Tendons

Tire rack man thought that most people could not tell the difference in handling or ride between the two sizes.Has anyone had experience with both sizes on a s5 cab?

Barrels41

My A4s:
2009 P+ sports package 18" Pirelli P7s summer tires
2012 A4 S-line 19" Conti 3

Both handled very well and there is no major difference. 19" tires make me nervous on NYC rough roads.

I used winter tires on the OEM 18" wheels but need wheels for the winter 17" or 18". Winter potholes required rim straightening.

The 2012 rides better, Seems to have a bit more ground clearance, better control and firmer seats.

Of course all-seasons give up handling and grip for convenience and low price.

Reggie

Many will not. But many can tell the difference. The big difference will be in the type of tire.

The smaller wheel will tend to be softer and will protect more against pot hole damage. I run 19's on my RS and the Q5 for winter. They work great. But I run 20" for the Q5 for summer. These are the sizes the cars were designed to run. On my 98 A4 I bought 17's to run summer tires on and kept the 16's for snow tires. But I hated the ride and looks so much of the 16s that I finally went 17's for snow tires too.