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Old 11-26-2019, 09:39 AM   #1
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Sorry - tire inflation questions.

I got rid of the Castle Rocks and purchased Goodyear Endurance load D ST205/75R15 for my Salem 26DBLE. I was running 65psi per the side of the tires. THEN

I weighed the axles separately at the CAT scale.

TT Front Axle. 3060
TT Rear Axle. 2620

Per the Goodyear Load/Inflation chart states inflation for the following weights per tire should be

Front +- 1530 per tire @ 35 to 40psi
Rear +- 1310 per tire @ 30 to 35psi

the Max rating is 2150 @ 65psi

SO if I run the 65psi per the tire am I seriously overinflated?
OR if I run the load/inflation rates am I seriously under inflated?
Confused to the point of inaction.

Another question: has anyone with a similar layout (slide w/ dinette & couch one side and sink, stove, fridge, pantry opposite side) been able to weigh the left and right side of the axles separately?

All opinions are greatly appreciated! Thanks
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Old 11-26-2019, 09:52 AM   #2
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ST tires can and should be run at max cold sidewall pressure. In your case that's 65 pounds.

Underinflated tires are the primary cause of tire blow outs (other than old tires). Sidewall flex = internal friction = increased tire pressure = blow out.

-- Chuck
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Old 11-26-2019, 10:48 AM   #3
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I always go to this post by Roger of RVTireSafety.net (Tireman9 here on FTF) and keep my trailer tires pumped up to the maximum:
RV Tire Safety: "Interply Shear" and other Techno Babble
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Old 11-26-2019, 11:26 AM   #4
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What is confusing to me in your post is 35 -40 pounds the weight is 1530 per tire. According to the Goodyear inflation chart for your tires the 1530 pounds is only at 40 PSI, the load rating for 35 pounds is only 1430. Tire inflation charts are almost always in 5 PSI increments.
The weight goal per tire should be the heaviest axle of the two or 1530 pounds per tire. So by that the PSI per tire is for all the tires would be 40 PSI minimum for the load stated.
Since low tire pressures are the leading cause of tire failures, I believe that one needs a safety margin of at least 10% I prefer a 15 % safety margin.
So I would suggest that all your TT tires should be inflated to 45 PSI minimum for your load.
As others have suggested the maximum sidewall tire pressure is always a good idea for the inflation pressure you should shoot for, since low pressure is the major cause of tire and or heat regulated problems.
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Old 11-26-2019, 11:30 AM   #5
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Quote:
Originally Posted by JVS04 View Post
I got rid of the Castle Rocks and purchased Goodyear Endurance load D ST205/75R15 for my Salem 26DBLE. I was running 65psi per the side of the tires. THEN

I weighed the axles separately at the CAT scale.

TT Front Axle. 3060
TT Rear Axle. 2620

Per the Goodyear Load/Inflation chart states inflation for the following weights per tire should be

Front +- 1530 per tire @ 35 to 40psi
Rear +- 1310 per tire @ 30 to 35psi

the Max rating is 2150 @ 65psi

SO if I run the 65psi per the tire am I seriously overinflated?
OR if I run the load/inflation rates am I seriously under inflated?
Confused to the point of inaction.

Another question: has anyone with a similar layout (slide w/ dinette & couch one side and sink, stove, fridge, pantry opposite side) been able to weigh the left and right side of the axles separately?

All opinions are greatly appreciated! Thanks
I have and each time I do so I find that the weights are pretty much equal or within 30-40 lbs. When retracted most of the slide weight is moved toward the center. Weight of items stored under dinette seats is offset by items in cabinet(s) under counter and sink, Stove, and Refrigerator. Just before my last long trip I total weight on the axles was 6280 lbs with left and right the same at 3140 lbs each.

I use 55 psi as a cold inflation which rises, depending on ambient temperature as I drive.

Load is distributed evenly across the tread and the trailer tows like a dream.

No need to inflate a tire to max (65) just because you go to a higher load range. As long as the pressure is AT LEAST the stated pressure on the certification sticker the tire will carry the load specified.

I opted for the Load Range D tires on my trailer to merely increase the safety margin and the extra 5 lbs does that without compromising the tire's footprint of ability to absorb road shock. At 55 psi my tires can carry around 180# MORE than the rating of the axle (total) and 280# more per tire than the original load range C tires each.

Tires are designed and load inflation tables developed with the following in mind:

Providing enough air pressure to support the load along with a safety margin:

Allowing the tire tread to fully contact the pavement while driving

Keeping the tire from flexing too much and causing excessive heating.

These all went into the development of the load/inflation tables and the number molded on the side of the tire is merely the UPPER LIMIT or DO NOT EXCEED for both pressure and weight, not the suggested pressure.

In reality one can run a load range D tire at the same pressure stated for the OE load range C on the vehicle sticker --------- provided the loaded weight of the vehicle doesn't exceed the weight stated on the sticker.

As for the "run the max", many people are running tires installed by the OEM and you pretty much have to run that to just carry the specified load and have a safety margin (assuming you don't overload and if you don't weight, how would you know).

Added note, you need at least the stated pressure on the vehicle sticker to provide for not just static loading of the tire like you will read while sitting on the scale. You need extra pressure to deal with the dynamic loading that occurs while driving down the road, both for bumps and any side-loading during turns, etc.
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Old 11-26-2019, 11:35 AM   #6
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Quote:
Originally Posted by Chuck_S View Post
ST tires can and should be run at max cold sidewall pressure. In your case that's 65 pounds.

Underinflated tires are the primary cause of tire blow outs (other than old tires). Sidewall flex = internal friction = increased tire pressure = blow out.

-- Chuck
This is not right. You only run max pressure if you are loaded to the max. You should adjust the pressure accordingly.
Mike
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Old 11-26-2019, 11:54 AM   #7
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Originally Posted by JVS04 View Post
......

I weighed the axles separately at the CAT scale.

TT Front Axle. 3060
TT Rear Axle. 2620
.....
My concern would be getting the trailer's front and rear axle weights equal.

Given that the tongue will carry approximately 10-15% of the overall trailer weight, the axles should be equal in load. Based on the above numbers, even with your WDH engaged, I'm guessing that your trailer may be slightly nose down on the ball? The tongue may need to be raised an inch or so to take some of the weight off the front axle and load a bit more on the rear.
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Old 11-26-2019, 11:57 AM   #8
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Quote:
Originally Posted by Chuck_S View Post
ST tires can and should be run at max cold sidewall pressure. In your case that's 65 pounds.

Underinflated tires are the primary cause of tire blow outs (other than old tires). Sidewall flex = internal friction = increased tire pressure = blow out.

-- Chuck
Quote:
Originally Posted by Mike223 View Post
This is not right. You only run max pressure if you are loaded to the max. You should adjust the pressure accordingly.
Mike
Exactly. He's not running underinflated, he's increased the load range of the tires.
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Old 11-26-2019, 12:09 PM   #9
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My concern would be getting the trailer's front and rear axle weights equal.

Given that the tongue will carry approximately 10-15% of the overall trailer weight, the axles should be equal in load. Based on the above numbers, even with your WDH engaged, I'm guessing that your trailer may be slightly nose down on the ball? The tongue may need to be raised an inch or so to take some of the weight off the front axle and load a bit more on the rear.
In reality as long as neither axle and tires are overloaded there's no reason for alarm just because one axle has more weight than the other.

In the OP's case he may have a full water tank and as the water is used it goes to the rear holding tanks. The weight transfer will equal things out.

Yes, hitch height adjustment or tilt angle of hitch head may change the weight distribution but just having a trailer slightly nose down or nose up is not a big issue. When hooked up and ready for the road my trailer's nose is about one inch down. By the second day on the road it's perfectly even as water transfers back. By roughly day 5 I empty holding tanks and fill fresh. Back to about an inch down in the front.
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Old 11-26-2019, 12:43 PM   #10
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It clearly states on the GY Endurance sidewall "Inflate to ?PSI for max load" That right there means that you only need to inflate to ?PSI if your at the max load.
I have 235/80/16 GY Endurance on my TT. I run them at 75 psi. I could run them lower but don't.
GY has a tire inflation chart for ST tires. why would they have a PSI/load chart if you are supposed to run them at max PSI?
https://www.goodyearrvtires.com/pdfs/rv_inflation.pdf
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Old 11-26-2019, 01:08 PM   #11
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Under inflated tire = less than max sidewall cold recommended ??? or less than proper inflation to cover actual load ?? Clearly under inflated = not enough psi to cover load (actual weight) but recommended is big can of worms .. just watch as the opinions come in
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Old 11-26-2019, 01:27 PM   #12
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Old 11-26-2019, 01:32 PM   #13
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And around the tire turns once again. I wonder how many threads there are on this?
Fairly positive this is the first in the history of the Internet.
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Old 11-26-2019, 01:49 PM   #14
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Now if we can just get a gas vs diesel it will be the holy trifecta ....
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Old 11-26-2019, 01:50 PM   #15
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And around the tire turns once again. I wonder how many threads there are on this?
Ahhhh .... 1 billion
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Old 11-26-2019, 02:25 PM   #16
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Most tire threads get out of hand because of old outdated misinformation. Lots of people are clinging to old opinions that don't work with newer technology. A lot of info posted on the net is just a repeat of the same opnions.
Deciding on what to do with your ST tires is as simple as looking up YOUR brand and doing research.
I still see guys posting that you can't drive over 65 mph with ST tires. That myth ship sailed several years ago. Yes some tires are limited to 65 mph, but several are not.
One size does not fit all.
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Old 11-26-2019, 04:34 PM   #17
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Originally Posted by ependydad View Post
I always go to this post by Roger of RVTireSafety.net (Tireman9 here on FTF) and keep my trailer tires pumped up to the maximum:
RV Tire Safety: "Interply Shear" and other Techno Babble



X2. Every tire engineer I've talked to or read has advised, for tow-able trailers, run the tires at max pressure. This includes the guys I talked to at GY when I was working there.
Regarding tire speed ratings. Physics studies prove the faster you go, the more likely your trailer will sway.
Look at a 300 mile drive. At 65 mph, this requires 277 minutes. Towing you will get about 11 MPG (fits my experience). You will burn about 27 1/4 gallons. In the same vehicle on the same route, at 75, it will take you 240 minutes and your gas mileage will probably drop to 9.2 mpg. You'll burn about 32.5 gallons. These estimates are based on studies backed by the US Department of Energy.
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Old 11-26-2019, 05:14 PM   #18
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This is not right. You only run max pressure if you are loaded to the max. You should adjust the pressure accordingly.
Mike
I agree. I run mine at 55 psi which is probably slightly overinflated for the most weight I might have on any of the 4 tires. (Like the OP, my tire's max is 65 psi.)

Running at max pressure when not at max load will make the footprint a bit light at the edges.
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Old 11-26-2019, 05:32 PM   #19
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It clearly states on the GY Endurance sidewall "Inflate to ?PSI for max load" That right there means that you only need to inflate to ?PSI if your at the max load.
I have 235/80/16 GY Endurance on my TT. I run them at 75 psi. I could run them lower but don't.
GY has a tire inflation chart for ST tires. why would they have a PSI/load chart if you are supposed to run them at max PSI?
https://www.goodyearrvtires.com/pdfs/rv_inflation.pdf
Quote:
Originally Posted by SailorSam20500 View Post
X2. Every tire engineer I've talked to or read has advised, for tow-able trailers, run the tires at max pressure. This includes the guys I talked to at GY when I was working there.
I think this is why the confusion and endless debates continue. Who do I listen to.... Goodyear and their publicly posted inflation/load chart, or Goodyear's engineers who should have been the ones who made the inflation/load chart? Goodyear had the whole Mara-bomb set of tires so you would think they would error on the side of caution, yet lower pressures are OK.

Right now I tow at <= 65MPH because my tires are only 72MPH rated. I'll gladly trade 5 gallons of gas to get 40 minutes back and not have to sit in the slow lane with the old ladys, diesel spewing trucks, and other mis-fits who are afraid to drive. Can't afford the GY Endurance yet.

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Old 11-26-2019, 05:41 PM   #20
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Suburban Cleveland to Gettysburg PA several times a year while my daughter was a student at the College and we camped at the KOA. 310 miles. At about 62 mph I could do it on one tank of gas. Anything higher I had to refuel enroute. Time lost refueling killed any time savings with the higher speed.

Trailer tire pressure was, of course, 50psi. Maximum side wall pressure. Who cares if the contact patch is slightly higher, there are trailer tires that just tag along for the ride. You're not steering with them. Nor are you looking for a Town Car ride inside.

Recommend anyone running lower that max sidewall pressure feel their tire temperature after 100 miles. If it's the same as the pavement it's fine.

-- Chuck
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