The Speedometer in my car shows 10% faster than actual road speed when compared to the portable GPS.
So 60mph on dial is actually 56mph, 70 is 63.
This HAS been discussed in many threads here, and I HAVE read all of them. I've started this one though because I'm asking:
Is it likely the mileometer is ALSO inaccurate?
Has anyone done a, for example, 100 mile run calculated by GPS or somesuch and compared it with the odometer?
If it's also out, then issues to be considered:
Service interval of 12,000 miles.. Could be done at an indicated 13,200?
Claiming Mileage from business/ government is inaccurate?
Calculated MPG figures would be optimistic?
When advertising Mileage on a car as "done 80,000 miles!" could mean "actally done 72,000 miles but shows 80 on clock" (Buyers benefit)or even "shows 88 on the clock on the clock, but has really done 80k" (Sellers advantage)
hmmm. Any thoughts? How to test the odo accurately?
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Hmmmm, good question.
All i know is that to do the 92 miles as indicated on my odometer between Loughborough and Watford in an hour, i need to be going at 100mph indicated on the speedo.
Therefore i'd assume they are driven by two separate mechanisms?
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So, that means that when someone is snapped by a speed camera, at, say, 95mph on a motorway, their speedo is actually reading about 107?
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If my car were to be driven at 95, the speedo would show 107.
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Adam
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All i know is that to do the 92 miles as indicated on my odometer between Loughborough and Watford in an hour, i need to be going at 100mph indicated on the speedo.
And are you? ;-)
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L\'escargot by name, but not by nature.
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Who, me?
'Course not, purely hypothetical you understand
;-)
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Is it likely the mileometer is ALSO inaccurate?
And even if it isn't, who's to say that the rolling radius of the tyres is as assumed by the car manufacturer? What about the effect of over/underinflation?
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L\'escargot by name, but not by nature.
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I don't bother with these service interval indicators.
Despite my greying hairs, I still think I am a better judge of when my car needs a service than a computer.
And I don't like long service intervals anyway.
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I have checked speedo and odemeter against GPS. You need to take care when measuring distance on GPS as its a straight line between measurement interval points.... BUT
On a straight road (M4) over 100 miles, the odometer on the car was 100 miles and the GPS was 99.9 miles. Good enough.
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If your car decides its self when it needs a service it doesn't really matter if the odemeter is out, even by 80%.... and if its mileage based then as you say you would be getting the service early, which is a good thing for the engine!! :-)
BTW, My Mondeo reads 74mph at a GPS 70. At an indicated 150mph (down one of the long hills near Frankfurt on A45) the GPS reads 142, which means its quite accurate. At GPS 30 though, speedo is reading 35.
This means the acuracy changes:
Indicated...
30mph = 14.2%
70mph = 5.4%
150mph = 5.3%
When the engine is turned of the speedo reads 0, as soon as you turn the key to 'ingition' position, it flicks up to 2mph.
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Neil T
Mondeo Ghia TDCi 130 Estate, SEAT Toledo 20VT Sport, Various Montegos...
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>Has anyone done a 100 mile run calculated by GPS or somesuch and compared it with the odometer?<
I have always assumed that the 100-metre posts on our motorways are fairly accurate (ignoring the possibility that the odd one is misplaced, which should be negligible over 50km). As I have reported before, Pug odometers read anything between 1 and 4 % over, in my experience. My current 306 (my first with a digital readout) reads +1.4%. Tyre size could have an effect, especially if a non-standard size is fitted; a new tyre could be about 2% 'bigger' than a nearly-bald one.
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