My '07 Civic Si Sedan door panel sticker says my car needs tires with a load rating of 91. It's the only load index number on the car.

The manuals list 87 as the standard tire/load index and 91 as an optional summer tire.

The issue is that tire stores will not put a tire with a lower load index on the car, if they do they will not warranty them and they say it will violate the manufacturers warranty as well.

This is a problem as there are few tires with a 91 rating, almost none with mileage warranties and they are all expensive - and do not last very long.

Does anyone know if the Si require a 91 tire or it's optional - and do you have a reference for that.