My thoughts on the ST tire debate previously shared on another forum:
Few things generate more passion than discussion of tires on the forums. Since I was not a tire expert I did a lot of research before making my decision on tires. This includes researching every related forum I could find and corresponding with different tire manufactures directly.
The above picture shows my M8008 Maxxis tires at 32,000 miles being replaced with a new set of M8008 tires. My old tires have traveled from Canada to Mexico in snow, mud, gravel and washboard roads without a failure. I saw no defects in my tires when I replaced them, in fact they look almost like the new ones.
At the time I acquired my trailer there were a lot of postings about tire failures on Casitas and other travel trailers.
The US manufacturers had outsourced trailer tires (ST) overseas and there were apparent startup quality problems.
At the same time, Casita
and other trailer manufacturers were equipping their trailers with inadequate load rated tires on their trailers. Casita
was offering ST205/75R-14, 6 ply, 1,760 lbs capacity ea.(or 3,520 total lbs) load range "C" tires, inadequate for loads experienced on the road.
The heavier SD model Casita
trailers when loaded weigh up to 3,500 lbs. (Measurements at the Oregon Ralley)
Casita now offers 15" load range "D" Goodyear tires as an option that seem to be holding up well.
I contacted Maxxis Technical Support and asked them what was the best tire I could put on my 3,400 lb loaded Casita trailer. The response was the Maxxis M8008 ST tires, 225/75R/15. load range "E" tire. These 10 ply tires are rated to carry 2,830 lbs each at 80 psi. Maxxis ST tires are specifically designed for trailers.
Discount Tire has been the largest independent tire distributor since 1960, as such they should have some insight into tires for trailer use, here is what they say.
Why Use An "ST" Tire
*"ST" tires feature materials and construction to meet the higher load requirements and demands of trailering.
* The polyester cords are bigger than they would be for a comparable "P" or "LT" tire.
* The steel cords have a larger diameter and greater tensile strength to meet the additional load requirements.
* "ST" tire rubber compounds contain more chemicals to resist weather and ozone cracking
* Always inflate trailer tires to the maximum inflation indicated on the sidewall. (They say this twice to get your
attention. Anyone that tells you over inflation of trailer tires is the leading cause for failure is WRONG).
* In approximately three years, roughly one-third of the tire's strength is gone. (Another reason why you need a tire
with a load rating that greatly exceeds the weight
of your trailer).
* Three to five years is the projected life of a normal trailer tire.(forget what you know about passenger tires, it does not apply to trailer tires).
* It is suggested that trailer tires be replaced after three to four years of service regardless of tread depth or tire appearance.
Trailer Tire Facts - Discount Tire
According to Mac Demere of 'Edmunds,' nearly every tire blowout occurs on a warm day, on a straight road, at highway speeds when a tire is under-inflated.
Tire Rack says:
"Your trailer is a follower, which often makes tire sidewall flexing a negative. Sidewall flexing on trailers, especially those with a high center of gravity (enclosed/travel trailers) or that carry heavy loads, is a primary cause of trailer sway. Typical passenger radial tires with flexible sidewalls can accentuate trailer sway problems. The stiffer sidewalls and higher operating pressures common with Special Trailer (ST) designated tires help reduce trailer sway.
Goodyear Tire Company says this:
"For trailer tires, inflating near the max pressure indicated on the tire sidewall is a good option for cooler running lower rolling resistance and load-carrying capacity.
If the load the tire is carrying isn't near its capacity, lower-than-maximum psi can be used (see load and inflation tables for proper inflation) and this may give a slightly better ride, but never allow the tires to be under-inflated (lower than what the trailer manufacturer recommends)."
"Industry standards dictate that ST tires are restricted to a speed of 65 mph unless a different speed restriction is indicated on the tire sidewall. If speeds from 66 to 75 mph are used, the tire cold inflation pressure can be increased by 10 psi without any increase in load." (Same thing Maxxis told me, wheel pressure maximum rating must be considered if over inflating the tires to run at higher speed).
I don't ride in my trailer so a "slightly better ride" is not a consideration. I inflate my tires at near maximum, I want the cooler tire temp and maximum load carrying capability. With some 40,000 miles now on M8008 tires without any failures, I am completely satisfied and have zero worries about tire performance as I travel down the road.
Gary RV Forum Staff: Trailer tires seem to be prone to early failures. There are several potential reasons and the anecdotal reports we get are seldom detailed enough to make sound conclusions. Here are some of the major factors:
(1) Most trailers have barely adequate tires right from the factory. By that I mean that they are rated just high enough
for the axle
GAWR, so that they are always running right at their outer limit of capacity. To make matters worse, trailer manufacturers have been skimping on the axle ratings as well, so that the axle itself is usually loaded right to the max in normal use. In my opinion this high level of stress causes trailer tires to fail far more often than passenger car cars, which typically have a substantial safety margin in carrying capacity.
(2) Trailer tires (and RVs tires in general) do not get regular use (exercise). Instead, they sit around getting stiff and flat on one side and the anti-aging chemicals in the rubber do not get spread around. Then they get taken out on the highway and run hard and hot on the highway, usually in hot summer weather. And sometimes on rugged roads too (campground access roads). This is the worst style of usage for a tire, according to tire manufacturers, and leads to a failure rate greater than average for all tires. Some people also feel that long exposure to sun (UV damage) and contact with the ground or concrete will also cause tire damage while it sits. I don't see any meaningful difference vs passengers cars, though, and they routinely last 4-5 years or more.
(3) As with many RVs, trailer tires are often underinflated for the load. Yeah, I know, YOU always check yours and never run under-inflated (and your dog never barks in the campground either), but weight checks by the RVSafety Foundation show that a substantial percentage of RVs have one or more tires under-inflated for the actual load. An under-inflated tire flexes more than it should and gets much hotter than when properly inflated. That greatly increases the likelihood of tread separation or sidewall failure, i.e. a "blow out".
It is my contention that most trailer tire problems are the result of using tires with inadequate load ratings for the trailer weight
along with inadequate inflation to allow the tires to handle the load. Tire age, sun damage, and not moving the trailer for long periods in storage are also contributors to failures.