Can anyone advise me on a way to check my odometer ? I'm suspecting it under-reads, due to my model having larger than std wheels + not very low-profile tyres.
Thanks
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Roger
Checking the odometer is more difficult than checking the speedo over one of the measured miles you see beside motorways. You're right that larger tyres will make the odometer under-read. How about check over a reasonable distance against Autoroute computed distance?
As the larger tyres will make the speedo under-read this may be worth a check also.
An alternative is to ring the tyre makers and get the revolutions/mile data for both tyres which will enable you to calculate the variation.
Regards
john
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Roger,
Try comparing readings with distances given on motorways for next Services ("Services 1 mile and 26 miles" etc), as these are usually more accurate than other poit-to-point distances in my experience.
Regards, Adam
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Adam
Good idea - they are certainly better than 'normal' road side distance signs.
regards
John
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Why not contact your local Traffic Police dept. and ask them where their ' Measured Mile' is. This is an exact mile and used to calibrate speed detection devices. At a constant 60 mph it will take 1 minute. At 30 mph 2 minutes. Your speedometer is allowed 10% error. That should give you some idea of how accurate your speedo is.
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There is a simple and very accurate way of doing this.
There are numbered marker posts every 100 metres on all motorways. One mile is 1610 metres (well actually 1609.344 metres, but 1610 is an error of 0.04% which is insignificant compared to the likely error on your odometer etc.). Therefore 10 miles will be 161 of these posts. Just reset your trip odometer as you pass one of them, note the number on the post, and add 161 on to that number. When you pass the post with that number on, look at you odometer reading. If it is accurate, it will read 10 miles.
If is safest to do this on a motorway that is not to busy and stay in the inside lane, or even better get a passenger to look at the posts for you.
Mike Humpherson.
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This is the method I have used for several cars over the last many years. I have found that Peugeot 205 odometers typically measure 3 to 5 % over (thus apparently improving your MPG figures) but 306s only 2% over. It does not follow that speed is also overestimated, but in my experience the discrepancy is about the same.
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Thanks to all.
I'll probably try the M'way post method.
Incidentally, the diff between 14" 175X70% & 15" 195x60 is less than 2%, so that's not the reason for under-reading!
Roger
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Why not get a friend to follow you in their car over a set course and compare the readings?
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Two wrongs don't make a wright !!
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I realise it might not be the best option but do you fancy being on a motorway full of people concentrating on marker posts instead of the road ahead?
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Richard,
Quite agree, but as I think someone else said earlier in the thread, if using marker posts you should enlist the passenger as observer. My personal suggestion was distance between Service Areas, which is failry easy fro the driver to spot / reset the trip.
regards, Adam
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