Tires: Trailer Tire Blow Outs, tire blow outs, inflation pressure

Question
QUESTION: I have a 25" Fourwinns (approx 6,000 lbs).  Bought the trailer new with the boat in 2006.  In 2008 we bought four new tires from Plaza Tire in St. Louis.  On July 5, 2011, we had a blow out - took it to tire place and they could not tell us why (all tread looked new but just fell off tire and then blew).  We had another blow-out on July 17th had another one and they still said nothing was wrong - we had two blow out on the way to the tire place to get them changed.  Is that normal?

ANSWER: Tammy,

Obviously that is not normal, but the question is: what is going on.

So let's start with the tire size and inflation pressure.  There may be letters in front of or behind the numbers in the tire size - and those are important.  Typically, tires for trailers are ST type tires (they start with the letters "ST") and they come in Load Ranges - indicated by a single letter (C, D, or E)

LT type tires are also sometimes used - and they start with the letters "LT" - and they also come in Load Ranges.

So what tire size are these and if there is a Load Range, what is it.  What inflation pressure are you using?  How often is it checked?

Have you ever weighed the rig?  If you haven't, I would suggest you do so - fully loaded, with everything that you can think of that would ever be in the trailer when towing it.

Let's start there and see where it leads.

---------- FOLLOW-UP ----------

QUESTION: Tire size is ST225/75R15 (which is recommended on the trailer) and the pressure recommended for tire is 65 which is checked each time before we pull the trailer.  Not sure the exact weight but we will take it and have it weighed with fuel and water in the holding tank.  I am going to take one tire that blew to a different tire place and have them weigh-in so that maybe this will not happen again.  Is that a good idea since I do not trust Plaza Tire?

Answer
Tammy,

I've heard lots of reports of problems with ST type tires.  I don't know what to attribute it to, but I do know that:

1)  Trailer manufacturers are known to skimp on tire size.  I've seen situations where the tire as supplied on the trailer did not have enough load carrying capacity on the as delivered trailer - let alone when the trailer was loaded up.

2)  Trailer manufacturers are very cost sensitive on tires, so even if they get a large enough tire, they tend to buy from low cost suppliers, so the high cost (and high quality) manufacturers have gotten out of the business.  

Personally, I wouldn't even bother to take the tire to another place.   Unless the tire was blown out because of a puncture and some other road hazard - and that ought to have been pointed out to you when the tire was dismounted - there is hardly anyone who can properly diagnose a tire failure.  The ones that can are either employed by tire manufacturers or will charge a couple thousand dollars.     

But if I were you, I would not postpone getting the trailer weighed.