Originally Posted by A W Warn
A hypothetical question:
Assume two tires are of the same size, one D rated the other is E rated. Both are inflated to exactly the same pressure, that is below the maximum inflation for either.
Does one of tires have the ability to carry more or less load when at the equal inflation pressure?
I think I know the answer, but do not recall that I ever heard this question asked or answered before.
Well Capri got to the computer first so I guess he wins.
It might help to understand that answer if you think of a tire for what it really is. Just a container of pressurized gas. It is the pressurized gas that supports the load.
Many time people do not understand what physical differences there may be in tires that appear to be the same except for their Load Range.
There are a number of tests tires must pass and the conditions of the tests are based on the Max load capacity at the appropriate pressure for that load.
These tests include the ability to stay seated on the wheel and another may measure a tire's ability to resist a tread puncture of a special 3/4" dia steel rod.
Sp lets assume we run a tire company and have a LR-D tire already in production and want to add a LR-E. We do the testing and discover our prototype which is based on the LR-D construction passes all the tests except maybe the tread puncture test. So the best thing for us to do in that case would be to increase the strength of the belts.
If however our prototype passed all the tests except the bead test we would need to change the strength of the bead wire. The bead is the band of wire that retains the tire on the wheel.
So depending of test data a tire company will modify prototype constructions to provide the strength required to deliver satisfactory performance. These changes may be minor in some cases and major in others with no way to predict the changes or see them by simply looking at a tire.
Note the above are just two of the dozens of tests a tire must pass but I limited the number to make the answer easier to understand.