At what psi can I travel 65-75mph?

Francesca Knowles wrote:

JJBIRISH wrote:


I don’t agree with your assertion that the ST tire is a passenger tire… the ST is not designated as a passenger tire

I didn't assert it was a "passenger tire", a phrase I take to mean a P-metric.

If I may paraphrase: I said that since there are many States that allow for passenger transport in trailers equipped with ST's, the oft-repeated argument that they're "not as safe" as P's/LT's etc. doesn't hold water.

I continue to maintain that every tire approved for highway use must meet the same standards of SAFETY- this due at least in part to the obvious truth that "unsafe" tires pose as great a risk to bystanders as to the operators of whatever it is that's on the road.

Well you exact quote was…

“No matter how many times it gets repeated in forums like this one, it is NOT a "fact" that ST tires are "not intended to carry passengers".”

Because some states allow a passenger doesn’t in fact make a ST tire a passenger tire… they are not…

they are a special purpose tire for trailer use only… passenger is generally referred to as P metric but the LT tire is also considered as a passenger tire, that can be used on SUV’s without having to be de-rated first like the P metric would…

Believe what you will, the ST tire DOES NOT MEET THE SAME testing and safety requirements as the other highway tires do… and IMHO they are not as safe as P or LT tires…

They (the ST) and temporary spares and bias ply tires and my lawn mower tires are not required to meet the same and much more stringent safety requirements of a P rated or LT tire…

§571.139 Standard No. 139; New pneumatic radial tires for light vehicles. S1. Scope and purpose. This standard specifies tire dimensions, test requirements, labeling requirements, and defines tire load ratings. S2 Application. This standard applies to new pneumatic radial tires for use on motor vehicles (other than motorcycles and low speed vehicles) that have a gross vehicle weight rating (GVWR) of 10,000 pounds or less and that were manufactured after 1975. This standard does not apply to special tires (ST) for trailers in highway service, tires for use on farm implements (FI) in agricultural service with intermittent highway use, tires with rim diameters of 8 inches and below, or T-type temporary use spare tires with radial construction..

You can see the types of tires segregated out of the standard, and you just have to ask why the ST tire… I mean I can see farm tires being left out, but come on… the only radials not included are the temporary spare and the ST…


ST tires are regulated under Standard No. 109 that wouldn’t hold a candle to 139 as a safety standard and even at that 139 is watered down because of industry lobbying but was needed because of the long overdue and out dated 109 standard…