Is there any visible difference between 55 and 60?
If I am honest I think a lot of tyre places don't really have a clue how the numbers relate to the size of the tyre.Had the same problem with my old Astra that had 175/65R14 as standard (pretty tiny for a 16v GTE with 155bhp). A couple of places were unhappy fitting 185/60's even though the change in rolling radius was very small.