RE: [VAL] Back to steel tire stems and the why's and what-for

["David Tidmore" <dtidmore@xxxxxxx>]

As one of the first to start preaching the gospel of steel valve stems about
18 months ago, I whole heartedly agree with Tom (tires, rating, stems). 

On the matter of tires types (P, LT, ST, etc), understand that the tires on
a trailer are exposed to forces unlike a car or truck as they are subjected
to a lot of sideways scrubbing forces (when the trailer turns the tires are
still pointed straight ahead and so they have to twist a bit in place as
they roll during a turn.  ST rated tire sidewalls absorb the twisting forces
so that the tread underneath do not wear excessively and remain in solid
contact with the road.  This means the sidewalls have to be of a completely
different design.  As Tom also pointed out, beware of ply ratings.  Look to
find the ACTUAL tread and sidewall ply numbers (physical, not rated).  

I want to point out about the rubber valve stems can fail without blowing
the entire stem out of the tire.  In my case, after the stem failed,
inspection revealed that the stem had been wearing where it entered the rim
and this eventually caused the stem to no longer seal.  The actual failure
was instant. For the record, at the time of failure, the tires had less than
5000 miles on them.  According to Discount Tire, the failure was the result
of the stem pressure rating being inadequate (ie 65PSI stem on a tire
running 65PSI cold inflation pressure).  This was causing the stem to ride
up and down in the rim causing wear the stem (ie higher pressure was trying
to push the stem out of the rim so the stem was not properly seated).  Now
that I have active tire pressure monitoring, I can see that the trailer tire
pressures rise to about 72PSI at normal highway speeds and conditions, so
the 65PSI stems were an accident waiting to happen. The failed stem remained
in the rim, but the little balls of rubber on the rim all around where it
failed showed friction and heat at work.  In examining the other tire, we
also found the same wear pattern on that stem, so BY ALL MEANS, spend the
money and get rid of those rubber stems, especially if A/S recommends
60-65PSI cold inflation pressure. As Tom pointed out, steel stems are not
expensive and they certainly are good insurance.  

Although everyone knows the mantra, check the tires, check the tires,
Goodyear states that a tire run 10% below the pressure encounters TWICE the
wear, all due to overheating caused by excess flexing of the cords and
rubber.  They also state that running 10% above MAX pressure (measured cold)
is far less detrimental to the tire than 10% below the recommended pressure
for any given loading.  If uncertain as to the proper cold inflation
pressure, go with the max pressure rating for the tire.  You will not damage
the tire although the ride in the trailer may be a bit harsher if the max
inflation pressure is significantly above the amount needed.  It is best to
actually know the loads for each tire on your particular rig and then use
the appropriate pressure (ie take it loaded to a certified truck scale and
have each wheel load individually measured). 
 
David