Wheel Sizes vs Actual Miles Traveled?

[Pauls898]

When I purchased my new Audi A4 QSE it had the standard wheels changed from what would have been the 5 spoke 18 inch rims to 11 spoke 17inch rims?

Now my question is because it has now "Smaller" wheels, could this explain the fact that I have been noticing a 10% increase in the actual distance travelled in the car.

For example a standard jouney from my home to my brothers in my old car was always 101 miles? The sat nav/auto route says 105, in my Audi it clocks up 111???

When the dealer changed the wheels for a different size of wheel, should he have changed a setting in the "cars" computer to reflect this change if there is such a setting?

Or is this just a tolerence error between different car manufactures, but we are talking here of about 10% over, and as my car is on a PCP, after 4 years of motoring @ 15,000 per year, were taking here of 1500 miles over @ 12p per miles = £720.00 bill :-( :confused:

[zollaf]

it depends what tyre size is on it, and was on it. you need both sizes, and the google tyre calculator. put the sizes in and you can get the rolling circumference. but if the new ones are actually smaller, then yes, they have to turn more times than bigger tyres over the same distance so would account for the discrepancy.

[Pauls898]

Thanks

I just found this niffty tyre calculator

http://www.miata.net/garage/tirecalc.html

Using the standard Tyre size of 245 40 R18 and my new size of 245 45 R17

It gives me 0.1% ie when speedo shows 60MPH I'm doing 59.9MPH

Hardly anything to worry about here then lol, well it was a thought....?