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Old 08-19-2011, 07:04 AM   #1
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Why do I need "ST" tires?

On our boat trailer there were 3 Goodyear Marathon tires and one Chinese replacement when we bought the previous owned boat. The "China bomb" is falling apart, the Goodyears are OK. I assume the PO had a blowout or something and replaced just the one with a cheap-o.

So they are ST205/75R14 and very expensive for a trailer I take about 500' from the driveway to launch and 2 miles on occasion to go to a gas station. Why would a passenger car tire not work? The boat and trailer doesn't weigh much more than my SUV and passenger tires are fine for it.

BTW I have no problem getting a couple of the Goodyears but if something that is safe will work for less why not?

Mark & Nancy
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Old 08-19-2011, 07:46 AM   #2
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As long as the new tires are rated for the weight I don't see why they wouldn't work just fine.


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Old 08-19-2011, 09:53 AM   #3
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Trailer tires are generally rated to carry more weight than the same size car tire. They also have stiffer sidewalls so the trailer follows better. I had 4 goodyear LT tires on my 10,000 lb trailer for several years (the trailer itself weighs 2,100 lbs). They seemed to do the job, but the trailer seemed to bounce along rather noisily. Last year I replaced them with trailer tires. It follows better and is quieter than with the light truck tires. The trailer tires were a little less expensive than the automobile tires that could carry the same weight. After experiencing the difference I would never go back to a car or light truck tire.

As a side note be sure the tires you buy are physically the same size as the ones you intend to keep. I've had different manufacturers tires with the same size printed on the sidewall that weren't even a close match. In one instance one brand of tires were almost 1" taller than another brand even though they had the same sizes moulded into the sidewall
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Old 08-19-2011, 12:39 PM   #4
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The manual for my 5th wheel said either STs or LTs are acceptable. As noted above, the STs normally have a higher capacity, but, in my experience they do not hold up nearly as well as LTs. Don't know about "P" tires.
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Old 08-19-2011, 12:43 PM   #5
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St trailer tires have stiffer walls if you don't load to capacity you will be ok. I just purchased 2 for my utility trailer $85.00 each not taking a chance on $50.00 difference.
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Old 08-21-2011, 12:00 AM   #6
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HD4Mark......I had a 4500 pound SeaRay with tandem axles that I had for 18 years. We trailered it several thousand miles a year. When the boat was new, I replaced the trailer tires with steel belted radials. The radials really made it ride better and tracked well. I never had an issue.

The ST trailer tires are a different compound that are made to last for years.
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Old 08-21-2011, 07:16 AM   #7
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The tire people recommend against using "P" tires on trailers because of the greater flex in the sidewalls. The stiffer sidewalls of ST and LT tires reduce the tendency of the trailer to roll and sway. But I think in your situation a P-type tire would be fine as long as it has a sufficient load rating (Load Range or Load Index).

I would be a bit concerned about putting a P tire on one of an axle and a ST on the other end, though. That could lead to some interesting sideways movements on the highway. You really want both tires on an axle to be the same type and size.
Gary Brinck
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Old 08-26-2011, 03:43 AM   #8
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The Tire & Rubber Association recommends derating by 10% or so the carrying capacity of P-rated tires when used for trailers. That said, I used P-rated tires very successfully with an old Airstream for many years, but the tires I used had some 25% reserve margin.

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