Originally Posted by Wobbles
Do you have something definitive about a standard change that is coming?
You had my hopes up...
Standards are not changing. The standards simply indicate a tire's dimensions and the load and inflation they are to carry when being tested against the federal DOT regulations as covered in "49 CFR Part 571, Subpart B - Federal Motor Vehicle Safety Standards"
The speed rating symbol seen on tires is not part of this DOT. Speed ratings come from a different set of tests established by Society of Automotive Engineers (SAE).
To make matters more complex it is the Commerce Dept that is invoking tariffs on certain tires from Asia, with certain exceptions that involve different "types" of tires (P or LT or ST). As I understand it early on in the hearing and negotiation phase the subject of speed ratings came up as a method of identifying certain tires that would gain an exemption from the tariffs. It appears that the increase costs of improving the speed capability of some tires was less than the proposed tariff.
So what is changing is the design spec or objectives of tires being made for import to the USA. Some tires that in the past were not designed to be able to meet SAE testing will in the future be able to meet the existing SAE standards but 571.110 — Tire selection and rims and motor home/recreation vehicle trailer load carrying capacity information for motor vehicles with a GVWR of 4,536 kilograms (10,000 pounds) or less.
571.109 — Standard No. 109; New pneumatic and certain specialty tires.
571.119 — Standard No. 119; New pneumatic tires for motor vehicles with a GVWR of more than 4,536 kilograms (10,000 pounds) and motorcycles.
571.139 — Standard No. 139; New pneumatic radial tires for light vehicles.
are not changing any time soon to the best of my knowledge.
Be forewarned reading and trying to understand the legal and techno babble in the above regulations can give you a headache
RE the tire size change question. Tire OD and width is limited by clearance between the tires and the frame & bodywork and tire to tire clearance in multi axle application. I do not understand the issue of axle strength and tire OD as the bending force of the axle spindle is not affected by tire OD but by wheel offset and the amount of force (load) on the tire.
Comment on tire size. When identifying a tire size it is critical to include the letter prefix or lack thereof as a ST205/75R14 LR-C is not the same thing as a 204/75R14C as the second size is a "commercial" size tire based on European standards and has a different load capacity as the ST type tire that is based on US standards.