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Old 05-19-2015, 08:19 AM   #1
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Tire Pressures and Tire Temperature

Having just installed new 16" wheels on my 2015 Serenity, along with the Firestone Transforce LT225/75R16, I am attempting to decide on the correct tire pressure and how to determine this.

In ambient temperatures of 80 F, at no time was the tire more than warm. Even with 30 - 40 mph sideways gusts of wind over several hundred miles, the tires and wheels remained only warm to my hand, never hot enough to prevent touching.

My question is, can one determine the correct tire pressure based upon how arm the tire gets in use? It would seem to me, if the tire were under inflated, it would become much warmer, way to hot to touch. Correct inflation would result in the coolest running temperature.

Mine are at 65 PSI currently and I am thinking this is the correct pressure, but would like the experience of others with 16" wheels/tires.
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Old 05-19-2015, 08:44 AM   #2
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Determining the correct tire pressure has to do with two things. 1. Ability to carry the load. 2. Tire wear. The more pressure the more load the tire can carry. The other factor is tire wear. Under inflated tires will wear more on the two outside edges of the tread. An over inflated tire will wear more in the center of the tread. Find a tire that can carry the load and be inflated properly to minimize wear. When you have both of these points covered tire temp will take care of itself. You can also get tire monitors that check pressure and temp in real time while you're driving and display on a screen in your tow vehicle.
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Old 05-19-2015, 09:25 AM   #3
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We use 16" Michelins at 65 psi. Maximum pressure is 80 psi. We have not seen a temperature differential at either pressure using an infrared temp gauge on the outside of the tire.

Arguments for lower than 80 psi pressure include better trailer braking (especially when the roads are wet), less damage to your Airstream from rough roads, and because published load inflation tables indicate it is correct (although these tables may not specifically state the if tire used for a trailer).

Arguments against lower pressure include less trailer sway resistance, and possible internal belt separation with tandem or triple axle trailers due to side pressure (scrubbing) when turning.

We have felt no sway tendencies (possibly due to our PPV style hitch) and are not aware of any tread separation, neither are obvious but that doesn't mean they are not happening.

So as usual safety arguments can be made for either method, primarily better trailer braking vs. better sway resistance. Rough Airstream ride or a trailer tire blowout from separated belts are more about trailer damage than safety, but certainly a concern. And there are those who will argue against LT tires on our trailer, but Airstream offers them as an option and standard on some Airstream models (Classic and EB).

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Old 05-19-2015, 10:17 AM   #4
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Tire pressure is a function of LOAD and nothing else.

load your trailer as you would when going camping and take it to a Cat scale. Weight the trailer while hitched to the TV.

Use that weigh and refer to this chart and your tire size to determine the tire pressure. It is not harmful to run a slightly higher pressure, that will cause ware on the center-line of the tire, nut generally acceptable. It is extremely harmful to run a lower tire pressure, that will cause heat and tire failure.

The MAX pressure printed on the sidewall of the tire is just that, the max the tire can be pressurized to. It has nothing at all to do with the correct tire pressure for a given load.

As far a running temperature. You should be able to put your hand on the tire and hold it there. The one thing you should consider is if you have been running for some time with one side facing the sun you can expext to see a 5 to 10 degree difference side to side.

If I want to check tire temperature I try to coast into a rest area with out using the trailer brakes. This ensures that the brakes are not influences things. If you encounter a hot tire check the wheel web to be sure that heat is not coming from a brake drum or bearing problem. If you have a hot tire, one you can't touch and hold, get it changed because it will blow shortly there after.

I run my E rated 16s at 45 lbs. and that id 10 lbs over the chart recommendations based on the weight. I do that to be able to run in on 5 tires if i have to remove one and still be within the recomemdations.
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Old 05-19-2015, 10:30 AM   #5
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There are tire load charts and Goodyear should have a set of those. It will show pressure and load for those pressures.

As to temps do you have a TPMS system? I have the TST system. On my 25FC with internal sensors I used to see a 30 degree over ambient temperature when driving on the interstate. I have externals on my new Classic and don't have enough experience with them to see how they report though I expect it to be different. Probably lower based on comments on the forums.
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Old 05-19-2015, 11:40 AM   #6
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Tire pressure is typically listed in two places, on the tire sidewall and in the owner's manual.

To start with, it's always a good idea to follow the instructions in the owner's manual. From there, adjust tire pressure according to load and driving conditions. That means you hafta pay close attention to load and how your trailer "behaves" on the road.

With the exception of max pressure, it's MHO that air pressure vs load charts are nothing more than "recommendations" or "suggestions." As a consequence, where the rubber meets the road (pardon the pun) is all about good judgement and common sense. Oftentimes, a few PSI up or down can make all the difference in the world.

An important thing to remember is that tires are an important part of the suspension that driver/operator can adjust up or down to fit a particular need or preference.

Maximum PSI, whether listed in the owner's manual or tire sidewall, is just that, max pressure. Just because it says you can, doesn't mean you should run tires at max pressure. So if tire sidewall says 65 PSI and the owner's manual says 45 PSI, it's always a good idea to start by following the owner's manual and learn to make adjustments according to load and driving conditions; and use tire charts as a guide.

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Old 05-19-2015, 12:09 PM   #7
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I don't mean to butt in on Tommie's thread, but this is my problem as well and I'm thinking two birds with one stone might apply here. If I'm wrong let me know.

I too have just installed new 16" wheels and tires on my 1992, 29' Excella. I was running 15" ST tires, but after experiencing a double blowout on the curb side and the damage a tread separation blowout can cause I decided I'd better do something different.

Up until the blowout I was woefully ignorant when it came to tires. With the help of this forum I found my way to the information I needed to move to 16" LT tires. So, now I'm in the same dilemma as Tommie. What inflation do I need to be using. My Michelin LTX MS/2s have an 80lb Max Cold pressure rating, but I question if that is what I should be running them at. I called the Michelin helpline the person I spoke with was very nice, but not much help. I also called Airstream Tech help and was told they recommend the max pressure of 80lb, psi. I'm skeptical about this being correct. Tire pressures for vehicles are rarely the max pressure. My AS loaded (including fresh water) weight is about 7,300 per the PO (I acquired the Excella in 2012), but I have not weighed it myself. This is something I'd like to do right away, but I'm a bit unsure how to do it. Also, I can't seem to locate a Load and Inflation Chart on the web that seems appropriate.
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Old 05-19-2015, 12:15 PM   #8
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I have 16" Michelins. After reading way more than I ever thought possible on the subject and trying 70, 75, and 80psi over the last 3 years, I have decided on 80 psi. I note no difference in ride or durability of the AS components regardless of the 3 pressures. After digesting the two tire experts' threads and posts, considering their recommended load margins, I think 80 psi is best for me. I have 7600 - 8000 pounds on the axles, although I haven't weighed the four corners individually.
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Old 05-19-2015, 12:15 PM   #9
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Tire Pressures and Tire Temperature

I have run 68-70 psi on my 16'Michelins for the last 15000 miles.I have even tire wear and the trailer rides smooth.my trailer is a 28ft International CCD.


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Old 05-19-2015, 12:30 PM   #10
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http://www.goodyearrvtires.com/pdfs/rv_inflation.pdf

With a quick look, i can't find a US Tire and Rim load/inflation for your Firestone tires--you may need to call the company if you can't find on line. But, above is a load chart for Goodyear tires used in the RV environment. The ST or LT tires is what you would be interested in. As posted above, Under-inflated is where you never want to be. Just know your RV weight and use the chart for your tire's proper inflation. Most companies recommend a minimum PSI buffer. I think it's 10% above chart numbers. Personally, I run close to max sidewall (75 psi in "E" rated ST tires) all the time. That is way over the 10%, but my 30FC rides smooth at 75 psi and tires run maybe 10 degrees above OAT.
Especially, if you have not weighed your RV--and that means each axle--be sure you have more than enough air to boost your load capacity well above what you might weigh. Remember WD hitches add some weight to the trailer's wheels and if you are not running a level trailer, that will affect the low side axle and wheels. TPMS is worth the money. Tire Minder is what I use and is well priced. Good customer support, etc.
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Old 05-19-2015, 01:14 PM   #11
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Can anyone post links to a thread/s on how to weight a TT (Airstream) including the individual tires? I've not done this before, and am a bit intimidated by the process.
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Old 05-19-2015, 01:16 PM   #12
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Tires of a given size are made to Government standards and thus the Goodyear inflation chart can be used for Michelin, Firestone or others. For some reason Michelin used to post a chart for smaller tires but now only posts for truck and larger tires.

Sorry for not posting the link above but I see someone has done so.

One thing to keep in mind. The tire pressure posted on the TB door jam is a general catch all written by a lawyer and has nothing to do with reality. Likewise the pressure listed on the trailer. The scale is the only thing that determines the tire pressure if you place value on the years of engineering research.

Almost all trailer delivered in this country are delivered with marginal or substandard tires from the factory. Thus the VERY LONG THREAD about Marathon tire failures. Another consideration is those factory trailer tires are limited to 60 mph. If you travel at or below that speed then you may be OK.
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Old 05-19-2015, 01:19 PM   #13
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I also use 80 psi on my Michelin's. Again I have a very heavy 30' slide out unit and feel from a load standpoint alone, the 80 psi that I do is warranted. I've had belt separation on the original D and replacement E ST tires, even though I have towed no faster than 65 mph and have kept pressures up to recommended specs on those tires.

We have a couple of guys here on the forum who are tire professionals who work in the industry. They both have noted that in a tandem or tri-axle mode, LT tires are operating in a different environment that they usually do on a 4 wheel truck. LT tires don't have the same construction as an ST tire which have side walls built to resist the lateral forces incurred when used on a trailer. While they both encourage weighing your trailer, they also note that additional air pressure may be justified to stiffen up those sidewalls on LT's. Tires should have a minimum reserve of 15% of their max load capacity (based on weight capacity of the tire inflated to proper pressures).

Unfortunately I have seen no conclusive evidence here on the forum that LT tires perform better with load related pressures vs. inflating to maximums on the tire itself. I do know in the case of my van (that uses the same size tires as my Airstream), the manufacturer (GM) recommends lower than maximum air pressure dependent upon load. For example top end recommendation for my front tires for my van under max load is 55 psi with the rears at 80.

In many cases Airstream is going to recommend 80 and that I think is entirely based on the assumption that you are not going to weigh your trailer and the fact that it is an LT tire, not an ST. Under inflation is a much more serious condition which can lead to a blow out, damage to the trailer, and possibly other handling situations. Their assumption most likely is that a higher inflation factor has less liability to them vs giving you a too low recommendation.

You can read all the threads here and you will find that no one will give you the final answer. You can feel good though that so far, the record on LT tires on Airstreams is good and at this point we have had owners that use pressures lower than 80psi. Trailer owners talk a lot about the issues with ST tires, so this is just not an Airstream issue. Some 5th wheel trailers now come standard with 16" LT tires and on those which I have seen at RV shows, their manufacturers recommendation's have been 80 psi.

I think the trailer industry as a whole always recommends max inflation for tires and again I really believe it is the fact that most folks truly don't know the weight of their trailers, especially when carrying liquids in the holding tanks. The tire manufacturers aren't going to help you much since they are going to tell you to use ST tires and not to use LT's since they aren't designed for trailer use. Those inflation tables technically don't factor in trailer use which according to the tire professionals, has some bearing on the inflation factor.

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Old 05-19-2015, 01:36 PM   #14
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Quote:
Originally Posted by Re-Pete View Post
Can anyone post links to a thread/s on how to weight a TT (Airstream) including the individual tires? I've not done this before, and am a bit intimidated by the process.
Go to any truck stop and use the Cat scale. If you trailer is set up right, sitting parallel to the ground when hitched, you should only need way all axles at once. If your trailer in not riding parallel to the ground get that corrected first.

Most of use generally weight the axles of the TV empty and then weigh them and the trailer while hitched. This lets us know how the hitch is transferring weight. There are 3 plates at the scale and you can position your rig to weigh the TV axles and the trailer at the same time.
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