Going from a 45 to 55 series tire?

[Philly215]

I have a 2011 A4 Premium plus with no sports package so it has 17" wheels. I had H&R sport springs on the car but I had to put the stock springs back on because the roads where I live were just destroying the car. The gap is driving me crazy though and it makes the wheels and tires look really tiny compared to the car. I believe the car has 45 series tires on it but not positive, so I was thinking of going to a 55. Is this doable? Will it cause any issues like clearance problems, speedometer, rubbing, etc? I was also thinking of getting 18's with a 45 series tire and that would effectively accomplish the same thing.

[Doc@tirerack]

any tire size that is taller than stock (by more than 5%) will affect ABS and traction control (if available). Trying to decrease the gap between the tire and fender should only be tackled by using a lowering spring. If available, the Eibach ProKit springs will lower the car about an inch and still maintain most of the comfort from the "stock" springs.