Tire Pressure

[KneeDeep]

Good morning.
I have a question about tire pressure.

When we picked up our "new to us" '17 Volante 360DB, it came with Castle Rock ST 235 80R 16s (nitro filled) installed.

We towed it home and have been living in it during reconstruction on our house. In preparation to take a trip with it, I found that all four tires were at precisely 65lbs. In that all four were exactly the same, I feel certain they came from the dealer that way.

I'm wondering is there some reason that they would have been pressurized 15lbs low from the required 80?

Thank you in advance for your opinions.

[Dropthejacks]

Are you saying the required 80 psi is what is on the plate on the side of the RV? Or is that the max tire PSI stamped on the sidewall of the tire itself? If the plate says 80 psi and the tires say 65, you have a problem. Someone has installed a tire that probably doesn't meet the load requirements on your RV. If the tire says 80 psi and the tech aired them to 65, the tech didn't know what he was doing and you need to run them up to 80 psi or risk overheating issues and blowouts due to the tire needing the max air pressure to meet its stated load limits. Less air = less load.

[1bigmess]

Read the sidewall to see what the max load and pressure is. ST tires are designed to be run at max pressure. They'll give a rougher ride, but unless the tire manufacturer has a load table to set specific pressures at specific weight loads, and I don't think any do for ST tires, they should be run at max pressure.

[SmokeyWren]

Hey, KneeDeep - and to our campfire,

Originally Posted by KneeDeep

I'm wondering is there some reason that they would have been pressurized 15lbs low from the required 80?

How did you determine that the required PSI in the trailer tires is 80 PSI?

Most Special Trailer (ST) tires are rated at a max 50 or 65 PSI. As 1bigmess noted, trailer tires should be pumped to the max PSI on the sidewall. That means cold PSI, before you have towed the trailer more than a few feet.

Originally Posted by 1bigmess

They'll give a rougher ride, but unless the tire manufacturer has a load table to set specific pressures at specific weight loads, and I don't think any do for ST tires, they should be run at max pressure.

Maxxis posts load/inflation charts for their ST tires. That's the only one I've found recently. But I wouldn't use it for anything except to be sure the weight rating of the tire was more than enough to support the weight on the tire when pumped up to the max PSI on the sidewall.
Trailer Tire Load/Inflation Chart | Maxxis Tires USA

Note that the max cold inflation for Maxxis 13" and 14" trailer tires is 50 PSI (load range C), for size ST205/75R15 the max inflation is 65 PSI (load range D), and you have to go up to at least size ST225/75R15E before you can get trailer tire with max inflation of 80 PSI.

[chboone]

OP says he has ST 235/80R16. Check the bottom of the chart.

Castle Rock Radial Tire

To KneeDeep fill the tires to 80 PSI before towing the trailer any further. Then call the dealer and tell them you want new tires.

[KneeDeep]

Yes, side wall, plate, and tire manufacturers tables all call for 80. I called the service dept and asked if there was a reason they were inflated to 65. They were rather surprised and said absolutely not.

I've already broke in my new Viair and pumped em up to where they belong. Spring brings a new toy budget and Jane will get new Goodyear sneakers.

Thanks all!
And thanks for the welcome!

[KneeDeep]

[UPDATE] You folks are fantastic and I want to thank each and everyone of you. With your help I was able to research the bombs under my 'Jane' and take a couple extra precautionary steps in preparation for our holiday travel.

As it turns out, off door side front suffered a tread separation at 65 mph around Duson, LA 3.5 hours into a 4 hour day. No camper damage, but a good team exercise for the family changing tires and learning about maintenance ( two kids 10 and 11).

Next morning, Goodyear in Lafayette got us in early. Refused to put LT on the camper and insisted on going with the new ST Endurance. 800 miles ( I know, ONLY 800) later I have to say I'm not disappointed.

I hope to post more good news on this redesigned tire. More importantly, I hope to get my money out of them.

Happy Thanksgiving all!
Git yo turkey on!

[KneeDeep]

Also, a lesson learned from advice from a mechanic - Deflate a faulted tire before doing ANYTHING else with it such as removing lug nuts, jacking the wheel etc.

He turned white when he realized I had taken it off the camper, handled it over into the bed of the truck all while fully pressurized and belts hanging out both sides of the fault under the tread.

Deflate first!

[Dropthejacks]

Glad you caught that tire issue early!! I switched to the Endurance this spring. Have about 8 trips and prob 4000+ miles on them. No issues so far, which is what I expected from Goodyear. Combined that with a TST TPMS system and our rides are much more relaxed and worry free now.

[Rednax]

The problem with ST tires isn't the manufacturer or the country of origin.

It's the built-in lack of QC that makes it illegal to use ST on a passenger vehicle.

Good luck with them.

The risk of a single emergency stop and replacement on the side of a busy highway makes the risk unacceptable BEYOND any damage to the TT.

No such thing as ST not so long ago. All we had was LT. There's no significant savings, either.

[SmokeyWren]

Originally Posted by Rednax

The problem with ST tires isn't the manufacturer or the country of origin.

It's the built-in lack of QC that makes it illegal to use ST on a passenger vehicle.

Baloney! Where did you get that? Quality control on a Goodyear Endurance ST tire is the same as on a Goodyear LT or P-Series tire.

It's illegal to use Special Trailer (ST) tires on a passenger vehicle for the same reason it's illegal to use passenger vehicle tires not rated for trailer service on a trailer.

P-series tires are NOT rated for trailer service. Only a tiny few light truck (LT) tires are rated for trailer service, and I don't know of any that are sized for a wheel less than 16" diameter. My favorite trailer tire is the Michelin XPS, but it comes in only a few LT 16" sizes. Goodyear has a competitive tire to the Michelin XPS, but it comes in the same few 16" sizes. My favorite tire for a passenger vehicle is the Michelin LTX Defender, but it's not rated for trailer service.

For a Michelin tire, if it's not included on the MichelinTruck website as an "all position" or trailer service tire, then it's not rated for trailer service. None of the popular Michelin LTX tires are included on the MichelinTruck website.

The ST tires were developed for a reason - the sidewall of tires designed for use on passenger vehicles and light trucks were not strong enough to handle the forces applied to trailer tires when dragging them sideways around sharp turns. ST tires have much stronger sidewalls than P-Series and LT tires. All the tire experts require ST tires for trailer service. None of them recommend using LT tires for trailer service unless the LT tire is rated as an all-position tire. "All-Position" includes steer axle, drive axle and trailer axles. All P-Series and most LT tires are designed for steer and drive axle applications, but not for trailer service.

[babock]

Originally Posted by SmokeyWren

it's illegal to use passenger vehicle tires not rated for trailer service on a trailer.

It's actually not illegal. P series tires are derated 10% if used on a trailer. The problem of course is that a P series tire derated 10% will likely not have enough load carrying capacity so you don't see them used that way very often.

[Tireman9]

All tires sold for highway use in US MUST have a Load / Inflation chart reference to pass the DOT requirements. While the tire company may not have a web site that doesn't mean they do not follow an industry table.

In the US Tire & Rim Association TRA publishes a large book that covers everything from wheelbarrow tires to earthmover tires and even valves and tubes.

To my knowledge, all but a handful of tires use the same table numbers so if you find a MAXXIS or Goodyear table for ST tires the numbers will be the same for other ST type tires.
Goodyear, Bridgestone and Michelin all have tables on their web site.

You can also check my blog for a post with dozen + links to various companies tire information.

It is legal to use P or LT tires on trailers. BUT if you use P type the load capacity must be decreased by dividing by 1.10. I am not aware of any regulation that states that a tire must be marked "for trailer use" for it to be used on a trailer.

I have seen LT tires marked "for trailer use only" which I would interpret as not being as robust as a regular LT tire but there is not DOT category for this application. It is just up to the tire company. They would be the ones best to explain their reasoning.

It is NOT legal to use ST type tires on passenger carrying vehicles and this is because of the higher load capacity which reduced the safety margin.

ST tires do have different and less stringent requirements than LT tires to pass to meet DOT requirements. I don't know if this relates to QC as all St tires must be capable of passing the ST requirements.


To the OP. You can review my blog to learn more about tires and especially more about St type tires.

[Rednax]

Originally Posted by SmokeyWren

Baloney! Where did you get that? Quality control on a Goodyear Endurance ST tire is the same as on a Goodyear LT or P-Series tire.



It's illegal to use Special Trailer (ST) tires on a passenger vehicle for the same reason it's illegal to use passenger vehicle tires not rated for trailer service on a trailer.



P-series tires are NOT rated for trailer service. Only a tiny few light truck (LT) tires are rated for trailer service, and I don't know of any that are sized for a wheel less than 16" diameter. My favorite trailer tire is the Michelin XPS, but it comes in only a few LT 16" sizes. Goodyear has a competitive tire to the Michelin XPS, but it comes in the same few 16" sizes. My favorite tire for a passenger vehicle is the Michelin LTX Defender, but it's not rated for trailer service.



For a Michelin tire, if it's not included on the MichelinTruck website as an "all position" or trailer service tire, then it's not rated for trailer service. None of the popular Michelin LTX tires are included on the MichelinTruck website.



The ST tires were developed for a reason - the sidewall of tires designed for use on passenger vehicles and light trucks were not strong enough to handle the forces applied to trailer tires when dragging them sideways around sharp turns. ST tires have much stronger sidewalls than P-Series and LT tires. All the tire experts require ST tires for trailer service. None of them recommend using LT tires for trailer service unless the LT tire is rated as an all-position tire. "All-Position" includes steer axle, drive axle and trailer axles. All P-Series and most LT tires are designed for steer and drive axle applications, but not for trailer service.

Hey, Smokey,

A young whippersnapper like you doesn’t have the memory that we all used LT for decades until this category of tire (ST) showed up.

1) It’s a great way to keep worn out manufacture machinery running awhile longer, (is one hypothesis).

2) There was no “need” of ST is important to note. (Those two fit together).

ST may be adequate for the open construction trailer that sits around.

That trailer may not ever travel far. Around a metro area, basically. Not high-speed and long distance.

It’s faults aren’t then in evidence so often. And it may be used roughly enough that failure is considered acceptable. Why not a cheap tire? Makes sense. For that use.

QC is the cost savings.

ST is notorious for leakage. We will see if GY has that beat. Probably accounts for a high % of failures on its own.

Whoever wants them can have them. Good LT tires don’t cost much more.

Go make some comparisons. Data tables, and in person.

Get those TT individual wheel weights with the WD cranked down. Run the numbers. Give yourself 15% minimum reserve. See what other tires work.

Try the LTL forums where men use one ton pickups and similar to make their living hauling freight on open trailers. That’s an acid test. Tight margin for those men. Low cost with good return vs problems. Jimnlin made that a career for a number of years, and he’s the man to ask about what’s working in the commercial world.

If one avoids a single incident of having to stop to change a flat, it was worth it, in my less than humble opinion. Being hit while on the side of the road is NOT uncommon.

Because if that isn’t a sobering thought, I don’t know the meaning of the term.

This is before damage to the TT. One TT like mine that’s $6-8k due to shear.

The proper LT will last longer and is built to a higher standard. That’s the rule of thumb that works.

I can get a comparable Bridgestone for maybe another $25/ea vs GY (itself a brand I quit buying more than 25-yrs ago).

Or, as I’ve spent almost fifty years with TTs and more than twenty driving Class 8, I also have a very low tolerance for poor tire performance.

I do willingly spend another $325 to get (4) Bridgestone R250. More than I need, no question. Same lot, and balanced to Lexus/Mercedes spec on a Hunter GSP-9700. Or it’s rejected. Some need no weights at all, it’s a great tire. The dealer knows me. As do his techs. My pickup tires last over 100k with well more than 4/32’s remaining. (As do brakes, etc).

Those who buy my TT type intend to travel. 100k miles In under ten years is nothing. The next ten might be more. I cannot guarantee success, but I’ll load my box with the tools best proven.

Because

There’s other places to save. They just don’t happen to involve 65-mph gambles.

Making life easier on any set of tires with a leaf-sprung suspension by upgrading to a shock absorber kit plus better equalizers and cross-bracing is smart money. Centramatic balancers, too. It’s how premium TTs used to be built if they didn’t use torsion axle (still the best).

Take the shock load off of the tires, first.

I’ll tweak your tail again in closing and say, hang in there young guy!