I am going to put some all-seasons on my Z..so I decided on the ContiExtremeContact UHP All seasons (255/40-18 and 235/40-18 for a 2.4% offset which is about as close as I could do without new rims to the stock 3.0%)...anyway, I got the price off of Tire Rack and then called my dealer, and he said he couldn't match (however I knew that my dealer gets their tires from tire rack) anyway, I printed out the prices from tire rack and added shipping and the 10 dollar (9 with the Z card) installed and balance..and took it to him...well it came to 694 for me to do it...he saw that I knew exactly what I was doing..and said hell, I can save you 60 bucks and said they would do it for 630 installed....

I guess the moral of the story is know exactly what you want, know the price and your dealer should beat it.