Trailer tires

Hello Doug Hoffman, you wrote at 01.20.2009 23:59

Jim Beckman wrote:
At 15:14 20 January 2009, flying_monkey wrote:
Gang,

It does not appear that the trailer has any suspension,
so I think I'd run the tires slightly soft, maybe 25-30 psi.

Hard to imagine a trailer without any kind of suspension. Seems to me it
would bounce like crazy over any kind of rough road, not to mention
beating the glider to pieces.

Agreed. An axle using torsion arms for sprung suspension may "look"
like it has no springs, i.e. no leaf springs or coil springs, when in
fact it does.

NACK.

Our club owns self-built (in late 60s and early 70s) trailers for our
K-6, K-8, and K-13 without any suspension except the air in the tires.
None of them is bouncing "like crazy over any kind of rough road", and
none of our planes was "beat to pieces" as well.

However, it's strongly recommendend to drive rough roads more slowly
than with a Suspension.

regards
Werner

Werner Schmidt wrote:

NACK.

Our club owns self-built (in late 60s and early 70s) trailers for our
K-6, K-8, and K-13 without any suspension except the air in the tires.
None of them is bouncing "like crazy over any kind of rough road", and
none of our planes was "beat to pieces" as well.

Interesting. But that would be a deal breaker for me when looking to
purchase a used glider.

Regards,

-Doug

Eric,

Thanks for the input. I've seen your helpful and enlightening posts
on many subjects in this forum, so I'm certainly paying attention to
your advice. My comments are inline below.

On Jan 21, 12:34*am, Eric Greenwell wrote:
I'm leaving this Friday to pick up a glider that I purchased 1100
miles away. *The trailer looks brand new, but is about 12 years old,
as are its tires. *The glider and trailer weigh in the vicinity of 950
#.

What is in it? It is worth weighing it if you are at all suspicious
about the claimed weight.

What's in it is a Russia AC4C, which weighs 330#. I've seen several
pictures, and am not suspicious of the weight. The owner who I've
talked to on the phone had no doubt of the weight, so I'm assuming he
weighed it at some point.


Assuming the 950 pounds is right... Unless you are towing this with a
Volkswagen Beetle, it seems unlikely such a light trailer will cause any
problems, regardless of the tires.

*The tire spec from the owner is :
Carlisle Sure Trail ST
ST205/75014 (replaces F78-14ST)
Max Load 1760 lbs @ 50 PSI *(actual load will be under 500 lbs)

The ST inflation chart show a load rating of 850 pounds at 15 psi! This
tire is serious overkill for the weight of your trailer. Even the
smaller ST175/R13 has a 670 pound rating at 15 psi.

If it were my trailer, I'd just put on passenger car tires with a speed
rating about 20 mph higher than I planned to tow, and a 1000 or so pound
load rating, then use the correct pressure for a 600-700 pound load.


From my experience towing things, some of which is a glider, that's
about where I was thinking of going. I have to buy the tires tonight,
and unless I see some serious refutation of this idea here today,
that's what I'll do. As far as the tire size, I'll probably try to
get around the same rolling radius, as we've already bought a drop
hitch to set the trailer level with the original tires. I'm sure I
can have the dealer look up the recommended inflation pressure for
that load.

I've only seen some pictures of the trailer, and I was inferring that
it had no suspension because there is probably only about 1-2" of
fender clearance, and in the picture, I can't see that the fenders are
free to move with the tires.

Ed

On Jan 20, 4:30*pm, Dave Doe wrote:

If I were you I'd use LT tires (light truck), and run 'em at their rated
60psi (60-65 is about normal for LT tires (should be written on them,
often is)).

The LTX tires on my van has a max pressure of 35 psi so be careful
what you select.

I ran radials at 35 psi on my Minden trailer and it was far better on
rough roads and uneven freeway pavement than my new Cobra which has
smaller wheels and higher pressure tires. I sometimes think getting
the heavy duty suspension was a mistake. It seems too stiff for the
trailer weight.

Andy

At 12:26 21 January 2009, flying_monkey wrote:

I've only seen some pictures of the trailer, and I was inferring that
it had no suspension because there is probably only about 1-2" of
fender clearance, and in the picture, I can't see that the fenders are
free to move with the tires.

It seems unlikely, but still possible, that the trailer suspension
has collapsed. More likely with one of those internal torsion
setups - guys at the field have had trouble with fixing those.
You might want to make sure what the situation is, because
the fix could be expensive.

Jim Beckman

Eric has a point - this is an unusually low weight glider/trailer
combination, and thus warrants a different approach.

For the more typical glider trailer with 15m glider, though, I stick
by my suggestion to use ST radials, as they have sidewalls
specifically designed with trailers in mind. Their sidewalls are
stiffer than a passenger (P) or light truck (LT) tire, are more
flexible when cornering and backing, and are designed for extended,
non-stop towing. Note that LT tires are also designed to carry higher
loads than ST tires, so they're going in the wrong direction for a
glider trailer.

-John

On Jan 21, 12:34 am, Eric Greenwell wrote:

Assuming the 950 pounds is right... Unless you are towing this with a
Volkswagen Beetle, it seems unlikely such a light trailer will cause any
problems, regardless of the tires.

The ST inflation chart show a load rating of 850 pounds at 15 psi! This
tire is serious overkill for the weight of your trailer. Even the
smaller ST175/R13 has a 670 pound rating at 15 psi.

If it were my trailer, I'd just put on passenger car tires with a speed
rating about 20 mph higher than I planned to tow, and a 1000 or so pound
load rating, then use the correct pressure for a 600-700 pound load.

Andy wrote:
On Jan 20, 4:30 pm, Dave Doe wrote:

If I were you I'd use LT tires (light truck), and run 'em at their rated
60psi (60-65 is about normal for LT tires (should be written on them,
often is)).

The LTX tires on my van has a max pressure of 35 psi so be careful
what you select.

LTX is a Michelin designation, and does not mean it's an "LT" (Light
Truck) tire; e.g. Michelin makes passenger car tires in the LTX series.

So, it's a good warning: make sure you are not confusing the name of the
tire with it's type. The type will be in letters at the beginning of the
tire designation: P = passenger, LT = light truck, ST = special trailer.
For example, Michelin Pilot LTX P275/65R-18 114H RBL is a passenger car
tire.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* Updated! "Transponders in Sailplanes" http://tinyurl.com/y739x4
* New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

Hi Gang
There is another important consideration that has not been
thoroughly dealt with in this thread and that is trailer sway with
depends critically on the tires used and their pressures. What is
trailer sway? Well you are tootling down the highway at 50mph and
everything is great and then as you go through 65mph your trailer
begins to swing from side to side much to the consternation of anyone
following you. The only way to reduce this low frequency oscillation
is to slow down fast before the situation can get away from you. So
what are the factors affecting sway? Well the weight of the trailer is
one, the weight of the vehicle hauling, where the trailer wheels are
placed (front, middle or rear) but probably the most critical factor
is the lateral flex of the sidewalls of the tires, wand of course, the
pressure of the tires. When I received my Cobra trailer from Germany
the tire pressures were low about 25psi and what I described above is
a true story. So I pumped the tires up to 40psi and no sway to 70mph
when towing with a heavy vehicle.
In researching trailer sway more fully I found the general consensus
was to use tires with very stiff side walls such as 10 ply non radial
tires (truck tires) and to keep tire pressures up close to the
manufacturers maximum pressures especially if you are going to tow
with a small vehicle. I hope this is of some help.
Dave

Eric Greenwell wrote:
jcarlyle wrote:

Whatever you choose, make SURE that it is an ST tire - this stands
for Special Trailer. And DO NOT run them at low pressure - run them
at whatever the pressure is that is stamped on the sidewall to get
maximum load carrying ability with minimum heat build up.

Be aware ST tires have a 60 mph speed rating at the standard
pressures. You can raise the rating to 70 mph if you inflate to
required pressure for this higher speed.

I didn't remember this correctly: According to a Goodyear general
information sheet:

Based on industry standards, if tires with the ST designation are
used at speeds between 66 and 75 mph, it is necessary to increase the
cold inflation pressures by 10 psi above the recommended pressure for
the load.
o Do not exceed the maximum pressure for the wheel.
o If the maximum pressure for the wheel prohibits the increase of air
pressure, then the maximum speed must be restricted to 65 mph.
o The cold inflation pressure must not exceed 10 psi beyond the inflation
specified for the maximum load of the tire.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* Updated! "Transponders in Sailplanes" http://tinyurl.com/y739x4
* New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

jcarlyle wrote:
Eric has a point - this is an unusually low weight glider/trailer
combination, and thus warrants a different approach.

For the more typical glider trailer with 15m glider, though, I stick
by my suggestion to use ST radials, as they have sidewalls
specifically designed with trailers in mind. Their sidewalls are
stiffer than a passenger (P) or light truck (LT) tire,

According to this page on the Subaru.com website about trailer tires,
the ST is in between the passenger (P) or light truck (LT) tire in
sidewall stiffness.

http://tinyurl.com/9jesg

They also mention ST tires better withstand storage and deterioration
from the elements,including sunlight and ozone, due to the rubber
formulations.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* Updated! "Transponders in Sailplanes" http://tinyurl.com/y739x4
* New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org