How much Air Compressor do you need?

 Some things to consider before making a purchase.

When making a purchase decision for air compressor the number one feature to consider is the max pressure capability. You must be able to get up to the max for your tires. You can learn that number by simply reading the sidewall of your tires.

All tires will have a statement that reads something like "65 psi ( 450kPa) air pressure Max load 2,500 lbs (1,135 Kg)". That tire is telling you the MINIMUM pressure needed to support the stated MAX load for that tire.

RV Trailers usually come with Load Range C (50 psi) to LR-E (80 psi) tires. Some large Class-A Motorhomes may say 100psi but there are a few tires that have higher inflation pressure associated with the Max load.
Whatever the highest inflation number on any of your tires, you need to have a bit more capability. I suggest at least +10 Psi with + 30 psi being desirable.
The reason for the extra is that if you need 80 psi in your tire and the compressor is only rated for 80 psi you may never actually get to 80 because the rate of inflation slows down for all compressors as you approach their upper rating.

The second number to look at is the Rate of inflation which will be something like 1.5 CFM (Cubic Feet per Minute) @ 100 psi or maybe 3.0 CFM @ 50 psi. Now you need to pay attention to the "At" number because all compressors will put out more air volume at lower pressure but that 3.0 CFM @ 50 psi unit may only be capable of 0.1 CFM @ 100 psi which means if you are inflating to 105 it might take you a long time ( 20 minutes?). Some compressors, may mislead you with high CFM number but state it at a low inflation number so read the fine print.

Finally do not "over-buy" more capability than you need. If you do you may be wasting money on the purchase and also end up with a physically larger and heavier compressor than you realistically need.

Hopefully you will only need to "top off" a tire by adding 5 psi. If you need to add more than 20% of the goal inflation you may have a problem because if a tire has lost 20% of its air and it was driven there may be damage to the tire structure. Re-inflating a tire that has been damaged could result in a tire explosion. If you need that much air I strongly recommend you call a professional. They should have the training and tools that might even include a "Safety Cage" designed to prevent injury.

##RVT971

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

Do you need your own air compressor? & Certified tire inspectors

Saw an RV forum post on this topic.  Here was my answer.

If you are running a TPMS (which you, of course, should be), you should have received plenty advance notice of needing to add 3 to 5 psi. This slight loss of pressure is due to normal air loss and pressure change due to change in ambient temperature. You can easily top off your tires at your next fuel stop.


If you don't have TPMS and discover you have been driving on a tire that needs more than 20% of it's required inflation, you should be calling road service and have the tire changed, as there is a good chance you may have done permanent internal structural damage. I consider this operation on the under-inflated tire made the tire unsafe to re-inflate until the tire has had a complete internal and external inspection by a trained tire service person, not just the guy that mounts tires who probably has not received the training.

AFTER the inspection, the tire should only be inflated in an approved safety cage as doing otherwise can lead to serious personal injury.


 Regarding how to find trained, certified tire inspectors...  Use THIS link    from Tire Industry Association.


There is a directory that you can search by zip code. Those listed are TIA Members, and those with the Certified Patch next to them have been TIA Certified.

I will suggest that folks with 19.5 or larger tires or with Load Range E, F, G or higher or with any steel body ply of any Load Range go to Certified,  Commercial inspection

People with Passenger, LT or ST type tires of lower load range, can use the "Automotive" link but a certified Commercial person should be able to inspect smaller tires too.

Remember as Sgt. Esterhaus said 'Let's be careful out there'

SAFETY WARNING Sidewall "Blowout"

Having a tire sidewall failure is one thing that can really spoil an RV vacation. What some fail to realize is that there is also the real potential of personal injury if a tire "blows out" when someone is near by.

The Rubber Manufacturers Association has published some guides on the proper way to handle this potential safety issue. I would like to offer part of that information here. My intent is not to scare you but to inform you that working with tires with high inflation levels is not an activity to be taken lightly. There are practices and procedures that need to be considered if or when you are confronted with the need to inflate or re-inflate your tires.

Steel body tires are usually large tires such as 19.5" and 22.5" but some 16" and 17.5" tires also have steel body cord. You should know what is in your tires and this information is molded on the sidewall of all tires. The material - Steel, Nylon or Polyester are used in most tires today. What we are primarily concerned with is the material in the tire sidewall.

Steel body tires can damage their body cord, no matter how low a speed, if the tire sidewall is over-flexed. Over flexing can occur because of over-load or under-inflation or a combination of the two conditions.

According to the RMA "Permanent damage due to operating a tire underinflated and/or overloaded cannot always be detected. Any tire known or suspected of being operated at 80 percent or less of normal operating inflation pressure and/or overloaded could possibly have permanent sidewall structural damage (steel cord fatigue).  Ply cords weakened by underinflation and/or overloading may break one after another, until a rupture occurs in the upper sidewall with accompanying instantaneous air loss and explosive force. This can result in serious injury or death."

In other words, if your normal inflation is 100 psi but you discover you have a tire with 80 psi or less you should NOT re-inflate the tire yourself. If you discover a tire has lost 20% or more of its pressure while being operated you should step away from the tire and contact a service company. All the air should be let out of the tire by removing the valve core.

There are a number of steps that need to be followed. A Safety Inflation cage like this

 is also required. The tire is inflated in steps, with the valve core removed.

I know that many people have posted questions on various RV forums asking about what compressor to use to air up their tires, but I am concerned that few realize the potential danger of inflating a tire that has been damaged. Even with 40 years' experience of inspecting tires I cannot be 100% certain the tire has not been damaged.

The best thing to do if you have any question is to have the tire demounted and inspected by a qualified technician at a tire store that sells the type and size tire you have. Not every tire store has the proper safety cage to inflate high pressure tires.

IMO, having a TPMS is one of the best ways for the RV owner to know if a tire is losing air so the RV can be stopped before the tire has lost significant air pressure and is still driven on.


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Quick posts: Do you need an Air Compressor? Inflation vs Ride comfort?

I recently read a question from a Class-A motorhome owner about the need for carrying your own air compressor. My thoughts and reply to the question:

 If you run the 10% extra pressure (above the minimum required to support the actual tire load) I and others suggest, and if you keep an eye on your pressure every travel day with your TPMS, you should get plenty of warning on when you will need to add air. While +/- a couple psi is normal for temperature variation, if you see a 5% loss one day and another couple the next, etc., then that should be a warning that you have a leak, which indicates some problem that needs to be addressed sooner rather than later. Once you see -5%, simply stop at the next fuel stop and use the high pressure that is available at truck stops.

People need to remember that it is normal for tires to lose between 1% and 2% of their inflation pressure each month (adjusting for temperature and barometric pressure variation). This is the result of the molecules of air moving out between the spaces between rubber molecules. I also note the concern about most small compressors not being able to inflate a large tire that has lost a lot of air.

If you have lost sufficient air to be more than 10% below what is needed to support the load, you really do have a problem that more than likely needs professional service, not simply a "top off" of air. If you have lost 20%  or more, you should not be driving on that tire and also should not be inflating your tire outside a service center tire safety cage, as running a tire very low may have damaged the steel body cords to the point that the tire might explode when being inflated and result in injury.

====================
I also read a question about running the exact air pressure needed to support the tire load. Following this practice creates a couple problems:

1. Every time the temperature changes 10°F, your pressure will also change about 2%, which could mean you would be running your tires under-inflated. Not a real big deal, but every mile of operation in overload may consume part of the tire life with the potential of having an early failure.

2. I believe that you would soon tire of constantly adjusting your tire pressure up or down one or two psi every day. When you get tired of this constant effort, I am afraid there may be a tendency to forgo checking and adjusting the air. This could lead to a failure when you go an extended time without checking your pressure. This is why I suggest the 10% margin.

Of course this raises the question from some about increased inflation causing hard ride. Now, running higher pressure could lead to a harder ride, but while I believe that running more air than the minimum needed to support the load may theoretically contribute to a harsher ride, I doubt that there are many riding in Class-A RVs who can feel a 5 psi or maybe even a 10 psi difference in a controlled blind test. This 5% or 10% translates to a 1 to 3 psi difference in a car, and I have seen many people unable to notice changes of 5 to 15 psi (20% to 50%) in passenger car operation.

See my post about not getting your "shorts in a bunch" about air pressure.



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Do you need a portable air compressor

A number of people have wondered if they need to carry their own air compressor so they can maintain the pressure in their tires. While keeping the correct level of pressure in your tires is important for the safe operation of your RV, I believe there are a few preventative measures that can be takes so you can avoid the need to carry around a compressor.

There are a number of things to consider before you go out and spend $20, $100 or even $300 when it may not be necessary to have a compressor for normal inflation maintenance.

First, lets lay out a plan on how to manage inflation without owning a compressor. We are going to assume you are not trying to inflate a tire that has gone flat due to a puncture or faulty valve. If your tire has gone flat and the tire bead detached from the rim you need not only high pressure but high air volume which a small compressor simply cannot provide. There are also safety concerns when it comes to inflating a flat tire. This task should be left to the professionals.
Since most tires will loose about 1% to 3% air pressure every month due to permeation through the rubber and you might also see a pressure loss of 1% to 3% due to a significant drop in ambient air temperature, there is the potential of needing to replace 5% to 6% of your air every now and then. This translates to a pressure loss of 2 to 7psi which is not a large amount but could be enough to be under your minimum pressure if you haven't set your pressure with sufficient safety margin.

I suggest that motorhomes set their cold inflation for all tires on a given axle at the minimum needed to carry the actual load on the heaviest tire on that axle PLUS at least 10%. If you have a TPMS you will quickly learn your "normal" weekly or monthly air pressure drop so as you travel you will have advance warning of when you need to "Top-off" your tire pressure. With this knowledge you can get air when you stop for fuel. Even the largest Class-A will be able to get enough pressure at the truck stops when they fill-up and smaller Class-C or Class-B can replenish the 5% pressure loss at the regular gas station.

If you are going to be parked at one location for more than a couple of weeks I would suggest one of the last things you do before getting to the campground would be to inflate your tires to the tire sidewall max pressure. This way even after a month or two you should still have enough pressure to still be above your minimum cold inflation when you leave the campground and you should stop at the first location where you can get air to replenish the inflation to your 10% cushion.

Trailers have a different problem given that I recommend they always run the tire sidewall max. The good news for trailer owners is that they have smaller tires so even a small 12 volt compressor should be able to top-off their tires. I would just spread out the task over a few hours the day before planned travel, so as to not overheat the compressor.

If you decide you still want a mini-compressor so you can add 2 to 5 psi to your tires, I would plan on spending at least $50. One thing to consider is to get a compressor rated at least 20 psi higher than the max you need. You also need to look for "duty cycle" rating. This is the % time you can run the compressor without overheating the unit. You don't want a unit that can only run for a few minutes before it must be shut down to cool. The ultra low cost compressors I have looked at seem to get very hot. This could be because the "cooling fins" are simply molded plastic rather than heat conducting metal.

If you have access to 120 volts at your campground or with an on-board generator I think you can find a small compressor for less than $50 that can meet your pressure needs if you feel you want to be able to top off your tires and not depend on truck stop or gas stations for air pressure.


Safety note You should never exceed the max inflation rating of your wheels or valves when establishing your "cold" inflation level, Some wheels may be marked but it seems that most of you will need to contact your RV manufacturer or wheel manufacturer to get the specification, in writing. I would not accept the simple "match the tire inflation" as the answer. Wheel manufacturers have a specific number and do not depend on the tire pressure as they cannot be sure what tire is going to be mounted on their wheel.
Also I would not use basic passenger tire "snap-in" rubber valves in RV application. You can review the posts on valves for more detailed information.

How to "Top Off" your inflation pressure

Hopefully all the readers of this blog understand the importance of having the correct inflation pressure in ALL their tires. Be they on a 45' Class-A, your toad, a tow-dolly, regular passenger car or anything in between. The question is how do you get a few more psi of air for your tires when you check in the morning.

There are a number of different situations and I can't possibly address them all here, but I think you can review these suggestions and find a plan that will work for your situation.

I do need to separate out the few folks that discover they have a flat tire or one that has lost more than 20% of the minimum required pressure. NOTE: Tires that have lost 20% of their air are considered "flat" by the tire industry. You have a problem. Maybe a puncture or a failed valve or a tire that has been damaged. You should not drive on your flat tire. You need to change it if you have a spare and the proper tools and experience to do the job safely, or have it changed by a tire service truck and technician.

Now the rest of you who just need a few psi to get back to your goal inflation that provides the inflation needed to carry the load plus a few psi "cushion", there is a way to handle your situation. The options depend on how much air pressure you need.

If you need 80 psi or less one option is to carry a small "tankless" or "pancake" compressor rated at 100 psi and 1 or 2 Cubic Feet per minute (CFM). These are available for $20 to $60 at discount tool supply companies or auto parts stores. Some are 120V and some are 12v and can run off your battery or on-board generator. Just be sure you have enough extension cord or air host to get to all your tires.

NOTE You will have a tough time ever inflating a tire to the pressure the compressor is "rated" for so don't buy a 100 psi compressor is you need 100 psi.

If you have a larger rig like a Class-A, you probably need 90 to 120 psi and a compressor rated at 125 to 150 psi and 2 CFM or higher. If you have air brakes you may have enough on-board capacity and just need the appropriate fittings and host. There are small compressors on sale at less than $100 that claim to be capable of 125 psi.

One other option for those only a few psi low. Drive to the nearest service station at slightly reduced speed (10 mph under the speed limit would be max) and follow these instructions on how to inflate a hot tire.

1. Record your cold inflation.
2. Calculate how many psi each tire would need to reach your goal cold inflation.
3. Drive at reduced speed, hopefully no more than 10 miles, to the service station with air available. You might want to call ahead to be sure they have enough space or long enough hose to reach your rig. Not all service stations can accommodate a Class-A with a toad.
4. Measure your now warm inflation pressure
5. Add the psi needed from step #2 above plus 3psi to learn your temporary "warm" tire inflation
6. Inflate your warm tires to the temporary goal inflation calculated in step 5.
7. Confirm you have the needed inflation the next morning after the tires are at ambient temperature and adjust accordingly.

If you follow these steps I think you will find that your tires have the proper inflation or 1 or 2 psi more so you can set the inflation at your exact goal cold inflation using your digital gauge.

If you have any concerns then have a service truck come out to top off your tires.
Remember DO NOT DRIVE on any tire that has lost 20% or more of its air.

How to get dry air for your tires

A good part of the discussion on the advantages of inflating tires with Nitrogen focuses on stable inflation pressure which seems to be of concern to some. Now for race car application this is important and the benefits are meaningful in that application but I do not think that a fluctuation of a few psi due to temperature variation is meaningful in normal highway use. Measurable but not meaningful.

I can accept the fact that no matter what my opinion is, some will still argue that stable tire pressure is desirable, so they feel the expense and complications of using Nitrogen are worth the cost. While there are some theoretical advantages to inflating tires with a gas that is low on oxygen, I don't think they are worth the effort. I have both Argon and a mix of Argon and CO2 available to me in my shop but I still use regular air from my compressor. The one thing I do have with the air in my compressor is the knowledge that the moisture level is low, as I have filters and water separators in my system.

But what do you do if you don't have a well equipped shop in your back yard but still want dry air? I am going to show you a set-up I have, that costs about $20 and can be used to inflate your tires for years to come.

Above is a small air drier system I use in my shop for some special equipment that needs especially dry air, you can duplicate it to ensure the air you are using to inflate your tires is dry.

The dryer is available at 2/$20 at WW Grainger as well as $8 ea at Advance Auto. Be sure the one you buy is rated for the air pressure you need. Harbor Freight units are rated only 95 psi.

•The air chuck is under $2 at Harbor freight
•Quick connector set is $5 a set or less at Harbor freight.

Note my four year old desiccant is purple not blue so I am getting close to needing to change the dryer which is a disposable unit. To help keep your dryer from getting old fast, keep it tightly sealed in a good zip-lock bag or some container with air tight top as I do.

There are too many individual air setups for me to identify all the possibilities but this simple dryer will deliver what you need.

Warning. If you are going to try and "dry out" the air in your tires by changing your "wet" air you need to jack up the tire so it is not contacting the ground. If you let air out don't go too low or you may have problems with losing the seal at the bead. A quick test to see if you have lots of moisture in your inflation air is to remove the valve core. If water spits out you have excess moisture in the tire. You may even need a tire store to service it to get the excess moisture out.

Hope this will save money for those wanting dryer air in their tires.