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Originally posted by EXCALIBUR
asn,

34 psi is optimal.:4:

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FYI

There are several tire standardizing bodies throughout the world. In the US it's the Tire and Rim Association. (TRA). In Europe, it is the European Tire and Rim Technical Organization (ETRTO). These people set the standards for dimensions and more importantly, the load tables - that is the load carrying capacity vs inflation pressure. In the case of TRA, the load table generally stops at 35 psi, while for ETRTO the load table stops at 36 psi. For practical purposes these are the same. (please note there are a few exceptions)

Both TRA and ETRTO have approved the use of higher inflation pressures for specific service conditions. One of these conditions is higher sustained speeds.

BTW, these standards apply regardless of who manufactures the tire. Also all these pressures are stated as cold pressures. Heat generation will increase the actual operating pressures, and these must be compensated for in the tire design.

Every vehicle sold in the US will have a placard that will state the OEM tire size and the appropriate inflation for that size tire.

The question is - What happens when you use a higher than placard inflation pressure? The steering response time quickens, the ride deteriorates, the tire wear will be more prevalent in the center of the tread, the impact resistance of the tire goes down, a smaller footprint (meaning wet and dry braking reduction), etc.

Since the discussion hasn't been about the use of 38 to 40 psi, but about 45 and higher, let me offer the following thoughts.

On static burst tests, passenger tires will exceed 100 psi. This does not mean that tires should be operated at these pressures.

Vehicle suspensions are designed to absorb a certain amount of impact energy, the tire absorption rate being factored into the design. As the tire pressure goes up, the vehicle spring rate should be lowered as well as the shock damping should be reduced, to allow the suspension to absorb what the tire used to absorb. Without these changes, the risk of a tire impact failure goes up dramatically.

The use of pressures significantly over the placard elevates the risk of quite a few things - longer stopping distances, increased risk of tip over, decreased resistance to tire failure due to impact, etc.

All these things add up to good reasons not to use pressures at this level.

Hope this helps.

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Originally posted by deltajetfixer
I run the maximum cold inflation pressure on the tire sidewall.

I stopped going strictly by the vehicle placard back in high school. Had a 1971 VW Squareback that specified 18 psi for the front tires...never went there as they just "looked" wrong.

So far, so good. :2:

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