In another topic it was mentioned that a speedo could have up to 10% error (ie 70 mph is actually 63 mph), but not the other way round. This leads me to think about how accurate are the odometers. Are these 100% accurate or do these have a built in error of reading like the speedo. Could this mean a 70,000 mile reading is actually only 63,000 miles?
I am sure someone knows the answer.
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Not sure about the modern day digital odemeters, but the old ones were mechanical and driven by gears, so there *shouldn't* have been any error factors with the odometer. A lot of the speedo inaccuracy was down to that there was a magnetic disc which was driven by the speedo cable, an air gap, then a steel disc on the back of the speedo needle. A lot relied on how strong the magnet was, what resistance there was on the speedo needle shaft, and whether the return spring was worn or not.
I imagine with modern day electronics, most of the inaccuracies have been ironed out.
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All the Pugs I have owned (quite a few) have over-read mileages by anything from ½ to 4 percent. This will clearly vary somewhat with the tread depth on your tyres, and more obviously with whether the tyres fitted are the size the odometer was intended for. I don't know if this is because the car was designed for kilometres, and the conversion gearing was not quite exact [shouldn't be any discrepancy with electronic meters of course].
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In three different makes of cars over the last three years over the same journey taken one a week the odo read between 66.3 and 66.5miles.
I suspect the differance related to not taking the same line on the road.
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All the Pugs I have owned (quite a few) have over-read mileages by anything from ½ to 4 percent. This will clearly vary somewhat with the tread depth on your tyres, and more obviously with whether the tyres fitted are the size the odometer was intended for. I don't know if this is because the car was designed for kilometres, and the conversion gearing was not quite exact [shouldn't be any discrepancy with electronic meters of course].
How do you know?
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On a recent 100 mile trip, zeroed and monitored by GPS, the RF odometer was more then 99.9% accurate.
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If you have a modern(ish) car then the analog dials are controlled by electronics. On Ford's for example, you can enter diagnostic mode and do all sorts of checking, e.g.
- Gauge check moves all analog gauges around from min to max... proving the read out shown is controlled by the car and not connected to anything like the fuel gauge, temperatures, revs or speed.
- The speed (mph or km/h) digital read out changes in real time and is closer to real mph (e.g. measured by GPS) than the analog readout. The analog one has some sort of inertia associated.
All I know is from a GPS measurement there is definately some margin for error. Around 30-50mph it's quite accurate but get to 70mph and beyond and it is not so accurate.
If you assume the dials are accurate though and say travel at 80mph then you'll not likely be stopped/fined because you're below 79mph.
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Forgot to add that whilst the speedo has some error (deliberate?) the mileometer seems pretty accurate measured by GPS etc.
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Thanks Guys
I think the next time I do a long run on a motorway I will check the roadside mile markers and compare it to my odometer as I do not have the benefit of a GPS.
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Dont do that Mr Artful, the motorway roadside "mile" markers are in kilometers.
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Hello RF
Just shows you can still learn something every day. I always thought they were mile markers, not kilometer markers.
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