Odometer (in)accuracy

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So we all know the speed over reads by around 5%, but I now realise the odometer does too. Example, I regularly do a run which is 100 miles according to my other cars, yet the same drive in my McLaren is 106 miles. I'm coming up to 20,000 miles on the clock, but it is really only 19,000! Annoying.

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HIS LM said:

How do you know your other cars are not under reading ?

My Lexus registers 100 miles for the same trip, which is the same distance as Google Maps thinks it is.

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CarCrazyDad said:

targarama said:

So we all know the speed over reads by around 5%, but I now realise the odometer does too. Example, I regularly do a run which is 100 miles according to my other cars, yet the same drive in my McLaren is 106 miles. I'm coming up to 20,000 miles on the clock, but it is really only 19,000! Annoying.

From my understanding on most cars
The true mileage is recorded and is what is displayed on the ODO

The natural speedo over reading is not what contributes to the odometer total - the car knows exactly how many miles it's done (well, much more precisely than the speedo would imply)

Seems odd that the trip would add a different amount to the odo though. Why would the trip not be accurate? Of course I agree the speedo over reads, and accept that.

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CarCrazyDad said:

It doesn't though

Let's say you're doing an indicated 74mph
This may be (for arguments sake) a true 70mph.

If you drive for an hour then you will have 70mi displayed both on your Odometer and your trip computer (not specific to Mclaren but any modern car).

But the trip is showing 74 miles. Not 70. That is my point. This image below is for a 100 mile journey according to Google and my Lexus:

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I just read a post on the McLaren Life forum thread referenced above where someone changed tyres to wider tyre with a slightly higher overall circumference reducing the speedo/odo difference from 4% to 2% (their measurements). They suggest the 570 is not calibrated specifically for this model, but instead keeps the 650 calibration settings.

Anyway, I'm not too fussed as long as every McLaren 570 is over registering on it's odometer