GPS POI Home POI FilesPOI ToolsPOI MapsGPS ForumSupport
GPS Data Team
ContactFAQSite map

Home > Forums > SatNav Discussion > GPS Speed disparity

Post new GPS POI data or GPS devices related topic in SatNav Discussion forum   Reply to topic GPS Speed disparity Goto page  
 



johmazz2006

GPS: Garmin Nuvi 765, Garmin 3950LMT, Garmin 2455LMT, Navman40, Garmin StreetPilot 3







Post Re: Car Speedo Vs GPS     
Reply with quote

harry3333 wrote:

Does the motorist need to provide evidence on their GPS to prove their innocence?


Don't waste your time trying to use a GPS as a defence mechanism if defending a speeding fine, you will be wasting your time.
View user's profile Visit poster's website





Jfaucett8

GPS: Garmin Nuvi 2555LMT







Post Re: Car Speedo Vs GPS     
Reply with quote

johmazz2006 wrote:

Don't waste your time trying to use a GPS as a defence mechanism if defending a speeding fine, you will be wasting your time.


Wow,

Glad to hear that the GPS evidence won't be accepted as proof. I only hope that it works both ways. Smile Cause I never want a cop to look at the maximum attained speed recorded by my GPS. Chances are the log will show much higher numbers than he/she clocked me. Wink

Emjoy
View user's profile







johmazz2006

GPS: Garmin Nuvi 765, Garmin 3950LMT, Garmin 2455LMT, Navman40, Garmin StreetPilot 3







Post Re: Car Speedo Vs GPS     
Reply with quote

I had that feature pointed out to me by a traffic cop when I made a donation to government coffers. I now delete all logs daily, and obey the speed limits more closely Razz
View user's profile Visit poster's website





william.beck

GPS: 1490T







Post Car Speedo Vs GPS     
Reply with quote

Some good points made in the forum

Changes to wheel & tyer size will make a difference
Mechanical Speedo's can wear
Electronic Speedos can also be out (look at all our clocks)
You get caught over the limit no excuses accepted
In some States the police & radar give no tolerance
Even GPS's can be out (triangulation of the Satellite's relative to the car and terain

Good luck trying to explain your way out Shocked Sad Rolling Eyes
View user's profile





darrenhopps

GPS: Garmin Nuvi 3760 & GPSMAP 76CSx







Post RE speedo vs GPSr     
Reply with quote

In Australia by the ADRs vehicle speedometers cannot read lower than the actual speed. Hence, generally they will read faster than the speed you are travelling, this can be 4-5% or more. Your GPS will generally be more accurate than any speedometer in a vehicle when travelling at a constant speed. As tyres wear the diameter changes so brand new tyres will read a different speed to worn tyres, the vehicle cannot compensate for this, even though the difference between worn and new tyres is a very small amount.
View user's profile





william.beck

GPS: 1490T







Post err on the side of caution     
Reply with quote

Interesting to know the ADR's say the Speedo cant read lower err on the side of caution

Did a quick of my spedo today (out of interest) and sure enough at 100kph there was about a 4 Kph difference. But than I have changed my tyer's from a Bridgestone to a Coopers ATR (slight size variation)

Not too sure what the manufactures actually do but with the two models available there is a 25mm (1 inch) variation in wheel diameter
View user's profile





generalstuff

GPS: Garmin Nuvi660







Post Re: RE speedo vs GPSr     
Reply with quote

To be accurate, the ADRs allow tolerance of minus 1/2 percent to plus 10%.
Invariably the manufacturers aim to be in the the zero to +5% range, although larger errors are not uncommon. The reason for this is the need to cover a range of tyre sizes with a limited number of speedo gear drives. The same effect can be induced by fitting tyres if a different circumference. A lot of young guys don't realise that a 205 x 45 tyre is not the same diameter as as a 215 x 45 of the same rim size - the 45 being a percentage of the width.
View user's profile





alan3333333

GPS: Garmin Nuvi660







Post Speed difference     
Reply with quote

I have noticed a difference of about 6 km/h lower on my Nuvi 660 at 100 on car speedo. With all the speed cameras around I wouldn't trust your GPS speed as being correct. It might be costly.
Previously I had a PDA with navigation and it was exactly the same as the car speedo. It used Co-Pilot Live with an external GPS receiver.
On marine GPS units they calculate speed over ground which is always slightly different to speed through water. Maybe this is why there is a difference.

Anyone have any ideas?
View user's profile





richard-GPS

GPS: Garmin







Post GPS don't do curves     
Reply with quote

Another thing to consider is that GPS's calculate your position every second or so so that it calculates your speed between these points in a straight line, roads tend to curve, so you are actually driving slightly further (so slightly faster) than the GPS thinks you are and the tighter the bends the greater the discrepency, but as billynibbles mentions with the hills this is likely to be a small effect, but all of these small effects add up.
View user's profile





johmazz2006

GPS: Garmin Nuvi 765, Garmin 3950LMT, Garmin 2455LMT, Navman40, Garmin StreetPilot 3







Post speed differences     
Reply with quote

With the accuracy of GPS units down to 3 metres these days and speed of processors etc, don't think a few bends would affect the output readings.
Would much rather believe the GPS over vehicle speedo's these days.
View user's profile Visit poster's website







geenagreen1

GPS: nuvi 760







Post GPS Speed disparity     
Reply with quote

My Nuvi 2460 reads exactly the same as the digital speedometer on my 2007 Honda Civic. Maybe the digital speedos are more accurate than the mechanical versions.
View user's profile





johmazz2006

GPS: Garmin Nuvi 765, Garmin 3950LMT, Garmin 2455LMT, Navman40, Garmin StreetPilot 3







Post Speed indication errors     
Reply with quote

There is no excuse for speedo errors if the original tyres and pressures are used. Problem arises when manufacturers use different profile tyres as on model variants and do not re-program digital Speedo's. Had a Honda 2010 and Suzuki 2012, both sports models with low profile three and both were 8 kph honda and 10kph suzuki out, both above actual speed.
View user's profile Visit poster's website





caesar

GPS: Garmin Nuvi 3790t







Post Re: GPS Speed disparity     
Reply with quote

Legislation in most countries requires the manufacturer to guarantee speedometer readings to an accuracy of only 10%.
Therefore it is obvious that a GPS reading....generally highly accurate....will be far better than a mechanical reading in a car speedometer.
It could be more....it could be less.
Go with the GPS reading.....it could save you a ticket.
View user's profile





life.by

GPS: COMAND SYSTEM; Garmin Nuvi 3790T







Post GPS Speed disparity     
Reply with quote

It is really normal that GPS's speed is slower than the Car's speedo. Manufacturer will increase speedo for safety issue, by contrast the GPS's speed is calculated by satellite based on the vehicle movement. Thus, trust GPS's speed.
View user's profile Visit poster's website





bgtee

GPS: Garmin 3790T







Post GPS Speed disparity     
Reply with quote

I experience the same thing with my Mazda. It is always about 5km more than the GPS. I think this is a good thing as it would mean I will never speed as long as I keep to the speed limit as indicated on my speedo.
View user's profile




Display posts from previous:   
Post new GPS POI data or GPS devices related topic in SatNav Discussion forum Reply to topic GPS Speed disparity
Home > GPS Forum > SatNav Discussion > Discussion
> > >

Goto page  
Page 3 of 5




Jump to:  

 






Permalink: GPS Speed disparity | SatNav Discussion forum (Page 3)