not, because I am stopped.
It is hard wired and it would be removed etc when left unattended.
I have actully just spoken to the Testingstation and it seems that it has to be a speedo that can register up to 50kph, good working order.
If it is a GPS that can measure speed as it does, the guy seemed to think that it isn't an issue.
If he can see the speed when riding it, then I might be okay. I will in fact have two working speedometers, one of which is a bit hard to see the LED displays.....
Thanks Steve, I will give it a go I think..

**Waihou Thumper** · 28th April 2009, 09:56

Originally Posted by davereid

DB is dead right. I have had to use a bicycle speedo ($29.95) on my CZ, as the original speedo is toast, and un-obtainium.

Bike speedos are calibrated by wheel cicumference, so you can get then perfectly accurate on virtually any wheel.

My speedo claims a top speed of 299 km/hr.. so far the CZ has managed 92, so I must try harder.

For a WOF the speedo must be lit at night.

The GPS does all of that and it is more accurate than the magnet on the circumference of the wheel...It measures the speed and average, maximum and displays current just like the cheap or expensice speedos for bicycles...
It displays at night, back light on permanently, I really cannot see it being an issue here, but could be wrong?

**mujambee** · 28th April 2009, 09:56

Beware that it won't work on tunnels, and may be faulty under heavy forest cover. It will also need some time to fix on satellite after power on.

We've discussed the use of GPS as speedos in a production bike, and they rejected it because of that.

**UberRhys** · 28th April 2009, 10:11

Originally Posted by NZKTM

I was wondering if my GPS, hard wired and attached to the bike can be used to pass my WOF?

I'm sure it can, why not.

Originally Posted by NZKTM

Can anyone enlighten me? Has anybody out there tried this with a testing station or got a WOF with a GPS attached.

One of my scoots has a bike speedo (magnet on the rim set up) and it flys through everytime. Even at the VTNZ nazi warehouse...

**Patch** · 28th April 2009, 10:33

Originally Posted by mujambee

Beware that it won't work on tunnels, and may be faulty under heavy forest cover. It will also need some time to fix on satellite after power on.

We've discussed the use of GPS as speedos in a production bike, and they rejected it because of that.

and some fookn hitler nazi will see it ain't standard and probably make you get it certified - just get the original one fixed

**vifferman** · 28th April 2009, 10:37

My speedo's currently not working (either the sender is 'ted, or the electronic speedo corrector, or there's a loose/broken wire).
I had all the fairings off on Sunday to check it out, and fit new heated grips, but the friggin' thing passed all the tests according to the workshop manual! Then, as soon as I got it out on the raod again, it gave one or two desolutory flicks of the needle, and stopped working altogether.
Gaah! Now I have to take the fairings off again.

It's OK on the open road, as I know that 100km/h is ~5k rpm in 6th gear. However, around town, given I could be any gear, it's a mater of guesstimating, based on experience, other traffic, etc.
I've toyed with using the TomTom (I've used it on the bike before) but it's not weatherproof.

**Waihou Thumper** · 28th April 2009, 10:41

Originally Posted by mujambee

Beware that it won't work on tunnels, and may be faulty under heavy forest cover. It will also need some time to fix on satellite after power on.

We've discussed the use of GPS as speedos in a production bike, and they rejected it because of that.

Is on all the time, it is always fixed to the satellites as a result. The draw of power is as much as your little clock fixed inside the speedo. I would only take it off if resting overnight etc and away from the bike out of view...
I only really want it for the WOF, once I get it I will then look into the original issue. Just cannot afford the labour and testing of the harness or similar.
Being a hand held it really works well under cover of trees, dense bush. Tunnels, yes, that could be an issue but you are only in them for a seond or two unless travelling Mont Blanc or similar...lol

**vifferman** · 28th April 2009, 12:25

Crap! Damn-n-Blarst, and all that.

I am hoping my speedo corrector's fukt, rather than the speedo sender unit. Just rang for a price, and this little gizmo is over $377!!
Of course, it's also, not in stock, so is an indent item, so it'll be "money up front, 3 weeks ex-Japan."
Now here's the ridiculous bit: $377 is ~US$210 (at current conversion rates).
I checked yesterday, and I can get one from several different dealers in The Yooonarted Stites of Mrka for US$72.
Presumably, their Genuine Honda Parts are made in the Philipines, or Kazahkstan or summat, to be only one-third the price.

**BM-GS** · 28th April 2009, 12:43

GPS speed should be accurate as it *usually* works off Doppler from the satellite signals, so no funnies with going round curves, up/down hills, etc.

However, bear in mind that the update is only once a second, and that in town, under trees and in tunnels reception may be a bit iffy.

Dim LCD usually attributable to a circuit-level problem in/near the display itself. New display will be $$$$, poking around behind it to see where the dodgy connection is will be major inconvenience. Your choice...

**MarkH** · 29th April 2009, 10:42

Originally Posted by BM-GS

works off Doppler from the satellite signals

Ummm . . . WHAT????

Unless I have somehow completely misunderstood how GPS works then I am pretty sure it does not use Doppler in any way.

**Hoon** · 29th April 2009, 11:21

As has already mentioned a GPS is unreliable. It is only as accurate as its signal strength and this is affected by rain, cloud cover, tunnels, canyons, high rise buildings and also the inside of a building such as the testing station.

**Hoon** · 29th April 2009, 11:38

Originally Posted by MarkH

Ummm . . . WHAT????

Unless I have somehow completely misunderstood how GPS works then I am pretty sure it does not use Doppler in any way.

Some do but only for correction. Basic position is calculated by the usual distance triangulation thing but is adjusted for the movement of the satellites and rotation of the earth.

To get the best accuracy these days they take everything possible into account including time dilation due to the satellites high speed and time slowing down (einsteins theory of relativity).