Paul Giverin wrote in message
...
In message ,
Paul writes
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 lower the aspect ratio of the tyres then there will be
minimal change to the rolling radius. If you don't change the
aspect ratio then there will be negative effects of gearing and
speedo reading.

More info he- http://www.carbibles.com/tyre_bible.html

Cheers Paul, particularly for the link.