Tested my speedometers versus GPS

[Highlander]

My GPS gives elevation, altitude, rate of climb etc. as part of the readings so I assume (and it is an asumption) that distance travelled would include the vertical component.

Doing a check on relatively flat, straight stretch of road would give pretty good reading though I would expect.

[Fatjim]

Some of the bike speedos work quite well, make sure you get one that reads over 99kph. Quite popular when changing you gearing.

http://www.burniemorgan.com/firestorm/sigma.html

[merv]

If, (hypothetically) you were to go down one side of a BIG dip and up to the top of the other side would it (a) measure the actual 'road-surface' distance you covered or (b) measure in a straight line from the top of the first rise to the top of the second rise??

Likewise in a tight twisty section of road?

Only used a gps while hunting - different situation.

As per Highlanders reply the GPS does measure 3 dimensionally, but that is provided it has locked on to enough satellites and it tells you on the display whether its doing 2D or 3D. I'm impressed with it and enjoy using the maps while I'm riding and as I mentioned earlier its quite funny when you ride where the road has been altered. For those that ride it you can guess how funny it looks leaving a track on the map through the Kaitokes now. Each ride I've done I've downloaded the recorded tracks taken before I've deleted them from the unit so I can browse them on the PC. All a bit of a novelty at the moment as you can imagine.

[pete376403]

So far I have checked out the speedos on our bikes and one of our vehicles ... worst is my VFR 110 versus 102. The VFR has a nearly worn out rear tyre so a few mm of extra tread would fix that a bit but only minimally. So now I know how fast I can go on the speedos and stay at 109 or less or whatever the cops think the tolerance should be.

Is the speedo driven from the rear wheel on the VFR? I thought only shitty old brit bikes did that.

[FlyingDutchMan]

I've made my own speedo, and its accurate to +-1km/h. I've gone past quite a few cops at 108-109 and they've done nothing (the old speedo would have read some where around 125km/h).

[MisterD]

I wouldn't particularly trust a GPS for instantaneous speed, I've seen units which will show you moving while you're standing still. A lot of manufacturers for in-car stuff are looking at incorporating info from ABS wheel-monitoring to increase accuracy....

[merv]

Is the speedo driven from the rear wheel on the VFR? I thought only shitty old brit bikes did that.

Yeah I guess most Jap road bikes are like this now they are electronic or some such thing driven of the gearbox/engine with no cable drive. All the dirt bikes we have are still cable driven off the front wheel.

Interestingly what I found on the trip in the Wairarapa last week is that while the WR250F had the most accurate speedo of all our bikes, its odometer seems abysmal being about 25% slow. I'll do further tests with it, but it probably explains why I'm always bitching on adventure rides that my odo is way off compared to the route sheet distances. Now how could Yamaha do that? Getting the odo right you'd think would be the easy bit seeing its a simple gear ratio thing between wheel turns and how many times before you click a 10th of a km over.

This made one thing become clear - when I first bought the WR and was running it in before the Pukemanu ride in 2004 I was worried about fuel range as it would go on reserve at around only 130 - 140km. LB's lovely husband told us at the run how far the longest distance was between gas stops and I thought "could be tight, but let's hope we are OK". Well it turned out I never had a problem and on the last leg, which was the longest, I get back to Martinborough no worries and then continued onto Greytown where we were staying. My Bro on his DR350 went onto reserve, my WR didn't need it. Now with the GPS I have realised I'm probably doing 25% better on fuel than I thought too. There are some bonuses in life after all.

[marty]

If, (hypothetically) you were to go down one side of a BIG dip and up to the top of the other side would it (a) measure the actual 'road-surface' distance you covered or (b) measure in a straight line from the top of the first rise to the top of the second rise??

Likewise in a tight twisty section of road?

Only used a gps while hunting - different situation.

if it has aquired 4 satellites it should give altitude information, which will also give speed in a dive/climb. 3 sats will only give linear speed, so there will be some cosine error if that is the case. tight & twistie shouldn't make any difference if it's an accurate machine

[sAsLEX]

Quite useful for missile tracking too apparently....

Not really they dont update fast enough and dont include attitude and roll without multiple aeirials........now what would be good is a MEMS INU utilising Adaptive Kalman filters GPS updating .....now who would be making one of those at uni

[sAsLEX]

if it has aquired 4 satellites it should give altitude information, which will also give speed in a dive/climb. 3 sats will only give linear speed, so there will be some cosine error if that is the case. tight & twistie shouldn't make any difference if it's an accurate machine

Pretty sure three will give you altitude, as its using some rather tricky radio waves to determine your distance from those satillites, so if you have three you can determine your position in xyz, am studyin the GPS signal decomposition at the mo and it is quite intersting for communicationy type people