OP needs a different tire shop. 275/60 18 fits. No rubbing, no issues. Everything is fine. Smaller diameter or less width will fit without problems, too - that's fact.

Tire shops can be unwilling to sell or install something that deviates from manufacturer specs. If they do it and you don't like it, you'll be back wanting them to take back the tires and redo the install for free. The rework and return, sticking them with four tires that aren't new any more, costs them more money than your work is worth. So they tell you it won't work to save them themselves the potential problem.

What's needed is an indy that will do what you want and won't give you crap. Look for locals, and think about ordering from TireRack and using one of their installers, with a call beforehand to talk about what you want them to do. I've been successful doing that. I've also sometimes used a local mechanic that's done work on my cars for many years.

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