like q5

do 255/50/19 give better perf/brak than std 235/55/19 on my q5?

B490MTL

I suggest you try the q5 forum

Doc@tirerack

The slightly wider footprint of the 255 ( about 0.3" wider on average) will help with lateral stability and acceleration / braking, but you can also improve those capabilities by using a more "aggressive" rubber compound in the stock tires size as well. The change in the size of the contact patch is minimal at best, so don't over think things.