My wife had a blow-out on Thursday afternoon on our Nissan Maxima, ruined the tire. In our town there are basically 3 main places to buy tires, Wal Mart, Firestone and National Tire. I went to Wal Mart thinking I just wanted 4 round tires, no certain brand. 225/55 ZR 17 size. They said they have to put that exact tire on the car and it is an odd size, because of the Z rating. The Z is a 180 MPH tire and is special order. I called Firestone and they said the same thing. National finally said they would put a W rated tire (150 MPH) on the car and they had them in stock. Why in the hell do they say you have to have a dang 180 MPH tire?

Good question, I'm guessing an attorney had something to do with it.

Sell the customer what they want. Have them sign a disclaimer and do what the customer asked.

Insurance and corporate regulations. That is all.

Tire Speed Rating

this. Had the same issue on a car I had. I put a set of tires with a lower rating on. Drove like crap. Went back to the factory tires.

The suspension on the vehicle is tuned to the speed rating so to speak. The z rated tires sidewall is much stiffer than say an h rated tire. The rubber compound is different as well. You won't feel much difference between a Z and a W rated tire in everyday driving but, its not the correct application. Insurance companies are starting to look at tires when there are accidents. Going down in rating can have adverse effects on stopping distance. Lawyers have had to get involved because the experts "Tire Shops" have let the consumer tell them what's best, and install lesser rated tires to save the consumer $'s and ultimately save the sale. The contact patch on a tire is very small. The slightest variance away from recommended application can make quite a difference on today's vehicles.

Tires is one thing but no one can balance a tire these days. I've bought almost 4 thousand dollars worth of tires in the last week and none have been balanced worth a toot. Dump truck tires, work truck tires and my wife had to put a set on her traverse. Her traverse shook so bad she took it back to the dealer and they gave her a loner for the weekend. They put some kind of bead balance in the dump truck tires( all six ) because they were replaced in the field. Guy said they would be ok but I had to take it by there shop and have the weights put on. It rides much better now. My work truck has a shimmy but I haven't the time right now to go by. TIRES AREN'T CHEAP EITHER!

Insurrance reasons

A combination of several things in previous post. The number one factor is handling characteristics of tire. The car is designed to handle certain ways and require certain tires to do so. The lower the speed rating the harder it handles. The car won't corner , ride or grab like the car you bought and that includes stopping distance . Most tire manufacturers won't warranty a wrong fitment on a car. The car manufacturer ask for a certain spec and that's what needs to go back on it.