Let us know if it comes back. My 18" were Michelin tires and smooth as silk at all speeds but I still had the shudder. My shudder is not bad but I feel it. I didn't think much about it until I read on here that other people had it. I only feel it at light throttle because if you get into the peddle heavier it rips past it so fast that you don't notice it.
My 20" are Bridgestones and not Pirelli. The Pirelli is the same size yet it is almost 1" narrower and .1" shorter (how can that be). They look skinny on the wheel compared to the Bridgestone. I shopped until I found a set of wheels with the Bridgestone tires. You can look up the specs of all these tires on Tire Racks website. The specs say the Pirelli is .8" narrower but I swear it looks like more than that in person.