There are a few catch 22 problems with speed ratings for ST tires.
1. There is no speed letter for 65 MPH. For many years it’s been well published that ST tires without a speed rating on their sidewalls are limited to 65 MPH.
2. The USA has told many of the China manufacturing plants to include speed letters on their ST tires or pay higher tariff fees.
3. ( A service description identifies the tire's load index and speed rating). Herein lies the biggest of the catch 22s. Service descriptions are not official for ST & LT tires. They were allowed to be displayed on the ST & LT tires in the hope they would become a single description for all tires. It has not happened and the Load Range (Ply Rating) still remains official for the ST & LT tires.
The China plants in all their wisdom have included the speed letter at the end of a service description for their ST tires. Is it valid? I don’t know. From a knowledgeable source I’ve been told that the TRA is still holding firm on the design features of the ST tires being limited to 65 MPH.
I don’t know if I would trust the China speed letters without NHTSA getting involved and confirming the letters to be valid.
Reference:
http://kenjonestiresblog.com/blog/st...ailing-duties/