why dont my speedometer and my GPS read the same speed?
If I am doing 90 km/hr on the speedometer my GPS says I am only doing 80?
That I can live with! But the nagging question is what does traffic police radar work on, my speedo or my GPS?
Any insight?
Your GPS is likely to be more accurate. If you drive by the speedo in the car you should be safe from police radar as you will be driving under the speed limit. Car speedo's are often not accurate.
Tony
gxr (17th January 2011)
Ive also noticed that my gps says im slower than the speedo
and the same in the bosses car x10ks slower
roofy
Hi GXR and Ynot,
Not wanting to step on your toes Ynot as you are the guru when it comes to the mechanical stuff. I just wanted to add to your answer above.
Car GPS devices are, in general, accurate to 1 - 5 meters so it will be more acurate more consistantly as it relies on mathematical equasions to show your current speed. Where your speedo relies on a mechanical system to show your speed on the Speedo. If any part of the drive train has been modified then you will need to have the speedo re-calibrated. Have this done by the manufacturer or one of their autrhorised service agent.
Here is some info on how a speedometer works that may help you, and us, understand what to look for. http://www.explainthatstuff.com/how-...ter-works.html
Cheers,
Rob
Just about to jump into my next Patrol. A 2001 GU II TB45E .
WARNING!: Do not ever use a towball as a recovery point. They are not rated and can become a deadly projectile during a recovery if they snap off, and they have done so with tragic results in the past.
Speedo readings (not Odometer just the Speedo) are required by ADR's to overread the cars actual speed by between 0 (IE be dead accurate) to up to 10% of reading + 4 KPH. They cannot indicate the vehicle is travelling slower than actual by even 1/10th of a KPHOriginally Posted by gxr
EG if your actual speed is 80 KPH then the Speedo is required to indicate between 80 and 92 KPH.... at 100 KPH actual indicates between 100 and 114 etc. Most manuf will set 'em at around 7 ish to allow for punters to go up one size in placarded tyres and still be OK.
GPS speed is accurate to + / - 1 KPH at least 99% of the time IE if it says you are doing 80 you will be doing between 79 and 81.
GPS is equally as accurate as Radar or Lidar in the Lab as they all work on Doppler Shift of the radiated frequency BUT the GPS signal has to travel about 17,000 K's so is subject to some atmospheric and reflection errors as opposed to the Radar/Lidar which is only several hundred metres travel but has other problems to compensate for.
Dolphins are so smart that within a few weeks of captivity, they can train people to stand on the very edge of the pool and throw them fish.
gxr (17th January 2011)
I've noticed this as well. At about 50kph it's fairly accurate, but by 110kph, the GPS is only showing 100kph.
1981 Nissan Patrol MQ SWB, 3.3TD, West Melbourne.
Put it simply, Many people change the rolling circumference of their tyres from factory set up to way bigger, and never have their speedos recalibrated. Therefore speedo reads incorrect.
Getting Older Is Unavoidable, Growing Up Is Optional!
Yep, but need to keep in mind that bigger rolling circumference makes the Speedo read under not higher.
What going from 31's to 33's or bigger does do that is often not taken into account is throw the Odometer out when working out Fuel Consumption and Service intervals.
Dolphins are so smart that within a few weeks of captivity, they can train people to stand on the very edge of the pool and throw them fish.
I knew when I was typing that, I had it back to front, but, it was the principle I was trying to state that time.
IF you change wheel circumferences, get speedo calibrated.
Getting Older Is Unavoidable, Growing Up Is Optional!
sometimes the speedo drive gear at the gearbox end has an incorrect ratio. A cynic might say that if the Ks click over on the odometer more quickly than they should, that is a good thing for those who offer a warranty. I have seen this with new factory fitted tyres and rims in a GQ with 16s.
In the case of my Mav, however, I suspect it is because it was set up for 750 R16s and changed in aust to 10rs
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