Paul wrote:
Dave Plowman (News) wrote in message
...
In article ,
Paul wrote:
have a standard Megane diesel with the original 13" steel
wheels
fitted.
have some 14" alloys, will fitting these have any negative
effect
on economy?
what if I went up to 15"?
If you fitted larger wheels and pro rata tyres you'd raise the
gearing.
Generally this results in better economy. But difficult to
check because
the odometer would now give an incorrect reading.

Thanks Dave, you set me thinking. The last time I changed some
wheels on a car, I went from 13" to 15" and it was the first time
since I had owned the car that the speedo reading tallied with my
satnav, previously the car was always showing about 4mph faster.

I've used my Tomtom in several cars and it never agrees with the MPH.
The car always reads 2-3 MPH faster. I'll bet the Tomtom is correct.