Cobra Trailer Tires (US)

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On Jul 22, 5:24 am, RN wrote:
The tires on my Cobra trailer from the factory are marked
185R14C8PF (102/100N)LT

They appear to be GT Radial Max Miler X
Load Range D 1875 lb at 450KPA 65# cold

They need to be replaced, and the local tire stores seem to be having
an issue identifying the correct replacement. A brief web search has
also been unsuccessful.

Any advice on the correct replacement, or where to find the code for
reading the markings would be appreciated.

John

I'm using Yokohama 185R-14 steel belted radial light truck tires. The
model is Y356. I drive too fast for ST tires and these have worked
well for 3 years.
Discount tire sells them for about $100/ea.

At 12:24 22 July 2008, RN wrote:
The tires on my Cobra trailer from the factory are marked
185R14C8PF (102/100N)LT

They appear to be GT Radial Max Miler X
Load Range D 1875 lb at 450KPA 65# cold

They need to be replaced, and the local tire stores seem to be having
an issue identifying the correct replacement. A brief web search has
also been unsuccessful.

Any advice on the correct replacement, or where to find the code for
reading the markings would be appreciated.

John


Tyre marking decode...

http://homepage.ntlworld.com/cattermole/tyres.htm

jcarlyle wrote:

Now this assumes that you stick with using ST tires on your trailer.
According to my research, ST rated tires are optimized for load
carrying, and an ST tire of given dimensions will carry more load
while running cooler than an LT or a P rated tire of the same
dimensions. Running cool is the key to tire longevity and preventing
blowouts and tread separation.

Trailer tires (ST designation) don't necessarily run cooler that LT or P
rated tires. Their optimization tends towards longer life (years, not
miles) because they typically aren't used as much or as often as car or
truck tires. They are not optimized for speed, and the load rating has
to be derated over about 65 mph.

My experience with ST tires recently led to me use LT tires instead, but
with a speed rating well above (say, 20 mph) my towing speed. The speed
rating ensures the tread has good lateral stiffness for stable towing
and plenty of margin to avoid tread separation.

--
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, Eric,
Here's a link to a fairly definitive article on trailer tires:
http://www.discounttire.com/dtcs/inf...ionAnxiety.dos
As you can see, it states that trailer tires are indeed optimized for
load, and that for the same dimension an ST tire carries more load
than a P or LT tire.

You're right that ST tires have a speed limit of 65 mph. If you want
to exceed 65 mph, then you do indeed need a different tire rated for a
higher speed. But from the above, you need to select a bigger
dimensioned tire to handle the load properly. I can't find the source
right now, but I read somewhere that you need to derate the load
rating of a P or LT tire by at least 20% if it's on a trailer.

-John

On Jul 23, 2:21 pm, Eric Greenwell wrote:
Trailer tires (ST designation) don't necessarily run cooler that LT or P
rated tires. Their optimization tends towards longer life (years, not
miles) because they typically aren't used as much or as often as car or
truck tires. They are not optimized for speed, and the load rating has
to be derated over about 65 mph.

My experience with ST tires recently led to me use LT tires instead, but
with a speed rating well above (say, 20 mph) my towing speed. The speed
rating ensures the tread has good lateral stiffness for stable towing
and plenty of margin to avoid tread separation.

Eric Greenwell - Washington State, USA

A Yokohama Y356 size 185/R14/D load rated tire inflated to 65psi has a
load rating of 1850lbs which is plenty for a 18 meter glider/trailer.

jcarlyle wrote:
Hi, Eric,
Here's a link to a fairly definitive article on trailer tires:
http://www.discounttire.com/dtcs/inf...ionAnxiety.dos
As you can see, it states that trailer tires are indeed optimized for
load, and that for the same dimension an ST tire carries more load
than a P or LT tire.

Looking at inflation charts for ST and LT tires, they do show the ST
tire having a higher load rating at the same pressure. Consider a
205/75R15 (load range C) tire at 50 psi: ST-1820 lbs; LT-1655 lbs.
Still, it's irrelevant as two LT tires give a 3300 pounds capacity, way
more than needed for all but the very heaviest gliders. Those can use
load range D tires to get a 4000 pound load capacity at 65 psi.


You're right that ST tires have a speed limit of 65 mph. If you want
to exceed 65 mph, then you do indeed need a different tire rated for a
higher speed.

Not neccessarily: the ST tires can be used between 66 and 75 mph, but
they must be run at 10 psi higher pressure IF the tire and wheel are
rated for that (from a Goodyear Marathon ST info sheet - might not apply
to every ST tire).

But from the above, you need to select a bigger
dimensioned tire to handle the load properly. I can't find the source
right now, but I read somewhere that you need to derate the load
rating of a P or LT tire by at least 20% if it's on a trailer.

Note that the LT load ratings from the are for same for trucks and
trailers - no derating like P (passenger) tires require for use on
trucks or trailers. From a Goodyear inflation table title:

"SERVICE LOAD AND INFLATION TABLES [for]
LIGHT TRUCK METRIC TIRES - FOR TRUCKS, BUSSES, TRAILERS AND MULTIPURPOSE
PASSENGER VEHICLES USED IN NORMAL HIGHWAY SERVICE"

Finding a LT tire to fit a glider trailer may be problem. I'm using a
LT185R14 that Michelin doesn't seem to make anymore, and LT 14" tires
aren't common. Goodyear does show an LT195/75R14.

--
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, Eric,

You've got some pretty good arguments there for using LT tires on
trailers. For me they're moot, though - you can't find LT tires to fit
13" wheels (I explained previously why I'm not changing wheel size).

And even though I have a heavy foot when driving, I hold it at 65 mph
maximum when pulling my Cobra. This board is full of too many horror
stories that happened to people pulling trailers, so I decided not to
compound my problems with speed. Thus I don't need a higher speed
rating than ST tires give me.

At least we agree that using P rated tires on a trailer isn't a good
idea!

-John

On Jul 23, 6:14 pm, Eric Greenwell wrote:
jcarlyle wrote:
Hi, Eric,
Here's a link to a fairly definitive article on trailer tires:
http://www.discounttire.com/dtcs/inf...ionAnxiety.dos
As you can see, it states that trailer tires are indeed optimized for
load, and that for the same dimension an ST tire carries more load
than a P or LT tire.

Looking at inflation charts for ST and LT tires, they do show the ST
tire having a higher load rating at the same pressure. Consider a
205/75R15 (load range C) tire at 50 psi: ST-1820 lbs; LT-1655 lbs.
Still, it's irrelevant as two LT tires give a 3300 pounds capacity, way
more than needed for all but the very heaviest gliders. Those can use
load range D tires to get a 4000 pound load capacity at 65 psi.



You're right that ST tires have a speed limit of 65 mph. If you want
to exceed 65 mph, then you do indeed need a different tire rated for a
higher speed.

Not neccessarily: the ST tires can be used between 66 and 75 mph, but
they must be run at 10 psi higher pressure IF the tire and wheel are
rated for that (from a Goodyear Marathon ST info sheet - might not apply
to every ST tire).

But from the above, you need to select a bigger
dimensioned tire to handle the load properly. I can't find the source
right now, but I read somewhere that you need to derate the load
rating of a P or LT tire by at least 20% if it's on a trailer.

Note that the LT load ratings from the are for same for trucks and
trailers - no derating like P (passenger) tires require for use on
trucks or trailers. From a Goodyear inflation table title:

"SERVICE LOAD AND INFLATION TABLES [for]
LIGHT TRUCK METRIC TIRES - FOR TRUCKS, BUSSES, TRAILERS AND MULTIPURPOSE
PASSENGER VEHICLES USED IN NORMAL HIGHWAY SERVICE"

Finding a LT tire to fit a glider trailer may be problem. I'm using a
LT185R14 that Michelin doesn't seem to make anymore, and LT 14" tires
aren't common. Goodyear does show an LT195/75R14.

jcarlyle wrote:
Hi, Eric,

You've got some pretty good arguments there for using LT tires on
trailers. For me they're moot, though - you can't find LT tires to
fit 13" wheels (I explained previously why I'm not changing wheel
size).

There's not much choice in the 14" size I have, either.

And even though I have a heavy foot when driving, I hold it at 65 mph
maximum when pulling my Cobra. This board is full of too many horror
stories that happened to people pulling trailers, so I decided not
to compound my problems with speed. Thus I don't need a higher speed
rating than ST tires give me.

Slower is always more stable towing. You can reduce the tire heating
(and chances of tread separation) by using a higher pressure than
required for the load, as long as the wheel is rated for it.


At least we agree that using P rated tires on a trailer isn't a good
idea!

I think it can be done safely in some cases. For example, choosing a
tire with plenty of load margin (say, more than 20%) and running it at
the maximum rated pressure, and towing at 60-65 mph.

Going to a larger rim diameter and lower aspect ratio tire (to maintain
the same outside diameter) with a high speed rating has also been
successful. The lower aspect ratio improves the stability and the high
speed rating (say, at least 20 mph over the towing speed) keeps the tire
cool.

The above might be suitable for your situation, if you can find 14" or
15" rims that fit your axle.


--
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

Eric Greenwell wrote:
jcarlyle wrote:


At least we agree that using P rated tires on a trailer isn't a good
idea!


I don't understand why a P rated tire that can travel 15,000 miles a
year at 80 mph on a car would not be suitable for a trailer traveling a
few thousand miles each year at 65 mph (or, for that matter, a trailer
traveling 15,000 miles a year at 80 mph). What am I missing?

I am presently needing new trailer tires, and need to make this choice.
The tire place has Carlisle trailer tires, which seem to have a lot
of negative comments on the internet. Anyone have personal experience
with these tires?



I think it can be done safely in some cases. For example, choosing a
tire with plenty of load margin (say, more than 20%) and running it at
the maximum rated pressure, and towing at 60-65 mph.

Going to a larger rim diameter and lower aspect ratio tire (to maintain
the same outside diameter) with a high speed rating has also been
successful. The lower aspect ratio improves the stability and the high
speed rating (say, at least 20 mph over the towing speed) keeps the tire
cool.

The above might be suitable for your situation, if you can find 14" or
15" rims that fit your axle.

jcarlyle wrote:
Hi, Eric,
Here's a link to a fairly definitive article on trailer tires:
http://www.discounttire.com/dtcs/inf...ionAnxiety.dos
As you can see, it states that trailer tires are indeed optimized for
load, and that for the same dimension an ST tire carries more load
than a P or LT tire.

I found this article on the Subaru site: http://tinyurl.com/9jesg

It varies somewhat from the Discount Tire article. I suspect neither
article fully explains what we'd like to know and I wasn't able to find
a decent third article. Two statements were particularly interesting to me:

ST tires are designed for as soft a ride as possible so they don't
transmit too much shock to the trailer and its contents.

That might explain why an ST tire has the same load capablity at a 10
psi lower pressure than an LT.

Trailer tires typically employ heavier steel or polyester cords and
somewhat lighter sidewall construction than light-truck tires, and
trailer tires typically run lower air pressures than their truck
counterparts. This gives ST tires good load-carrying capacity, but
with the desired softer ride. ST tires also have the advantage of
rubber compounds that are specifically designed to resist
deterioration from the elements, including sunlight and ozone, during
extended storage.

I was very surprised at the Discount Tire article giving a 3-5 year life
for trailer tires, as I've always heard they were optimized for much
longer life (time) than car tires. A tire that loses 1/3 of it's
strength in 3 years doesn't sound like one I want on any vehicle, and
I'm very skeptical of that number. I know the person quoted is from
Goodyear, but Goodyear sure doesn't say that about their trailer tires.

--
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