Tested my speedometers versus GPS

[merv]

So far I have checked out the speedos on our bikes and one of our vehicles versus the speed reading from a Garmin GPS and have found that the most accurate is the Toyota being less less than 2% optimistic showing 110km/hr versus 108. Next best was surprisingly my WR250 with its tiny little enduro speedo with 110 versus 106. Then Mrs merv's DR650 110 versus 104 and 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.

[WINJA]

so far i have checked out the speedos on our bikes and one of our vehicles versus the speed reading from a garmin gps and have found that the most accurate is the toyota being less less than 2% optimistic showing 110km/hr versus 108. next best was surprisingly my wr250 with its tiny little enduro speedo with 110 versus 106. then mrs merv's dr650 110 versus 104 and 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.
how acurate is the gps?

[froggyfrenchman]

youre lucky, at 100 on the speedo, im doin 115!

[merv]

how acurate is the gps?

I'm taking it that its as good as you are going to get if you ride at a constant speed for a while.

[Pixie]

On the new Bandits a displayed 220 kmh is a true 194 kmh

[Swoop]

(EDIT - Response to deleted email about caps locks, deleted.)

[madboy]

I know when I had mine at the flying 1/4s the speedo was reading 270 into the timing zone and 277ish coming out. Actual average speed was 249-something.

Following a cop one night (albeit a bit closely) down the mway I could tell from his radar readout that he was travelling at about 100-102 while I was sitting behind him showing 102-105 on the speedo.

I need to find a GPS I think ;)

[merv]

Mrs gave me the Garmin unit for Xmas - nice of her eh! Fits nicely on the front of the VFR - use the car mounting for that and on my WR I have a "bike" mounting which basically clamps onto the cross brace of the bars. Here's a pic.

[mattt]

I'm taking it that its as good as you are going to get if you ride at a constant speed for a while.

These a bloody accurate, as they are constantly tracking satellites. Also the faster you go, the more accurate they are.... officer...
I had a garmin geko - stood in the back lawn, as soon as i even lent towards the house it picked up a reading of .1kph. Quite useful for missile tracking too apparently....

[LB]

Merv my petal - were you travelling north on the VFR on Friday late afternoon, around Otaki or thereabouts?

Mrs Merv buys great pressies!!

[merv]

Merv my petal - were you travelling north on the VFR on Friday late afternoon, around Otaki or thereabouts?

Mrs Merv buys great pressies!!

Hi Lynda, Happy New Year.

No, on Friday me, Mrs and Bro went to Castlepoint and back - had a great ride on a nice sunny day but were surprised no other bikes were on the road. That photo I attached here was taken at Masterton. Today just me and Bro did a nice little local jaunt out to Waikanae, over Akatarawa Rd, then to Te Marua up Plateau, Whitemans Valley, Blue Mountains Rd then through the Hutt out to Wainuiomata Coast and back and then home. My dirt bike background makes me love all the little tight roads even on the VFR.

The GPS Mrs got me was as recommended by your work buddy Richard and she got it when we were in ChCh from the guy he put us on to. The key is the local maps he supplies based on the NZ Topo series. Works well but there are some old bits in it. One classic was heading out from Martinborough to Bell Tea corner and when I turn I'm riding in the paddock according to the map, so at some stage the road must have crossed an old bridge a few hundred metres away from the existing turnoff. GPS is marine version that you can swim with for at least an hour according to the salesman so perfect for mounting on the bike.

Hey looking forward to our mate John putting on the next Capital Coast so I'll try the GPS on that on the WR.

[Mental Trousers]

how acurate is the gps?


Source - http://en.wikipedia.org/wiki/Gps
Satellite Navigation Systems can be used for determining one's precise location and providing a highly accurate time reference (http://en.wikipedia.org/wiki/Time_transfer) almost anywhere on Earth (http://en.wikipedia.org/wiki/Earth) or in Earth orbit (http://en.wikipedia.org/wiki/Earth_orbit). The accuracy of the GPS signal itself is about 5 meters (16 ft) as of 2005 and has steadily improved over the last 15 years. Using differential GPS and other error-correcting techniques, the accuracy can be improved to about 1 cm (.4 in) over short distances.

It's pretty damn accurate alright.

[Highlander]

Good on ya Merv.
I haven't done the CB yet, but past one of those Police sign board thingies, said I was doing 45 with Spedo indicating smack on 50. :Police:
Will slip the GPS into the tank bag map pocket and go for a burl. :scooter:

Our Odyssey (yup the cage is a honda too) is a little optimistic 110 on the Spedo is 105 on GPS. Good to have a reference.

[NordieBoy]

Always wondered why one Nordie felt far more stable around corners at 100kph than the other.
I put it down to the less stable one having a slightly bent frame.

GPS says the stable one was only doing 90kph.

[scumdog]

It's pretty damn accurate alright.

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.

[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 :headbang:

[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