The stock wheel size is 17". Nothing smaller will fit over the stock brakes on a Ram. I'd tried once to mount 16" rims from my jeep on my truck cause I was curious about how the rims and tires would look, but they would not clear the brakes. Hope that helps.

I dont want to hurt your feelings but I am going to bet it won't work very well at all. I think you are going to have to find a bigger master cylinder because I'd be willing to bet the piston is larger on the Ram caliper than the Audi caliper.