Revived Trailer Tire Thread (formerly on the 5th Wheel Forum

[CapriRacer]

OK, I'll try this again but with a different tack.

I am of the opinion that ST tires should have a 15% reserve capacity (85% of the load at a given pressure) in order to be reasonably sure they won't fail. There are a couple of ways of estimating what the actual load is on a given tire of a trailer, but the best way is to actually measure each tire. The RMA has a procedure to follow:

http://www.rma.org/publications/tire_service_professionals/index.cfm?PublicationID=11516

I am of the opinion that this 15% reserve capacity is likely to require higher load ranges and larger sized ST tires - or both. And maybe even a step into LT type tires - and here is where it gets tricky.

While I feel uncomfortable recommending that LT tires be loaded to their maximum load, that is in essence the result. I feel uncomfortable with that because I don't have enough experience to say it with confidence. However, I have no hesitation in recommending replacing ST tires with LT tires if it can be done with enough clearances around the tire.

A couple of other points:

ST tires can be inflated 10 psi over the maximum pressure listed in the sidewall of the tire - and I'd recommend that if you can't get to a 15% reserve capacity.

Recent bulletins from the tire industry indicate that tires degrade simply due to time. The age of a tire is important even if the tire is unused.

There is some disagreement over how to best express this age limitation,
but my take is:

If you live in a hot climate (AZ, CA, NV, TX, and FL) then the limit is six years. If you live in a cold climate (MN, ND, WI, MT, etc), then the limit is 10 years. States in between are ..... ah ........ in between.

A rule of thumb for estimating if you need more load carrying capacity:

Check the cold (ambient temperature) tire pressure before starting off. Measure the inflation pressure after an hour of driving.

If the tire pressure build up is less than 10%, it's OK. If the pressure build up is between 10% and 15%, then continue to monitor until you are sure it is not above 15%. If the pressure buildup is 15% or greater, add load carrying capacity (and one of the ways to do that is to add pressure). For ST and LT tires, NEVER use more than 10 psi over the sidewall pressure.

Any questions?

[Cox89XJ]

I’m the one that post the picture of the failed Chinese tire on page 21 of this thread. It was a Mission ST225/75R/15D rated radial tire. If cruising at 65 to 67mph is abusing, yes it was abused. It definitely was not overloaded or run low of air. When I went to a B F Goodrich Commercial TA in size LT225/75R16E rated tire, I have not had any more tire problems. Still cruising between 65 and 67mph. Out of the five tires I had to fail, they all looked like the one in the picture, but one. It’s the one that came apart just North of Birmingham. No doubt, it started the same way with tread separation. The ST’s are like a heavy duty inner tube compared to a LT tire. Mine were anyway. We usually take at least two pretty long trips every year. (400 miles one way or more) Like I’ve said on short trips the tires don’t have time to build up a lot of heat so in my Opinion, that is why some people get by with the ST’s. Short trips or not very heavy campers.

[Chris3]

I believe the Goodyear Marathon ST has only a three year warranty! Chris

[Slowmover]

Excellent thread. Glad to see you over here also, CapriRacer!

[Tireman9]

Francesca Knowles wrote:

azjeffh wrote:

Francesca Knowles wrote:


WHEN should trailer tires be replaced?

Think the OP's first post answered that.

CapriRacer wrote:



but my take is:
There is some disagreement over how to best express this age limitation,
If you live in a hot climate (AZ, CA, NV, TX, and FL) then the limit is six years. If you live in a cold climate (MN, ND, WI, MT, etc), then the limit is 10 years. States in between are ..... ah ........ in between.

I'd like to hear from Capriracer if in his opinion those rules hold true for all trailer tires regardless of type, especially including ST's.

Thost age "limits" are simple guidelines and not hard rules. Noone will ever claim that all tires are oK for 2567 days and that they will fail on day 2568. Just too many variables.

When you buy milk it has a date on it. Is the milk always good up to that date? Is it always bad after that date.

Read my post on Potato Saladalad for more understanding.

[Tireman9]

ExRocketScientist wrote:


Snip

CapriRacer -- can we work up a chart?

Are you suggesting a chart that has the information in TRA book and that is already on most tire company web sites? Not sure if I understand the need. Trying to duplicate the info in all the web sites to ensure that any individual outliers are covered will be a real challenge.

I don't have access to ST type tires but maybe someone at a campground could do a quick walk around to see if they can answer this question.

Do Some, Most or All LT tires you see include the "Service Description" This is the number letter combination after the size with the number being the Load Index and the letter being the Speed Symbol.

Do Any ST tires have a Service Description?

In Passenger & LT tires the intent was to make it easy for an owner to get replacement tires as all that they should do is read the Service Description and be sure the replacement tires have a number equal or greater than the OE tire and a Speed symbol equal or faster than OE.

[Chris3]

Francesca Knowles wrote:

azjeffh wrote:

Francesca Knowles wrote:


WHEN should trailer tires be replaced?

Think the OP's first post answered that.

CapriRacer wrote:



but my take is:
There is some disagreement over how to best express this age limitation,
If you live in a hot climate (AZ, CA, NV, TX, and FL) then the limit is six years. If you live in a cold climate (MN, ND, WI, MT, etc), then the limit is 10 years. States in between are ..... ah ........ in between.

I'd like to hear from Capriracer if in his opinion those rules hold true for all trailer tires regardless of type, especially including ST's.

Maybe three sets? According to most posters here 3 years is pushing ones luck! Chris

[Francesca_Knowl]

azjeffh wrote:

Francesca Knowles wrote:


WHEN should trailer tires be replaced?

Think the OP's first post answered that.

CapriRacer wrote:



but my take is:
There is some disagreement over how to best express this age limitation,
If you live in a hot climate (AZ, CA, NV, TX, and FL) then the limit is six years. If you live in a cold climate (MN, ND, WI, MT, etc), then the limit is 10 years. States in between are ..... ah ........ in between.

I'd like to hear from Capriracer if in his opinion those rules hold true for all trailer tires regardless of type, especially including ST's.

[azjeffh]

Francesca Knowles wrote:


WHEN should trailer tires be replaced?

Think the OP's first post answered that.

CapriRacer wrote:


There is some disagreement over how to best express this age limitation,
but my take is:

If you live in a hot climate (AZ, CA, NV, TX, and FL) then the limit is six years. If you live in a cold climate (MN, ND, WI, MT, etc), then the limit is 10 years. States in between are ..... ah ........ in between.

[FastEagle]

CapriRacer wrote:

FastEagle wrote:
My RV trailer is a 37'1" fifth wheel, manufactured by Keystone. It's certification label lists the GVWR as 14,100# and the two axles with a GAWR of 6,000# ea. Since early to mid 2006 the trailer has been fitted with Power King TowMax STR tires rated at 3520# @ 80 psi. I'm currently on the second complete set and they are always aired to 80 psi before going down the road on them.

Tire Size

FastEagle

As a tire engineer, I note the following:

If we assume that the tongue weight is supposed to be 15% of the GVW, then 85% is supposed to be carried by the tires - that's 11,985#. So the 6K axles are - on paper - ever so close to being overloaded. I'm sure everyone is aware that tire loading isn't the same for each axle - and I'm sure everyone is aware that the loading won't be the same side to side. So the entire picture here makes me nervous.

The good news is that the tires are rated substantially above the GAWR.

Question for FE: Are these the original tires? If not, what was?

Our pin weight hugs 18% throughout GVW and has - on occasions - been as high as 2700#. (Our washer/dryer is just forward of the axles on the main floor level. All newer models are in the forward bedroom closet.)

OE tires were GY Marathons sized ST235/80R16D - made in the USA.

Keystone has sort of quit up-dating the Everest specs because it’s a discontinued model but in the reference you can see the tire sizes.

2003 Everest specs

FE

[ExRocketScienti]

CapriRacer wrote:

ExRocketScientist wrote:
This is exactly the information I would like to put in a chart. For all of the LTs that are readily available in the marketplace with a tread appropriate for trailer use (FastEagle would be a big help in coming up with a good list), find out what the load rating is of an ST tire of the same size (even if not available in the marketplace).

Just doing a quick calculation here -- 1.09 x 3042 = 3315 (rounded down to the nearest pound). At 12% that would be 1.12 x 3042 = 3407 pounds. At 13% 1.13 x 3042 = 3437. So it might be that an LT235/75R16 LRE is a direct replacement for a ST235/80R16 LRE (Goodyear Marathon 3420 lb) if the ST235/75R16 LRE is 13% or more than the LT235/75R16 LRE. But it wouldn't be a replacement for the Towmax that FastEagle uses which is 3520 pounds. That is why having accurate numbers here would help.

CapriRacer -- can we work up a chart?

Ah ...... yeah, but why? There are a ton of LT size possibilities, and I'm hoping you're not going to try to cover all of them.

No, not all of them. There couldn't be more than a dozen in 16" or smaller rims (I'm thinking this should only cover 14", 15", and 16" rims -- 5 or 6 tires in 16", 2 in 15" that I know of. I'll have to work with FastEagle on 14" -- perhaps he may be able to come up with one or two more in the 15").

[CapriRacer]

ExRocketScientist wrote:
This is exactly the information I would like to put in a chart. For all of the LTs that are readily available in the marketplace with a tread appropriate for trailer use (FastEagle would be a big help in coming up with a good list), find out what the load rating is of an ST tire of the same size (even if not available in the marketplace).

Just doing a quick calculation here -- 1.09 x 3042 = 3315 (rounded down to the nearest pound). At 12% that would be 1.12 x 3042 = 3407 pounds. At 13% 1.13 x 3042 = 3437. So it might be that an LT235/75R16 LRE is a direct replacement for a ST235/80R16 LRE (Goodyear Marathon 3420 lb) if the ST235/75R16 LRE is 13% or more than the LT235/75R16 LRE. But it wouldn't be a replacement for the Towmax that FastEagle uses which is 3520 pounds. That is why having accurate numbers here would help.

CapriRacer -- can we work up a chart?

Ah ...... yeah, but why? There are a ton of LT size possibilities, and I'm hoping you're not going to try to cover all of them.

[Chris3]

LostinAZ wrote:
I think the lists are overlooking two additional critical items. Who is the manufacturer and where was the tire built!

Well if you are going to get picky like that, you should include the type of tire! Car, Truck or Special!!!

Chris

[LostinAZ]

I think the lists are overlooking two additional critical items. Who is the manufacturer and where was the tire built!

[Francesca_Knowl]

NHIrish wrote:
To the educated tire posters here, thanks for all this info...you do us all a great service, but my eyes hurt.

Can we sum it up for those of us that really don't want to get into the science of tires. What do you say to this?

1. Buy tires of a load rating sufficient to carry the load you have.

2. Allow a safety margin in the tire you choose (For me that is a G rated tire rather than the factory E rated tire on my 7000 lb axles).

3. Ensure that the valve stem used is appropriate for the pressure rating.

4. Keep your tires inflated to the max pressure rating for the tire.

5. Check said pressure frequently.

6. Don't overload or underinflate.

Does that cover it?

Thanks for starting a "boiling down" process!
My eyes hurt, too...

Might it be appropriate to include some kind of heads-up about paying attention to the date of manufacture so that one can be assured that the new tires are as "new" as possible?

Which brings me to a question to which I'd much appreciate a concise answer that might serve as a preface to the above list:

WHEN should trailer tires be replaced?

Seems to me that visual inspection/penny tests aren't right for tires that are intermittently used...how does one know that it's time to take the plunge?

[Francesca_Knowl]

NHIrish wrote:
To the educated tire posters here, thanks for all this info...you do us all a great service, but my eyes hurt.

Can we sum it up for those of us that really don't want to get into the science of tires. What do you say to this?

1. Buy tires of a load rating sufficient to carry the load you have.

2. Allow a safety margin in the tire you choose (For me that is a G rated tire rather than the factory E rated tire on my 7000 lb axles).

3. Ensure that the valve stem used is appropriate for the pressure rating.

4. Keep your tires inflated to the max pressure rating for the tire.

5. Check said pressure frequently.

6. Don't overload or underinflate.

Does that cover it?

Thanks for starting a "boiling down" process!
My eyes hurt, too...

Might it be appropriate to include some kind of heads-up about paying attention to the date of manufacture so that one can be assured that the new tires are as "new" as possible?

Which brings me to a question to which I'd much appreciate a concise answer:
WHEN should trailer tires be replaced?
Seems to me that visual inspection/penny tests aren't right for tires that are intermittently used...how does one know that it's time to take the plunge?