copilot/ navman gps speed readings..how accurate are they?

Submitted: Wednesday, Jan 21, 2009 at 17:11
ThreadID: 65310 Views:6320 Replies:12 FollowUps:6
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Hi all,
How accurate are the speed readings on these things I have a Mypal A696 with Copilot 7 nav software.

It is 6kph slower than the speedo in the gutlux at 100kph.

Has anyone checked with a police radar or some other method?

Cheers
Dave
Cheers,
Dave
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Reply By: Member - Troll 81 (QLD) - Wednesday, Jan 21, 2009 at 17:30

Wednesday, Jan 21, 2009 at 17:30
Trust the GPS don't trust your speedo
AnswerID: 345391

Follow Up By: Member - Tour Boy- Wednesday, Jan 21, 2009 at 17:31

Wednesday, Jan 21, 2009 at 17:31
I suspected the speedo was out as everyone sits up my clacker but I just want to be sure.
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Dave
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Reply By: Member - Troll 81 (QLD) - Wednesday, Jan 21, 2009 at 17:32

Wednesday, Jan 21, 2009 at 17:32
If you have changed your tires then it might be out but the GPS will be spot on
AnswerID: 345392

Reply By: Member - Tour Boy- Wednesday, Jan 21, 2009 at 17:36

Wednesday, Jan 21, 2009 at 17:36
It's on my work gutlux, current model, I have wider tyres on the 6 inch rims but the speedo reads 6km higher as though I have smaller dia tyres. It didn't seem to change from the original tyres.
Cheers,
Dave
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AnswerID: 345393

Reply By: Member - Paulnmissus (WA) - Wednesday, Jan 21, 2009 at 18:01

Wednesday, Jan 21, 2009 at 18:01
Hi
I have 3 gps of various types all very close to each other in terms of accuracy, speedo on the Toyota is another matter altogether speedo is 5km slow even tested against ground marks they used to use for aeroplane mounted speed trap. Most vehicles have some degree of inaccuracy.
AnswerID: 345398

Reply By: garrycol - Wednesday, Jan 21, 2009 at 18:03

Wednesday, Jan 21, 2009 at 18:03
There is a slight lag in GPs speed so if accelerating or slowing down will be slightly out but if travelling at a steady speed it will be 100% accurate.

Garry
AnswerID: 345399

Reply By: Member - Vince B (NSW) - Wednesday, Jan 21, 2009 at 18:16

Wednesday, Jan 21, 2009 at 18:16
Hi Dave,
I checked my speedo with my Navman & a hand held GPS.
Both showed that at 100 kph my speedo was showing 106kph.
I know what I will trust in future LOL.
Cheers.
Vince
AnswerID: 345403

Reply By: Member - Graham H (QLD) - Wednesday, Jan 21, 2009 at 19:44

Wednesday, Jan 21, 2009 at 19:44
Most car speedos are optimistic only differing by how much.

Just like their performance claims and petrol consumption HA HA
AnswerID: 345408

Reply By: Dave B (NSW) - Wednesday, Jan 21, 2009 at 20:36

Wednesday, Jan 21, 2009 at 20:36
I think most vehicle speedos are fast by about 5-10%.

That way when you work out your mileage for fuel and tyres etc. you get a figure much better than reality.

In theory, your pretty happy, well happier than if you knew the right mileage anyway.

It also means that your servicing at the dealers comes up quicker so they can ream some more money out of you a bit more often.

Dave
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AnswerID: 345415

Follow Up By: Member - Mike DID - Wednesday, Jan 21, 2009 at 21:05

Wednesday, Jan 21, 2009 at 21:05
Just because the Speed is out doesn't mean the odometer is out - they are different calibrations - even for the old cable-driven ones.

I usually find the speedo indicates high, but the odometer is accurate
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Follow Up By: Dave B (NSW) - Wednesday, Jan 21, 2009 at 21:15

Wednesday, Jan 21, 2009 at 21:15
I am not sure about that Mike, you might be right.

But, why would they make one reading accurate, and the other reading so far out?

Is it a technology thing that they haven't been able to get right, or could there be some other reason?

Dave
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Follow Up By: Ken - Wednesday, Jan 21, 2009 at 21:34

Wednesday, Jan 21, 2009 at 21:34
Mike, as I understand it electronic speedos work by counting the number of tailshaft revolutions and are calibrated taking into account tyre diameter and diff ratio. X number of pulses = X numbers of km. Speed is derived from this distance vs time which is taken from an internal clock. There should therefore be no differing accuracy between the speed indicated and the distance indicated unless the manufacturer chooses to inflate the speed indication for reasons of safety factor in speed zones or to artificially inflate performance.
I have never checked the distance readings between a GPS and the speedo but it could be interesting to see the result given the speed readings vary considerably.
Ken
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Follow Up By: Member - Oldplodder (QLD) - Thursday, Jan 22, 2009 at 10:18

Thursday, Jan 22, 2009 at 10:18
Noticed a difference on the Paj between the speedo and the odometer.

I have bigger tyres than stock by +10%.

Speedo now reads 98 at 100 true.
Odometer now under reads by 5%, i.e. 95km on the dial is 100k true.

So there is a 3% difference between speedo and odometer.

Checked by GPS a number of times over the years.

Difference could be due to the two sizes of tyres supplied in the Paj range at the time. 235/75/15 (29") and 265/70/15 (31"), so speedo and odometer set as a compromise towards the larger tyre sold on the more common GLS model. All still within the specs of the ADR.
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Reply By: Gronk - Wednesday, Jan 21, 2009 at 23:44

Wednesday, Jan 21, 2009 at 23:44
Your speedo is always optimistic because it's illegal for the manufacturers to have them read slow....( and would't people complain if they were getting booked all the time !! )
They are allowed to be up to 10% fast.....anymore and you are entitled to get them to fix it ....only on new cars of course...
AnswerID: 345457

Reply By: Sigmund - Thursday, Jan 22, 2009 at 07:09

Thursday, Jan 22, 2009 at 07:09
At 110 kph indicated my Forester is about 5-6 kph over the actual acc to the GPS, and 9 kph over acc to the speed check display on the Hume Highway north of Melb.

In the 'fine' state you can be done for 3 kph or more over the limit.
AnswerID: 345464

Reply By: Member - Tour Boy- Thursday, Jan 22, 2009 at 09:13

Thursday, Jan 22, 2009 at 09:13
Thanks for the replies guys,
another reason they might want to make the speedos run over is the 100,000km warranty actually runs out after 95,000km

Cheers
Dave
Cheers,
Dave
2010 Isuzu FTS800 Expedition camper
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Had 72 cruisers in my time

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AnswerID: 345477

Follow Up By: Robin Miller - Thursday, Jan 22, 2009 at 10:43

Thursday, Jan 22, 2009 at 10:43
They are usually seperately calibrated Dave, as the odometer is required to be more accurate and maintain its accuracy regardless of speed.


Robin Miller

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Reply By: StormyKnight - Friday, Jan 23, 2009 at 11:57

Friday, Jan 23, 2009 at 11:57
Yep GPS is 100% correct...

Worst car I drove for speedo error was a Mazda 6...

I was wondering why trucks where passng me when I was doing an indicated 110km/h on the freeway. Turned out to have error of around 11%...i.e. it indicated 110, i was doing 100!

worse was when I was doing an indicated 100, I was only doing 89!

Mazda 6 is a very safe car though & real good on the fuel (Diesel 6.4l/100km), now I know why :)
AnswerID: 345629

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