Tires: Tire size Change, inflation pressure, winter tires

Question
Barry, I have a 2010 Audi S5.  For the winter I went from the standard size of 255/35 r19 to Blizzaks 245/45/ r17.  The dealer says to stay with the same pressure that is on the placard, but that just doesn't sound right.  Your thoughts?

Scott

Answer
Scott,

Here's the scoop.  Your original tires were Extra Load - 96Y.  But your winter tires are Standard Load - 96 something.  That means you could use 6 psi less than the placard and get the same load carrying capacity.

But there is a school of thought that says that the spring rate - which is pretty much controlled by the inflation pressure - is more important than load carrying capacity, provided there is enough load carrying capacity.

So there you go.