Calculated vs MID off by exact amount the Speedo under-reads? - Insight Central: Honda Insight Forum
 
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Old 01-31-2013, 04:56 AM   #1 (permalink)
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Default Calculated vs MID off by exact amount the Speedo under-reads?

Just a thought. At 70 mph on the speedometer my sat-nav says I'm actually doing 67 mph. My I2 is a UK spec ES with 185/55 r16 tyres.

Meanwhile the discrepancy between my lifetime mpg on the MID and calculated at the pump is about 4-5%. This is also the case for most of my individual fill-ups.

If the odometer has the same error margin as the speedometer, that actually means that the MID mpg is bang-on accurate, if the difference between distance actually travelled and measured by the odometer is taken into account.

Honda must have been aware of the Speedo under-read on the standard tyres. If the odometer is the same, perhaps they used a correction factor for fuel economy ?

What about other people? Is there any evidence that our odometers are under-reading?

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Old 01-31-2013, 07:17 AM   #2 (permalink)
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Default tire size and distance/mpg metrics

If you have 16-inch tires, that's different from the standard on my 2013 Insight. Mine has 15-inch tires; unless we have different programming setups, one of us is getting skewed mph and mpg figures for sure.
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Old 01-31-2013, 07:39 AM   #3 (permalink)
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Not necessarily. Nothing to stop Honda calibrating a trip computer for individual models or locations.

However, it's entirely possible to have very similar wheel circumference for 15 and 16 inch wheels. In the UK we have at least two different wheel sizes depending on model.

The SE and HE models have 175/65 r15. The ES, HS and EX models have 185/55r16. According to this calculator (Tyre Calculator | Tyre Size Calculator difference in wheel circumference is 6mm or less than 0.3%.

Narrower tyres generally give slightly better mpg and this is reflected in the official mpg ratings for the different models. The weight will have some effect too.

The MID has some differences between UK, mainland Europe and US cars - don't see why speedometer or oedometer calibration shouldn't be among them. There will be local regulations regarding the accuracy required for the speedometer and odometer in different areas.

Having said that, I would have thought that Honda would be cautious about inaccurate oedometers by now. There was a 2007 class action brought by Accord owners, who ended up getting a small amount of compensation and the mileage for their warranties extending slightly.
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