Nuvi 3598-D First impressions / Latest firmware (4.80)

M8TJT · Posted: Sun Jun 29, 2014 4:05 pm Post subject:

Without unnecessarily quoting your whole post. As we all know, the speedo effectively counts the revolutions of the wheel. Here's an example. If at 40MPH the wheel rotates at (say) 100 RPM giving a speedo reading of 40MPH. Now put a 10% circumference smaller wheel on the car. To do 40 MPH the wheel will have to rotate faster (say 110 RPM) to cover the same distance in the same time, thus giving a 10% higher speedo reading. QED ;=)

When you say 'not that accurate' do you mean not as accurate as I indicated or not more accurate than the standard uncalibrated speedo that Joe Public uses?

@cubit. No it wouldn't. The over reading speedo would also give an over-read to the odometer.

walkerx · Posted: Sun Jun 29, 2014 7:10 pm Post subject:

I remember when was at a show in the UK and we were talking about speed cameras, etc. to the police.

We mentioned that the Satnav showed around 4 miles lower than our speedo and they advised that the Satnav will be more accurate than the reading on your speedo, and the reason why they usually allow +/- 10% reading when going through cameras is because the speedo is not that accurate.

Ideally you want your Satnav to show lower speed than what your speedo shows as then you should never get caught speeding. If your Satnav is showing higher speeds then get your vehicle checked out.

Remember though you should always drive appropriately based on road conditions and should never speed.

cubit · Occasional Visitor Joined: Sep 19, 2010 Posts: 26

I'd say the difference is around 1%. So in effect, sod all.
Its not a concern, just an observation.

As to sat have accuracy. This one reads 4mph higher than speedo. My Navigon 3mph and blackvue camera 2mph higher. Again, nowt to worry about.

M8TJT · Posted: Sun Jun 29, 2014 7:29 pm Post subject:

wibbley · Regular Visitor Joined: Feb 08, 2007 Posts: 97

interestingly (or not) I have gizmo which monitors my can bus. Shows all sorts of data, water, oil temp, speed. All of the stuff that gets fed to the ecu.

Now the can bus speed display reads almost identically to my sat nav & the miles covered seem to be the same, however the car speedo reading reads higher than both the can bus and the sa-nav. I know that the spec for speedos (when I built my car) was the speedo may read up to 10% higher than actual but never under. I think car manufacturers deliberately make their speedo read higher than actual, to ensure they comply with legislation and to allow for manufacturing tolerances.

M8TJT · Posted: Sun Jun 29, 2014 9:25 pm Post subject:

I've got one of those.I'll have to give it a whirl and see what it says abt my speed

cubit · Occasional Visitor Joined: Sep 19, 2010 Posts: 26

Kremmen · Posted: Mon Jun 30, 2014 7:21 am Post subject:

it is a known fact that modern car speedos over read - fact. This is a ploy by the manufacturers to ensure that they cannot be blamed when you get a speeding ticket.

My Honda Civic has a digital speedo so it is easier to compare. My first 2007 Civic used to over read by as much as 7 mph at 70mph compared to the SatNav but my 2010 Civic only had a 4 mph max discrepancy (after many owner complaints). My 2013 Civic is slightly better at 3 mph max discrepancy.
However, the mileage figure is accurate.
I've been performing the same journey to the in-laws for decades and that figure is still 104 miles door to door on all cars I've owned.

If you fit a device like a speedo-healer to correct this then I can see the mileage figure being forced to misread
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Viofo A119 V3

M8TJT · Posted: Mon Jun 30, 2014 8:36 am Post subject:

I wonder if they do this so that if you fit winter tyres on the same rims the speedo doesn't then under read due to the deeper tread and thus larger rolling radius.

Kremmen · Posted: Mon Jun 30, 2014 10:15 am Post subject:

Possible

I didn't realise that Winter tyres had a bigger rolling circumference
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Viofo A119 V3

technik · Posted: Mon Jun 30, 2014 10:47 am Post subject:

The digital speedo on my car is always within 1MPH of GPS and those speed warning signs, on both summer and winter tyres regardless of tread depth.
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Metblackrat · Regular Visitor Joined: Mar 18, 2006 Posts: 73

Kremmen · Posted: Mon Jun 30, 2014 12:26 pm Post subject:

I do. Just me but I can't understand how sending data to and from a satellite in space with clouds and possibly trees in the way can be super accurate. I know it probably is but I use the car speedo when passing cameras.
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DashCam:
Viofo A119 V3

cubit · Occasional Visitor Joined: Sep 19, 2010 Posts: 26

M8TJT · Posted: Mon Jun 30, 2014 6:58 pm Post subject:

@Metblackrat.
We seem to be arguing the same thing here.
Wot I said.

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