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Old 04-21-2013, 11:58 AM   #1
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Important - Proper tire pressure & tires for Argosy Minuet 6.7

The tires were purchased new by the previous owner when I purchased my trailer in 2010. The tires are BCT JK42 HI-RUN ST205/175R15 Load Range C made in China. After researching on internet it stated to fill air to 65 psi for same tire but load D. I looked on the tire and it states Max Load 1820 lbs. at 50 psi. So I filled the tire up to 50 psi...is this correct? Are these tires appropriate for my trailer weight?

I looked at the spare tire which is made in USA Diso ST SPORT TRAX F78-15ST Load C ...on the tire it states Max load 1710 lbs. @ 50 PSI Cold but also on the tire it states "Warning to avoid tire explosion never exceed 32 lbs. pressure".

Please tell me how much to fill these tires? Did I fill the tire at 50psi too much?

Your prompt reply is appreciated.

Thanks in advance,

Bill

P.S. I'm new to this trailer stuff even though I purchase it 3 years ago...I just camped in my yard & I'm ready this ready to journey out.
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Old 04-21-2013, 12:31 PM   #2
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You are writing about two different tire brands. The maximum pressure for any particular load range tire (C, D, E, etc.) differs a bit according to type (ST or P or LT, for ex.), but for a Load Range C is it usually around 45-50 lbs. You have to check the sidewall to be sure for a particular tire and then check tables on the internet for how much weight the pressure will support. Why the spare gives two different pressures is beyond me. The numbers identifying the tire are different than the usual numbers telling aspect ratio and tread width. It is hard to explode a tire, but if you drive it at 100 mph in 120˚ with a cold pressure of 75 lbs., I guess you could do it. The tread would probably come off before the tire exploded anyway. At 32 lbs. it wouldn't carry 1,710 lbs.

Load Range D is usually 65 psi and E is usually 80 psi. But you don't have to fill a tire to the maximum on the sidewall. Tire pressure is determined by the weight the tire carries and there are tables to determine that.

Tires are a controversial and confusing issue. Read a lot of tire threads and you will get overwhelmed after a while. Wait a while, and then read some more and eventually you'll come to your own conclusions. Tire Rack has a lot of information on its website too.

You'll notice after a while many of us have ditched ST tires as unreliable and switched to LT (light truck) tires, often Michelins. Some have used P (passenger) tires. With LT's, you usually have to go to 16" wheels.

Your trailer is relatively light compared to newer ones, so P tires may work for you and probably can be found in 15" size. Nobody thinks much about tires when they are new to RVing, but you are asking the right questions and have many discoveries ahead of you. Tires are very important, so it is good you are looking at this now.

Gene
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Old 04-21-2013, 12:40 PM   #3
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I believe if you look closely at the 32# max. It has to do with the max pressure when mounting the tire in order to get the bead seated properly. It is not the pressure related to the load carrying capacity.
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Old 04-21-2013, 12:51 PM   #4
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Originally Posted by TG Twinkie View Post
I believe if you look closely at the 32# max. It has to do with the max pressure when mounting the tire in order to get the bead seated properly. It is not the pressure related to the load carrying capacity.
Really? I always thought that max pressure was required for a max loaded vehicle. Adjust downward slightly for less weight.
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Old 04-21-2013, 01:05 PM   #5
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Important - Proper tire pressure & tires for Argosy Minuet 6.7

Greetings Bill!

Welcome to the Forums and the world of Vintage Minuet Ownership!

Quote:
Originally Posted by ArgosyMinuet View Post
The tires were purchased new by the previous owner when I purchased my trailer in 2010. The tires are BCT JK42 HI-RUN ST205/175R15 Load Range C made in China. After researching on internet it stated to fill air to 65 psi for same tire but load D. I looked on the tire and it states Max Load 1820 lbs. at 50 psi. So I filled the tire up to 50 psi...is this correct? Are these tires appropriate for my trailer weight?
You will want to follow the inflation specifications for your Load Range C tires as installed on your Minuet . . . not the Load Range D specifications as that will result in overfilling of your Load Range C tires. Load Range C, bias ply, ST (Special Trailer Tires) were standard on your Minuet in 1978. I know that my '78 6.0 Metre Minuet weighs in a 3,100 pounds loaded for an extended trip with 550 pounds on the hitch. I have routinely inflated my Load Range C Marathons to 50 p.s.i. and have nevery had any tire related problems on my Minuet.

Quote:
Originally Posted by ArgosyMinuet View Post
I looked at the spare tire which is made in USA Diso ST SPORT TRAX F78-15ST Load C ...on the tire it states Max load 1710 lbs. @ 50 PSI Cold but also on the tire it states "Warning to avoid tire explosion never exceed 32 lbs. pressure".
I suspect that the spare tire is a near contemporary to your Minuet. I purchased my Minuet from its original owner in 2003, and it included the original spare tire as purchased from the Argosy dealer in 1978 . . . that tire was a bias-ply Good Year Marathon in Load Range C with a maximum inflation pressure of 32 p.s.i. Special Trailer tires were comparatively new on the market at the time, and seemed to be something of an unknown to some of the Good Year tire dealers that I consulted when I needed a bias-ply Good Year Marathon F78-15ST in 1980 for my then new Nomad 1720.

Quote:
Originally Posted by ArgosyMinuet View Post
Please tell me how much to fill these tires? Did I fill the tire at 50psi too much?
I don't think that your Load Range C tires are overfilled at 50 p.s.i., but the ride may be rougher than necessary if they are filled beyond what is required for the load. Most of the tire manufacturers provide load/fill charts so that you can adjust the inflation to support the load carried . . . with my Minuet, I am close enough to the the capacity of Load Range C so I stick with the 50 p.s.i.

Good luck with your Minuet!

Kevin
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Old 04-23-2013, 11:25 AM   #6
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Originally Posted by TG Twinkie View Post
I believe if you look closely at the 32# max. It has to do with the max pressure when mounting the tire in order to get the bead seated properly. It is not the pressure related to the load carrying capacity.
TG you are correct. The 32 is the initial inflation pressure to seat the beads.

The inflation to run on trailers would be the inflation shown along with the statement on "max Load" molded in the tire sidewall.
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Old 04-23-2013, 11:29 AM   #7
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Argosy
What tire Load Range and pressure is shown on the tire placard from the RV manufacturer. You should not be lower than that. The precious owner might have bought LR-C to save $ when you should have LR-D.
Also the Max inflation for any specific Load Range might be different if the tire size is different. You may also find that there are som tires out there with non-standard load capacity so you again need to have AT LEAST what is on your placard.
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Old 04-23-2013, 05:54 PM   #8
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Tire pressure is determined by the weight the tire carries and there are tables to determine that.

NOT on a trailer. Trailer tire pressure is ALWAYS sidewall maximum. This is the engineered standard. Ask any tire dealer, or read RMA publications online.

Someone who wants to change their pressure, that's one thing. But the default is sidewall maximum to avoid tearing the tire off the rim as the way a trailer is jacked around in turns as well as in backing. The leverage against the vehicle is powerful.

Do it the right way and keep an eye on pressures and wear. If one wants to change that (risk increase), well, it's their trailer. But expect that problems will occur sooner than later.

.
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Old 04-23-2013, 07:10 PM   #9
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I disagree with the maximum pressure theory.
If you are running Load Range E tires on a trailer that is designed for Load Range C tires. And many people do this. There is NO need to inflate the E rated tires to there maximum rating.
Trailer manufacturers put the cheapest tire they can find on the equipment. As long as they meet DOT requirement.
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Old 04-24-2013, 08:31 AM   #10
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Originally Posted by TG Twinkie View Post
I disagree with the maximum pressure theory.
If you are running Load Range E tires on a trailer that is designed for Load Range C tires. And many people do this. There is NO need to inflate the E rated tires to there maximum rating.
Trailer manufacturers put the cheapest tire they can find on the equipment. As long as they meet DOT requirement.
If you are running Load Range E tires on a trailer that is designed for Load Range C tires. And many people do this. There is NO need to inflate the E rated tires to there maximum rating.
Trailer manufacturers put the cheapest tire they can find on the equipment. As long as they meet DOT requirement.[/QUOTE]
You are correct about the cheapest tire usually being selected. Now if you have changed your original tires from LR-C to LR-D or LR-E and wheels to a set that can carry the increased pressure then you are looking at different set of circumstances.
If your LR-C tires and placard specified 50 psi then changing to a higher Load Range and not also increasing the tire pressure will gain you nothing. It is the air that carries the load not the tire. I have clarified this in my blog.
Tandem axle trailers have unique lateral tire loading. Finite Element analysis of the internal structural loads during cornering indicates that trailer tires see 24% higher shear forces that work to tear the tire structure apart. You can lower, but not eliminate, these forces with lower cornering force which come when you increase inflation pressure.
If you changed your tires and wheels to allow increased inflation then why would you not increase the inflation?
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Old 04-24-2013, 09:05 AM   #11
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If you changed your tires and wheels to allow increased inflation then why would you not increase the inflation?
Since AS trailers like to be treated with tender care will increasing the pressure impart a harsher ride to the trailer? Popped rivets, vibration so on.

Loading Chart.

http://www.goodyearrvtires.com/pdfs/rv_inflation.pdf

Goodyear PSB giving information on how to run GYM above 65mph.

http://www.tirerack.com/images/tires...plications.pdf
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Old 04-24-2013, 09:25 AM   #12
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Running your tires under inflated puts tremendous stress on the sidewalls from all the bouncing and flexing. I bought a 19' Bambi 3 yrs old that the PO had said he kept the tires at 50psi to provide a cushy ride. Soon after, a tire lost it's seal on the rim and deflated. Tire dealer stated that the seal was failing because of the weakened sidewalls.

Have been running Maxxis E inflated to 75lbs with over 20,000 miles on my 25FB and still have all my rivets and good even wear.
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Old 04-24-2013, 12:43 PM   #13
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ST tires have stronger sidewalls to compensate for the lateral forces on trailer tires. When most people went to radial tires from bias ply, they found radials do not have stiff sidewalls*. The ST is a radial with stiff sidewalls. LT radial tires generally do not have such stiff sidewalls**, so there is a reason to use increased pressure in them. It also helps to not do severe turns when backing when the lateral force can be so high that the tires skip sideways, or, worse, break the bead.

Slowmover's beliefs are based on the difference in sidewalls and make sense to me even though I don't run the LT's at maximum pressure. Right now I am between LR D and E—72 psi. I guess that's a wishy-washy approach. I have looked at this through complex guesswork (emphasis on guess), watched tire wear and increased from 68 to 72 psi based on checking with a tread depth gauge.

But tread wear and the effects of lateral force on sidewalls are completely different questions. I doubt there is any good research on these effects comparing LT and ST tires.

Gene

*Radials hold the road better because the tread is less likely to skip on curves—the sidewall is flexible and bends while the tread doesn't lose traction. Bias ply tires Are more rigid and would slide laterally in the same curve. The lateral force has to be expressed somewhere‚ sidewall or tread. If you have too much lateral force, the radial will suddenly loss traction and you will be in a lot of trouble; the bias ply slides more slowly. But for most people this was not a problem. Trailers have different needs and a compromise was the ST radial.

**Michelin Rib tires have stiff sidewalls as I understand it, though how they compare with ST stiffness is beyond me. Some have mounted these on their trailers and like them. They are designed for intracity trucks that put on a lot of miles at lower speeds and get retreaded repeatedly.
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Old 04-25-2013, 02:55 AM   #14
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Quote:
Originally Posted by ArgosyMinuet View Post
The tires were purchased new by the previous owner when I purchased my trailer in 2010. The tires are BCT JK42 HI-RUN ST205/175R15 Load Range C made in China. After researching on internet it stated to fill air to 65 psi for same tire but load D. I looked on the tire and it states Max Load 1820 lbs. at 50 psi. So I filled the tire up to 50 psi...is this correct? Are these tires appropriate for my trailer weight?

I looked at the spare tire which is made in USA Diso ST SPORT TRAX F78-15ST Load C ...on the tire it states Max load 1710 lbs. @ 50 PSI Cold but also on the tire it states "Warning to avoid tire explosion never exceed 32 lbs. pressure".

Please tell me how much to fill these tires? Did I fill the tire at 50psi too much?

Your prompt reply is appreciated.

Thanks in advance,

Bill

P.S. I'm new to this trailer stuff even though I purchase it 3 years ago...I just camped in my yard & I'm ready this ready to journey out.
First, like others, I think the spare tire (F78-15ST) is the original spare - and the original ground tire size. Note that it says the max load carrying capacity is 1710 # at 50 psi.

Second, like others have said, the maximum pressure of 32 psi probably refers to mounting the tire. Read that part again to be sure, because it doesn't make sense to rate a tire at 50 psi that can't be inflated higher then 32 psi.

Third, your current ground tires (ST205/75R15 LR C) say the load carrying capacity is 1820# at 50 psi - which is 6% more than the spare. I think a trailer ought to have tires that are rated 115% of the actual load - and I think trailer manufacturers do not do a good job of providing adequate tires - so I wonder if these tires are enough. The only way to be sure is to weigh the trailer - tire by tire - to see what each tire is experiencing.
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