Choosing The Best Portable Air Compressor For Car Tires
(Camp Addict does NOT accept payment from any company to review or endorse their products.)
Proper inflation your car, truck, or RV tires is something every driver must take very seriously.
Don't be that person driving down the road with an overloaded vehicle and tire sidewalls bulging because of severe under-inflation.
Choosing the best portable air compressor for RV tires, car tires, or truck tires means having the right tool in your home garage to ensure your safety when the rubber hits the pavement.
Here, you'll find everything you should know to choose the best portable air compressor for RV tires, car tires, or light truck tires.
You will also become 'fluent' in all things about portable air compressors as well as learn why you need to care about air pressure level in the first place.
Let's get started.
Looking for a new 12-volt air compressor? Click the button below to read the best portable air compressor reviews.
Portable Air Compressor Guide
Here you'll learn about why proper air inflation is important, how to determine how much air goes into your tires, and what features to look for when shopping for the best portable air compressors.
It's not all dry, boring stuff (OK, maybe it is), but it's verrrrry important.
It's important information. Best that you have a basic understanding of it.
Your tires, and possibly your life, will thank you.
Importance Of A Properly Inflated Tire
So what's the big deal about tire air pressure? Why should you care?
I mean, aren't these tire thingies made of solid rubber? Oh, you mean they have actual air in them?!?!?
Ok, we're pretty sure you know auto and RV tires have air in them. You probably DON'T understand how important it is to monitor them and maintain the correct pressure.
If you do, congratulations! You are way ahead of most knuckleheads.
Alright, so why exactly do you need to care how much air is in your tires? In other words, why is air pressure so dang important?
Because first off, all tires carry a certain load on them.
The load consists of the weight of the car the tires support.
Any given tire can support its maximum load rating depending on the pressure inside of it.
Generally, the higher the pressure, the greater the load a tire can support. (ALWAYS follow the recommended tire pressure as provided by the auto manufacturer.)
Besides the load-carrying capability of a tire, air pressure affects the following:
- Tread wear - over/under inflated tires don't wear evenly
- Sidewall life - under inflated tires cause excessive heat buildup in the sidewalls, causing them to prematurely fail
- Fuel economy - under inflated tires have higher rotational friction, which burns more gas
- Road damage - correct inflation ensures that the tire can stand the impact of road hazards (debris, potholes, etc)
How Often Should You Check Tire Pressure?
The general rule of thumb is to check your tire pressure at least once a month. We know this sounds like a lot, but his is the bare minimum!
However, it is MUCH smarter to check the pressure before the start of every trip.
All new passenger vehicles sold in the United States as of 2008 have a tire pressure monitoring system (TPMS) that alerts the driver when a low pressure situation is present.
While this is a great safety device, it isn't a replacement for physically checking your tire pressure. TPMS systems will not alert you if there is an over-inflation situation or if a tire is slightly underinflated.
They only alert you once a tire is severely underinflated.
RVs generally do not come equipped with tire pressure monitoring systems (good luck finding a travel trailer that comes equipped with a TPMS from the factory).
There are aftermarket systems you can install (and you should!), but again, even if you have a TPMS system installed on your RV, you should regularly physically check the pressure on ALL of your tires.
It's a PITA, but it's better than having an expensive and potentially damaging or even fatal blowout!
Tire Pressure Gauge
Yes, we've established why you should keep tabs on your vehicle's tire pressure regularly. But does this mean you need to lug out your portable air compressor pump to use its built-in pressure gauge just to check pressure?
Heck no! What a pain that would be!
Instead, get an inexpensive, yet accurate, pressure gauge like the Accutire MS-4021B Digital Tire Pressure Gauge shown below.
This particular gauge is the one that Camp Addict Co-Founder Marshall has been using for longer than he can remember.
According to Marshall, 'do yourself a favor' and pick up the air pressure gauge below.
It is very inexpensive, easy to use, easy to read, and should be in every vehicle's glove box.
Portable Air Compressor Terminology
There are a lot of options when it comes to small portable air compressors, but not all are created equal.
During your quest to find the best portable air compressor for car tires, you need to know what you are looking for and what features to compare.
Below are some of the air compressor terms to be aware of. (Beware- dry reading coming up!!)
Duty cycle is the amount of time in one hour that a portable tire inflator can be run nonstop. After that, it needs to be 'rested' to cool off.
For example, if the duty cycle is 25 minutes, the portable air compressor pump can be run for 25 minutes out of 60 minutes. It should then be 'rested' for the remaining 35 minutes.
This ensures that the car air compressor and pump motor don't overheat (though the best portable air compressors have thermal overload protection to prevent motor damage due to overheating).
Duty cycle can also be represented by a percentage, so a 33% duty cycle would be 1/3 of an hour or 20 minutes.
Therefore, a 33% duty cycle portable air compressor pump can be run continuously for 20 minutes before needing to be 'rested' for the next 40 minutes.
Duty Cycle Considerations
A small air compressor for tires is going to have a specified duty cycle rating. It tells you how long you can continuously operate it before it needs to 'rest' (cooldown).
Two things to consider:
1) The reason a duty cycle exists is heat. The compression of air creates heat. Therefore, the compressor itself can withstand a certain amount of heat.
An air compressor cannot run all day. It will overheat. A quality portable air compressor protects itself. It cannot be damaged by overheating.
Some of the Viair compressors that we review have a thermal protector. This feature automatically resets itself. Therefore, if you run it too long (exceed duty cycle, or operate in high heat), this protection will automatically kick in once it reaches a high enough internal temperature.
2) You Likely Won't Use The Air Compressor Non-Stop. Using a 33% duty cycle (20 minutes out of every hour) as an example, you are probably not going to run a portable air pump for 20 minutes non-stop. Of course, a quality portable air compressor pump doesn't take 20 minutes to fill up a single tire.
Therefore, you aren't going to be continually running the car air compressor as you fill up all the tires that need air. You will be 'pausing' as you check the pressure and move the air chuck from one tire valve to another.
You can certainly get a 100% duty cycle portable air compressor pump. Meaning it doesn't have to cool for a certain number of minutes each hour.
These air compressors achieve a long duty cycle by having a lower output (CFM - see below) than their counterparts with a lower duty cycle.
The lower output means the air compressor pump isn't working as hard, thus not generating much heat.
The portable air compressor duty cycle is based upon a certain outside temperature. Viair air compressor's have a duty cycle rating based upon 72º F.
Temperatures higher than this may cause the compressors duty cycle to be lowered as the unit may take longer to cool off (and heat up quicker in the higher outside temps).
Cubic Feet per Minute (CFM)
Cubic Feet per Minute is the measure of how much air a portable air pump for cars is able to send to the tire it's inflating.
In other words, how much air the compressor pump is able to send down the air hose to be used to fill up tires.
The larger the CFM rating a portable air compressor pump has, the quicker it is able to inflate your tires. However, a compressor with a higher CFM rating will be larger, which requires more power from your auto.
Looking for a new 12-volt air compressor? Click the button below to read reviews of the best portable air compressors.
This isn't necessarily a bad thing. It's just that a more powerful portable air compressor pump (higher CFM) needs to be connected directly to your car's battery. This is because a 12-volt outlet won't be able to supply the necessary power.
An air compressor pump will have a different CFM rating depending on the air pressure it is 'pressing' against.
For example, if a tire is completely flat (0 PSI), a compressor has zero resistance to 'press' against and can have a higher output.
Makes total sense, right?
Therefore, an air compressor pump has its highest CFM rating at 0 PSI.
Gradually, as the pressure inside the tire increases, the air compressor pump has to work harder to put more air in. Because of this, its CFM rating decreases as the pressure increases.
As an example, the Viair 400P Automatic has a 2.30 CFM rating at 0 PSI but drops down to 1.54 CFM at 60 PSI.
Compressor Comparisons
A small air compressor for tires with a 100% duty cycle will have a lower Cubic Foot per Minute rating than a similarly sized air compressor with a lower duty cycle (such as 33%).
This is because the compressor pump with the 100% duty cycle is designed to be run longer without resting so it can't be working as hard.
The more a compressor 'works' the more heat it produces. Consequently, a long duty cycle requires a cooler running air compressor.
Viair Explains Cubic Feet per Minute (CFM)
Automatic Air Compressor
Viair has a couple of automatic portable air compressor models. But what in the heck does automatic mean?
It means that the compressor pump can turn itself off automatically (without you having to turn it off) when you pause filling up a tire.
This is usually done by releasing the trigger of an inflation 'gun'. Being able to 'pause' an air compressor serves two purposes:
- You can move from one tire to another without having to shut off the compressor. Many (including some Viair models reviewed) portable compressors require you to turn them off before you disconnect the air chuck from the tire valve to move it to the next one.
- It allows you to get an accurate pressure reading. With a typical tire inflator, the built-in pressure gauge isn't accurate when the pump is actively putting air into the tires.
To read the pressure, you need to switch off the pump, take the pressure reading, and turn the pump back on if more air is necessary. (eew)
Viair automatic air compressors let you keep the compressor turned on and still can get an accurate pressure reading.
You simply release the trigger of the air inflation gun to stop air from flowing into the tire, look at the built-in gauge on the inflation gun, and then press the trigger again to continue filling up if needed.
Simple! And no rushing back to the compressor to turn it off in order to read the air pressure.
This ability of the air compressor to turn itself off when you aren't 'asking' it to actively fill a tire also allows you to move from one tire to another without having to physically flip the power switch to the 'off' position, then back 'on' when you have attached the air chuck to the next tire valve.
What Pressure Should Your Tires Be Inflated To?
Since the whole purpose of a portable air compressor for car tires is to get air into your tires, it's a good idea to understand how much air to put into them.
The amount of air inside a tire is expressed in PSI (pounds per square inch) or kPa (Kilopascal - common in Europe). This is the unit of measure used to express how 'full' of air a car tire needs to be.
A tire pressure gauge measures the PSI or kPa reading.
Check Pressure When Tires Are Cold
Check the pressure when the tires are cold (before you drive the vehicle for the day).
The recommended pressure is based upon a cold tire PSI or kPa reading. As you drive, road friction heats the tire, which in turn heats the air inside it. As the air heats, the car tire pressure increases (slightly).
Tire pressures given by auto manufacturers factor in this heat buildup as the tires go down the road. Checking cold pressure ensures the operating pressure is what the car manufacturer intended it to be.
OK great, tire inflation pressure is measured in PSI or kPa, but that still doesn't answer the question!
What pressure should your vehicle's tires be inflated to? Well, like many things in life, 'it depends'. (sigh)
Fortunately your vehicle manufacturer normally tells you what PSI/kPa to inflate the tires. Therefore, it's simply a matter of finding out where this information is.
Generally, all car, trucks, and SUVs have a tire data placard inside one of the door jambs.
Front and rear car or truck tires may have different pressures. RV's have a similar data placard somewhere on the outside of the rig.
Vehicle Tire Placard Example (33 PSI cold)
RV Tire Placard Example (50 PSI cold)
Portable Air Compressor Features To Consider
- Power cord and air hose length - You need to have a power cord that's long enough to reach the power source and have the air compressor sitting safely outside. Also, you need to have an air hose that reaches from the air compressor to your tire valve with ease.
- Power cord and air hose quality - a cheap air hose and/or power cord will fail after being used a while. Look for a portable tire inflator that has an air hose that stands up over time. You need a power cord that not only is heavy enough gauge wire to handle the power load, but also has quality electrical connections.
- Gauge legibility - most (all that you'd want to consider) portable air compressors come with an air pressure gauge. But you need to be able to read it or it doesn't do you any good. Make sure the gauge has graduations small enough so you can truly read the exact pressure. If you cannot tell if the gauge is reading 30 PSI or 35 PSI because there are no markings, it's useless.
- Gauge accuracy - the built-in pressure gauge doesn't do much good if it doesn't accurately indicate the pressure. You want a gauge that reads within a very small percentage of the actual pressure or spot on. An LCD display makes reading the pressure very easy.
- LED lights - an LED flashlight illuminates the area so you can see in the dark. This feature is debatable. If you don't have a built-in LED light, use your phone's light.
- Duty cycle (run time) - how long you can run a car air compressor before it has to be rested in order to cool off.
- Output (CFM) - how much air the compressor pump is capable of outputting in a minute, which indicates how quickly it inflates a car tire.
- Thermal Protection - air compressors get hot when they run. Under certain circumstances they get too hot to function properly. This is why a compressor has a duty cycle. The best portable air compressors have thermal protection, which shuts down before getting too hot. This prevents overheating damage.
- Automatic compressor - the ability of an air compressor to turn itself off when you release the trigger of the air inflation gun.
- Inflation speed - how quickly a portable tire inflator fills a tire from a totally flat condition or from a partially inflated to fully inflated condition. Inflation speed is a direct result of the air compressor pump output.
- Storage bag - Gives you a place to centrally store your compressor, air hose, air fittings and other accessories. All Viair compressors reviewed include a carry bag.
- Overall quality (body, feet, gauge, air hose, power cord, etc) - there are a lot of portable tire inflators on the market. This includes a lot of very poorly built air compressors. Unless you like to buy a new portable air compressor on a semi-regularly basis, look for one that is built with quality components.
Looking for a new 12-volt air compressor? Click the button below to read the best portable air compressor reviews.
Tire Inflator vs. Portable Air Compressor
Let's just get this out - technically ALL devices that inflate tires are 'tire inflators'. But there is a real difference in what we are talking about.
We are referring to the different styles of 12-volt devices that put air into car tires.
In this case we are referring to the style of devices (tire inflator versus air compressor), not what they do (put air in tires, or inflate tires).
Got it? Good!
Now that we are (crystal?) clear on what we are talking about in this section, let's get to it!
The items we reviewed on this page are portable air compressors, so they fall into the 'air compressor' column. The other style of doohickey (or is it a whatchamacallit?) are tire inflators.
What's the difference??? AND why are only portable air compressors reviewed on this page if a tire inflator will, well, inflate a tire?
We'll make this simple - tire inflators are fine if you have lots of time on your hands. You must enjoy hearing a small, not very powerful air compressor pump go on and on and on. Good for you!
Sure, even the best portable tire inflators have very small compressors and can take forever to fill up a deflated car tire.
In other words, why would you want to use a portable tire inflator when there are MUCH better options (12-volt portable air compressors)?
What Size Are My Tires?
Portable air compressors are rated to fill tires up to a specific size (diameter).
This is because a larger diameter tire contains more air. More air room requires a compressor with a larger air output in order to fill it up in a reasonable amount of time.
You need to match the air compressor output with the largest tire you will be inflating. Then, you don't spend half your day waiting around for it to finish.
There are two ways to find out how large your tire is (what diameter it is).
You will want to do this with the largest tire you will be inflating (Ex, if you have a large RV tire you want to inflate, measure that one).
This means your portable tire inflator will not only be capable of inflating smaller auto tires, but it will have the capacity to inflate the largest truck tire you have.
Two Sizing Methods
There are two methods of figuring out tire diameter.
Measure using a tape measure or enter your tire's specifications into an online calculator and let it tell you the diameter.
Direct measure diameter - Using a tape measure, go up to the largest tire you will be inflating and measure it. Easy? Yup!
But you need to measure it correctly.
Measure the diameter by holding the tape measure vertically at the center of the wheel assembly. Make sure the end (the 'zero' point) is on the ground and then read the diameter at the top of the tire.
See the picture below for a visual reference. The tire in the picture below is 30 inches in diameter.
Hold Tape Measure Vertically at Center of Wheel
Online calculator - To use an online calculator to figure out diameter, you need to know the specifications of the tire itself. These specs are presented in the following format:
'LT265/60R18'
You can read this directly from the tire itself (choose the largest one you will be inflating).
If your car, truck or RV has the original size tires still installed, you can also find tire size information on the data plate. They are usually located on the door jamb of your vehicle or on the side of your RV.
Travel Trailer Tire Size Example (205/75R14)
Truck Tire Size Example (265/60R18)
RV Tire Placard Example (205/75R14)
Vehicle Tire Placard Example (265/60R18)
The letters at the front of the specs (P, LT, ST, etc) indicate what type of use the tire is designed for. You can ignore this as you are only interested in the numbers.
The numbers designate certain measurements of the tire, which we won't go into here.
If you are interested in knowing exactly what these numbers mean, Goodyear has a good explanation of this.
Once you've located your specifications, you can 'plug' this information into this online calculator (three blank boxes in the left column titled 'Tire Calculator').
Once you've entered the correct information into the three boxes and click the 'calculate' button, the diameter is displayed.
Press-On Chuck Or Twist-On Air Chuck?
First off, what in the heck is a 'chuck'?
It's not that guy that was the superstar athlete in high school who is now the night manager at the local burger joint. Heh.
An air chuck is the part of a portable tire inflator that attaches to your car's tire (specifically the valve stem).
A tire chuck can come in two 'flavors' - a twist-on (or screw-on) style and a press-on style.
Twist-On (top) vs Press-On (bottom)
With a screw-on (twist-on) tire chuck you have to physically twist (or thread) the chuck's female threads onto the valve stem's male threads.
This makes for a very secure, leak-resistant connection. However, it is slightly slower than the press-on style to screw and unscrew from the valve stem.
A press-on air chuck utilizes a quick-connection system that fits over the top of the tire valve stem. You then flip down a lever that secures the connection.
This is definitely quicker. That said, it may be susceptible to debris getting inside the chuck and degrading the sealing capability over time.
Here's a quick breakdown of the pro's and con's of each style of air chuck:
Screw-On Air Chuck
Press-On Air Chuck
So, which style is right for you?
'It depends'. Don't you 'love' that answer?!? (RRRRRRR)
Let's help you decide. If you are an off-roader that uses your portable air compressor in harsher environments where there is the possibility of sand/dirt getting into the chuck body, go with a twist-on style.
These are easier to remove debris from as you can just blow out the threads, do a quick visual check to make sure things are clear, and get back to it.
Whereas a press-on chuck's interior material is more susceptible to damage from said debris. Also, it is harder to tell if it's free and clear inside.
However, if your vehicle(s) rarely leave pavement and you aren't using your portable tire inflator in the dirt, then the press-on style may be the way to go.
As long as you keep the inside of the chuck free of debris, it should give you years of trouble-free service.
I (Camp Addict co-founder Marshall) have been using a portable air compressor with a press-on chuck for close to 15 years (the same compressor). It still works great.
Then again, I'm not a hard-core off-roader dragging it through the dirt and I tend to take care of my equipment.
Choose which style of air chuck you think works best for you and then use your compressor!
Don't think too hard about it. Both do the job, both will be fine if you take care of them.
12-Volt Outlet Or Direct Clamp To Battery?
If you are shopping for a portable air compressor for your car or truck or RV, there is one VERY important item you need to consider before you decide.
How will you provide power to your air compressor?
The name '12-volt air compressor' implies that a 12-volt power source is required. Your auto has a 12-volt electrical system and thus can provide the needed 12-volts of power.
But it isn't that simple.
There are two ways to get the needed power to your portable air compressor:
- 12-volt (cigarette lighter socket) outlet
- By directly clamping the power leads to your car battery.
12-Volt Outlet
This is the round-style electrical plug (cigarette lighter socket) that you can use to power various low-power consuming appliances.
The Viair compressors we review that use a round power connector that plugs into a 12-volt outlet require an outlet rated for at least 15 amps or 180 watts.
This is a large amount of power. Many 12-volt outlets cannot provide this much power.
Typical 12-Volt Power Outlet
How do you know how many amps your 12-volt power outlet (cigarette lighter socket) is rated for?
The power rating is either noted at the outlet itself (on the outlet door or above/below the outlet opening) or it is indicated in the owner's manual.
Owner's Manual Indicating 13 Amp 12-Volt Outlet
What happens if you try to plug in a portable air compressor into a cigarette lighter socket that isn't capable of handling the compressor's electrical load?
Best case scenario is that the fuse that protects the power outlet blows and you have to replace said fuse.
Worse case scenario (and this would only happen if the power outlet was wired improperly without a fuse protecting it) is that the outlet wiring would get too hot, potentially melt, or even start an electrical fire.
Yeah, it's kinda important that you don't 'ask' too much of a cigarette lighter socket by plugging in something that requires more amperage than the outlet is capable of supplying.
If you are unable to determine the maximum number of amps your 12-volt cigarette lighter socket is capable of providing, go with a portable air compressor with a car battery clamp power cord.
Looking for a new 12-volt air compressor? Click the button below to read reviews of the best portable air compressors.
Direct Clamp To Car Battery
If your car doesn't have an outlet capable of providing the amount of amperage that the portable air compressor for car tires requires (minimum 15 amps for Viair compressors equipped with a 12-volt 'plug' reviewed on this page), then you need to get an air compressor with power cords that directly clamp to your car's battery.
This allows the car air compressor to pull as many amps as it needs directly from the battery. No worrying about any power outlet fuses blowing.
This style of portable air compressor has an inline fuse on the positive cable.
The fuse protects the air compressor (and wiring) from too high of amperage draw since the car itself isn't providing the protection via built-in fuses.
Battery Clamps
Power Cords Connecting Directly to Battery
You need to be able to access your auto's battery in order to clamp the air compressor power cord to it. You also have to be confident in connecting/clamping to the battery.
Just make sure the air compressor power switch in the 'off' position before connecting the power cord.
Also, in order to reduce sparking potential, it's smart to connect the negative (black) power cord clamp to last and remove it first when disconnecting.
Conclusion
You should now have a better understanding of portable air compressors and understand why it's important to keep an eye on air pressure.
Your auto tires are one of the most important parts of your car, truck, or RV, when it comes to safety. Having them properly inflated is just one basic part of auto maintenance that you should keep up with.
If you have a portable air compressor in your home garage, then you are able to easily maintain proper car tire pressure, no matter where you are. It's an essential tool that every one should have.
To be really prepared, keep a tire inflator in your car trunk in case you have an emergency while driving.
Happy motoring and here's to many years of healthy car tire life!
Authors: Kelly Beasley & Marshall Wendler
Kelly Beasley
He-llllo. I'm the co-founder of Camp Addict, which my biz partner and I launched in 2017. I frigging love the RVing lifestyle but in December of 2020, I converted to part-time RV life. Heck, I lived in my travel trailer for over 5.5 years, STRICTLY boondocking for pretty much all of it. Boondocking is a GREAT way to live, but it's not easy. Anyway, I'm passionate about animals, can't stand campgrounds, I hardly ever cook, and I love a good dance party. Currently, I can be found plotting and scheming whether or not to start collecting farm animals (or plotting my next RV trip!) at my beautiful new 'ranch' named 'Hotel Kellyfornia', in Southern Arizona.
Marshall Wendler
Camp Addict co-founder Marshall Wendler brings his technical expertise to help explain RV products in an easy to understand fashion. Full-time RVing from April 2014 - December 2020 (now RVing about 50% of the time), Marshall loves sharing his knowledge of the RV lifestyle. Marshall spends the majority of his RVing life boondocking. He is the part of Camp Addict that knows 'all the things'. He's good at sharing his technical knowledge so you can benefit.
What is the correct tire pressure? If you are working with a heavy load, it is most likely NOT the one printed in your door frame. Car manufacturers typically assume some ‘medium’ load when specifying the tire pressure (it says the load used on the sticker).
The correct tire pressure is obtained by the ‘load inflation table’ produced for the specific tire by the tire manufacturer. Get it directly from the tire manufacturer. The tire stores are unlikely to be helpful. Vehicle manufacturers, although they must have had this information to prepare the door sticker, will not be helpful in finding anything other than what is printed in the door frame. If your tires are different than the ones the car was built with (likely), the correct tire manufacturer needs to be consulted.
To use the load inflations table, find your tire size and the load on each tire to determine the inflation pressure. Typically both tires on the same axle will be close enough that the axle weight divided in half is adequate but front and rear axle weights will most certainly be different enough to produce different pressures. With the tire load, you can find the correct tire inflation pressure. The correct tire load must include the RV/load at ‘wet’ (full fuel/water/personal goods etc) condition. If you use a trailer load weight distribution hitch, it must be installed.
Continuous duty vs intermittent duty;
Your statements infer that continuous duty compressors are ‘smaller’ and that intermittent duty compressors are ‘larger’. While this seems true, it is really a matter of ‘specs-manship’ played by manufacturers. A given compressor may be ‘rated’ (and possibly controlled) slightly differently to produce two differently appearing products.
By definition, a ‘continuous duty’ product can BE CONTROLLED to operate at a lower capacity so its heat generation can be safely dissipated. The same compressor can be classified as an ‘intermittent duty’ product by allowing it to operate at a (higher) capacity where it cannot safely dissipate all the heat and will eventually overheat if operated long enough.
The game being played is the manufacturer HOPES your tire(s) becomes full before the compressor overheats. This assumes the compressor is correct for the tire, the conditions are friendly and if it does overheat, it doesn’t happen long or often.
This may be a good bet if you only used it to ‘top off’ a tire or two but if you use it a lot, such as to reinflate all tires after operating off-road, you will likely experience compressor failure early due to frequent and excessive overheating. The message is, if you only partially fill one or two tires, an intermittent-duty compressor will likely be fine. If you make big changes in air pressure in multiple tires, you really need a continuous-duty compressor.
Thanks for the comment, Steve!
I looked over the duty cycle section of this page, and I don’t see where I’m inferring that there is a size difference. Maybe I am not looking at the same spot that you are referring to?
Both Kelly and I have the Viair 400P-RV Automatic, which has a duty-cycle of 33%. On multiple occasions, we have aired down truck tires to go offroading (mainly at altitude in Colorado). At the end of the ‘adventures,’ we have successfully aired up four tires with the limited duty-cycle Viair without having an issue with the compressor overheating (the thermal protection never ‘kicked in’).
So far, the Viairs have been motoring right along after many years of use. Keep in mind that we don’t offroad that much. Don’t enjoy being bounced around for hours at a time. So we are hardly the poster children for abusing the Viairs. Just wanted to point this out so that if someone wants to occassionally air up tires after going offroad, a 33% duty-cycle Viair will most likely work for them.
If one was a more hardcore off-roader, they’d want a compressor with a 100% duty-cycle just to make sure it lives a long and happy life.
I read with interest your article on air compressors. I noted your cold pressure check information. I’ve reached out to multiple organizations on the question of tire pressure. Here is the scenario: You start out in a mountain campground. Temperature is a typical 60 degrees. You inflate to the recommended 80 psi. You head down the mountains to a desert environment. The temperature is now 90+. In addition to the temp rise do road travel. The TPMS now reads 95 psi and rising. True life situation. You are now 15 psi over max. What’s an RV’er to do? The reverse could also happen. Hot to cold and under inflation.
Hey Steve,
Thanks for the comment and for visiting Camp Addict!
Great question! And one that we deal with fairly often. In fact, just a few days ago I made the 2-day (2 really long days!) trek from Salida, Colorado (I was at around 8,000 feet and in the 60’s) to Tucson, Arizona (at 1,900 feet and in the 90’s).
I’ve never seen anything definitive on this, so I’ll tell you what I do.
I air up to the correct (cold) pressures before I leave. Doing this first thing in the morning before the sun has had time to heat up the tires.
I make the drive.
I check/adjust the tire pressures the next morning after reaching my destination (or, heck, you could do it at the mid-way stop if you have one), again before the sun has had time to heat up the tires.
There is really nothing you can do otherwise in this scenario. Sure, you can deflate the tires as you come down, but who does that?
Let’s talk about what happens when a tire is overinflated. Assuming that the tire pressure never goes above the recommended maximum tire pressure ‘stamped’ on the sidewalls. And speaking from experience, both on my tow vehicle and the trailer itself, I never inflate tires to anywhere close to the max pressure. I inflate it to what they are supposed to be inflated to (which always comes under the max pressure).
Back to overinflated tires… An overinflated tire will have a crown on the tread. This causes uneven wear on the middle (top of the crown) of the tire.
In the long run, this is an issue. In the short term (one day of travel), this isn’t going to do anything measurable (not that I’ve ever measured, but I don’t see how a few hundred miles is going to do in your tires when they are inflated too much).
So as long as you adjust your tire pressures to what they should be when you arrive at the lower elevation, you should be fine.
Side note: Not only is the increased temperature a factor but so is atmospheric pressure. When you descend, the outside air pressure goes up. This results in a loss of tire pressure. It’s not much, but it helps counteract (at least a little) the increase in temperature.
More about how altitude affects tire pressure here. (That article also mentions resetting cold tire pressure the next morning after you arrive at your destination.)
I hope that helps! (And yes, your TPMS may freak out a bit in the meantime if it ‘hits’ the high-pressure alarm setting, but it didn’t for me on my trip a few days ago.)
I check tire pressures and lug nuts everytime I hitch up. I carry a Ryobi 18volt unit, a 110 volt to plug in, and when all else fails, a foot pump.
Hey Donald,
Thanks for the comment! Sounds like you have your bases covered when it comes to tire inflation. I keep my Viair in my tow vehicle at all times, as does Kelly. Since we are usually towing together, we too have backups.
Why are you only reviewing one brand? What about ARB or other makes?
Hey John,
While there are many, many brands of 12-volt portable air compressors, we chose to feature only Viair for the reasons that we explain here.