Since you haven't bothered to tell us what type of car, year, etc, and your profile doesn't list what type of Ferrari you have: The 25mm Hill Engineering spacers for the rear wheels makes a world of difference on the 89-92 348 ts and tb models. 93 and up already have the 50mm wider rear track, as does the 355, so no spacers required - it's good as is.
The previous owner of my F355 installed front and rear wheel spacers. The front fenders were rolled to allow the tires to align with fenders. The car looked awesome, but it wasn't too stable when doing the twisties and the back had a tendency to break loose on agreesive turns. I also had to check/retighten the lug nuts after each performance drive. After removing the spacers, the car handles much better and feels more stable. If you really want the spacers, I can sell it to you cheap.
sorry. my bad. I guess nobody could read my mind. Difficult to ask for tire and spacer advise when I don't tell you my details: 348 TS 1993 Tire size: 215/50ZR17 and 255/45ZR17
Just a note: the oversteer/understeer of the 348/F355 can be completely controlled with rear ride height (while front ride height can be used to control bump steer.) Adding width to a (relatiely) short wheelbase car makes the car react faster to steering inputs, whether desired or not; and detracts from high speed stability.
