Tires: Tires, psi max, inflation pressure

Question
What is the standard and Xtra load rating on a 205-50-17 tire.
If a tire manufacturer has a 51 psi max on the tire why does Xl vs. Sl matter?
Thanks


Answer
Jurt,

There are at least three answers to your first question - It all depends on which standardizing body the tire manufacturer is following.  There are 3 major ones - Tire and Rim Association (US), European Tyre and Rim Technical Organization (Europe), and the Japanese Automobile Tire Manufacturers Association (Japan).  The net result is all about the same, but they don't quite agree.

But I sense that your real question is:  Why do I need an XL tire?

Because the vehicle manufacturer determined - mostly through experience - that he needs one to make the car be dependable, handle, etc. - and I should tell you this experience sometimes comes at a high price, so I wouldn't discard it.

Plus, you seem to be suffering under a misconception.

The load a tire can carry is indeed related to the inflation pressure.  For example ALL standard load tires achieve their maximum load carrying at either 35 or 36 psi.  However, it is permissible - sometimes advised - to use higher pressures, so the standardizing organizations allow the use of 44 or 51 psi (no others).

However, an Extra Load tire achieves its maximum load carrying capacity at 41 psi - and the construction of an XL tire is a little stronger to accommodate both the pressure and the load.

So you can not go strictly by the inflation pressure written on the sidewall.