Air Compressor - How Big do you need?

While air volume output might be a consideration, IMO if you are properly inflating your tires and properly (TPMS) monitoring inflation I don't understand how anyone can get in a position of needing more than about 5 psi unless you have an active leak.

If you are only adding 5 psi then tou do not need to worry about how long it would take to inflate a 275/80R22.5   All you need is a compressor rated for more psi than what your tire needs. I would think that a 150 psi rating for the compressor fro tires needing 125 psi   or 100 psi rating for 80 psi tires would be enough.

As I have covered a number of times in this blog, I recommend your cold inflation pressure to be at least 10% above the minimum needed to support your actual measured tire loading (Minimum inflation would be based on the heaviest loaded tire on any axle or lacking individual tire loading numbers,  then using an assumed 53/47% side to side split for motorhomes and trailers with big slides or residential refrigerators and at least 51/49% load split for smaller trailers)

So assuming you have LR-C or LR-D tires you would be inflating to 50 or 65 psi with your TPMS warning set to no lower than 49 or 64 with your minimum inflation in the load tables being 45  and 58. So how would you ever need to add more than 5 or 6 psi assuming you let your tires get that low? Why not do your "top-off" as soon as you need 3 psi? Now you do need to consider the 1 or 2 psi difference between your calibrated hand gauge and the TPMS reading. I set the warning based on the TPMS reading AFTER setting the tire using my certified hand gauge.

Yes pressure changes with temperature (about 2% for change of 10°F Temperature)  A change in morning temperature of 40F from day to day is unusual and that would only result in a pressure drop of 5 psi on your LR-D tires.

Motorhomes should be running a +10% margin on air pressure based on the measured tire loading which means there would need to be a 50°F drop in temperature for them to need to add 10 psi (assuming a 100 psi minimum).

If you need to add more than 20% (20psi) of the needed pressure in your tires with steel body ply, that means you have technically been operating on a "flat" tire according to tire industry standards and you should have a professional inspection and have them re-inflate your tires AFTER the reason for the sir loss was identified and repaired. Large 19.5 and 22.5 tires should only be re-inflated in a cage just in case there was damage to the steel body cords which can lead to an explosion due to zipper rupture.

LR-E (80 psi polyester body tires) as found on most Class-C and some larger trailers need to consider the above information and adjust for their higher cold inflation numbers. I would consider a 20% drop to put you in the safety cage re-inflation level if you drove on the tires when that low. While they are not likely to suffer a true "zipper" failure from fatigued steel body cords, there can still be internal structural damage to your tires.

Bottom Line:  Monitor your tire pressure and don't let the pressure drop more than 10% before you re-inflate your tires. Know why the pressure dropped and if not due to a drastic change in temperature overnight, inspect for leaks. I find that spray cleaner like Windex or other cleaners tend to foam at the location of the leak.

##RVT934

How I avoid problems with Dualie tire hose extenders.

The key to avoiding problems with a hose or any type of valve extension is to be sure the outer end is

 S O L I D.

Some hose kits come with small brackets that can be pop-riveted to hub cap. Others have brackets that attach to lug nut.
People often fail to support the hose or bracket when checking or adding air. The force needed to get a good air seal is enough to bend or loosen the hose mounts. or they inadvertently twist the hose and end up with a leak where the hose screws onto the metal valve.

You need to hold the outer end of the hose firmly to prevent movement or twisting or you can expect to eventually have problems.
In THIS blog post, you can see my set-up (42,000 mi) w/ no leaks or failures.

Since I run a +10% psi margin over the minimum pressure I need on my Class-C based on 4 corner weights and since I always run TPMS (that I have tested) I simply use the TPMS to tell me the inflation each morning before I start out.
During a cross country trip OH > OR > OH over 7 weeks I only needed to add air once so since I am not messing with the hose extensions, I am not pushing on their mounts or applying a force that might result in a slow leak.

If/when I ever do need to remove a sensor to change a battery or add air, I ALWAYS spritz Windex to check for any leaks after I am done.

##RVT926

"Only" drove 750 miles with companion dual tire low on air

Quote:

Originally Posted by Charlie What should I do? I had checked tire pressure the day before and only drove about 750 miles when the right rear inside duel blew resulting in damage to the MH and the tow. Only the side wall blew and the tire stayed on the rim. This is the first time in over 25 years of RVing that I have ever had tire trouble. I only had about 14,000 miles on these tires that are less than 2 years old. I bought the best tires they recommended. I will not say the brand but it begins with M. I had pressure set at 120 psi and they were filled when the tires were cold and had not been driven for over a month, Should I be concerned about the other tires?

Should you be concerned? It depends. Why did the tire fail? If the failure was a sidewall flex failure (sometimes called a "zipper") from running low then there was most likely an active leak, i.e. puncture or leaking valve core would be on the top of my list. In this case the other tires are no more likely to fail next week than they were last week with one exception to be covered in a moment.

If you take the failed tire to a heavy truck tire dealer for the brand involved they should be able to confirm the mode of failure.

Since you were not running a TPMS (tire pressure monitoring system), all we know is that probably sometime between checking the tire pressure and 750 miles later (2 days?) one tire had lost most/all of its air. We also know that the outer dual was run with possibly 100% overload so it probably sustained internal structural damage that shortened its life (months or years). Since we do not know how many miles at what % overload, it is impossible to predict -- so the suggested best practice is to replace the companion dual.

One thing we can do is to use this as a learning experience. With a TPMS a driver would get early warning and many times can stop before a tire is damaged and, by extension, avoid damage to the RV and even not damage the mate in a set of duals. A single warning in the life of a TPMS (years) could save much more than the cost of the system.

Now as to the other possible reason for a tire to lose air. It is possible for a piece of grit to get into the valve core and allow air to leak. I suggest you review the posts on "Valves" (list to the left) and you can see an actual example of a leaking tire and the grit that caused it. So, as I have pointed out in the past, the very act of checking air pressure can sometimes result in a leak and potentially a failed tire.

##RVT797

Don't check your tire air pressure. Really... Stop it.

No, I haven't gone off my rocker as there is some logic behind the title and advice of today's post.

For years the advice has been to check the air in your tires every month and on the RV every morning of every travel day. The primary reason for this decade-old advice has been based on the fact that most RVs have at least one tire in overload or under-inflation or both. Also it is a fact that all tires lose pressure over time and since it is the air pressure that carries the load, not the tire, this makes having sufficient air pressure  more important on RV application than with your regular car.

Why is it more important with your RV?  One major reason is that your car probably has a significant margin in the +12% to +25% range while RVs have more like -5% to +5%, with the plus signifying excess air pressure above the minimum needed to support the load.

But this doesn't explain why I am suggesting you stop checking your air pressure with your hand gauge each morning. The reason for making this surprising suggestion is the fact that the very act of checking your air pressure can, in a small percentage of the times, result in a slow leak through the tire valve core. In some earlier posts on "valves" I showed the sealing surfaces of the valve core and why they can leak. In my experience, valves generally do not develop leaks and are pretty reliable, but the act of checking your air pressure does open the core and there is a possibility that a small piece of grit can be introduced into the core air seal and this grit can cause a slow leak.

Ever wonder why so many people who have a tire sidewall flex failure or "blowout" make the statement, "I just checked the air a couple hours prior to the failure"? Well, this is one of the possible reasons for the small, slow leak.

Now, having made the suggestion that the act of checking your air pressure might possibly cause a tire failure so you might consider not checking your air pressure is only a reasonable suggestion IF you have another method of knowing that your tires are properly inflated. We have that method and it is a Tire Pressure Monitor System.

To me that is the ONLY alternative to checking your air pressure every morning, also every rest stop, also every fuel stop -- and even all those checks will miss a majority of the exposure time when a leak can occur. PLUS, the more times you check your air pressure the greater the opportunity there is for the very act of checking if you have a leak could result in a leak.

BOTTOM LINE
If you have a TPMS you really only need to check its accuracy maybe once a season unless you are getting erratic readings and signals. Using a TPMS will not only make life easier in that you don't have to check the tire pressure multiple times a day, but it will also decrease the likelihood of your actions causing an air leak.

If you don't have a TPMS, then you probably should be checking your air pressure frequently -- but just remember that each time you open the valve with your pressure gauge it may not completely seal shut, with a resultant slow leak.

If this post gets you to finally make the decision to get a TPMS you might read my post on Best TPMS to help you make a good purchasing decision.


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