Measuring Truck Tire Inflation Pressures

It is essential to keep truck tires properly inflated so they can carry the load, wear evenly, maximize fuel mileage, and maintain their integrity. Chronic overdeflection (overinflation, underinflation, or a combination) is a common cause or contributor to tire failures.

During pre-trip inspections, the Federal Motor Carrier Safety Regulations (49 CFR  §396.13) requires the driver “be satisfied that the motor vehicle is in safe operating condition.” This includes the truck’s tires . As part of that pre-trip tire inspection, a driver is trained to look for low or flat tires. But there is no requirement that the driver check the air pressure with a gauge. In fact, while going through truck driving school before getting my CDL, we never once used an air pressure gauge during our pre-trip inspection lessons, daily routines, or exams.

It would be an onerous task to require a driver to check the air pressure of all eighteen tires on a typical tractor trailer before every trip.  As an alternative to a gauge, some drivers use a “tire thumper” (usually a rubber mallet or some kind of a bat) to check their tires. If a tire is inflated, the thumper would bounce right off. Striking a tire with little or no air would have no bounce back, but would respond with a flat thud. While a thumper can’t determine if a tire is properly inflated, it can let you know if a tire is flat or near flat. [Click on image to enlarge, then click back arrow to return to this post.]

Only the bottom four of these will give you an accurate truck tire inflation pressure. (Made with ZEISS Milvus 50 mm f/2 Macro lens on Nikon D850 at f/16, 1/200 sec, ISO 64. Used one Profoto B1x studio strobe with silver umbrella with diffuser on each side.)

Back in 1998, I bought the Trucker’s Toothpick & Tire Tester at the top of the photo at a truck stop just for fun. (Both the name of the product and the company are rather whimsical.) It is a weighted metal stick with a hand grip on one end and a protective cover on the other. Along with various wooden bats, it is typical of tire thumpers sold commercially. While their benefits are minimal, at least thumpers prevent a driver from starting off on a trip with a flat tire.

The three stick gauges in the middle of the photo look similar, but their dual heads are at different angles. One of them is bound to fit when the metal valve stems of either the inner or outer tire of a dual pair are bent and otherwise inaccessible. They prevent you from bleeding air out of the tire as you try to get the gauge head to seat on the valve.

Stick gauges seem tricky to read until you understand how their scale works. I’ll describe that below.

The digital pressure gauge at the bottom is the easiest to read (and photograph, if you do that—I don’t).

Here’s how to read a truck tire stick gauge. Assume you’ve just checked the air pressure of a steer axle tire and got the reading below. [Click on image to enlarge, then click back arrow to return to this post.]

Scale on truck tire inflation pressure gauge. (Made with Nikon 105 mm Micro lens on Nikon D850 at f/16, 1/200 sec, ISO 64. Used one Profoto B1x studio strobe with silver umbrella with diffuser on each side.)

At first glance, the scale might not seem to make sense with the decimals between the longest hash marks. (Gauges typically start at 10 psi, not 0 psi; anything less than 10 psi is obviously flat.)

Zooming in might help make deciphering the scale more clear. (This photo has been rotated clockwise to be oriented as you would read the scale in use.) [Click on image to enlarge, then click back arrow to return to this post.]

Rotated close-up of scale on truck tire inflation pressure gauge.(Made with Nikon 105 mm Micro lens on Nikon D850 at f/16, 1/200 sec, ISO 64. Used one Profoto B1x studio strobe with silver umbrella with diffuser on each side.)

Let’s start with the 100 psi mark. (Note that on this gauge, the 100 psi hash mark happens to intersect the second zero.) The next short hash mark down represents 102 psi. One shorter hash mark down is 104 psi. Just below that, the longer hash mark near the center of the scale represents 105 psi. The next short hash mark at the right edge below that is 106 psi. Below that, the short hash mark is 108 psi. Next is the longer hash mark for 110 psi. Using this information, you can see the inflation pressure reading above was 118 psi.

To summarize, all the hash marks along the right edge of the scale are in 2 psi increments. Half way between the decimals, the longer hash marks near the center of the scale are in 5 psi increments.

Anywhere along the scale, anytime the end of the barrel is halfway between two consecutive short hash marks, the inflation pressure is 1 psi greater than the short hash mark above it.

Takeaways:

-1- While truck tires must be properly inflated, the Federal Motor Carrier Safety Regulations do not require truck drivers to check tire inflation pressures with a gauge during their pre-trip inspections.

-2- Tire thumpers can indicate if a tire is flat or almost flat, but cannot determine the inflation pressure.

-3- Different angles of dual head inflation pressure gauges can help access bent valve stems.

-4- If using a stick gauge, make sure you accurately read the scale.

Adding Flash to Show Depth

In an earlier post, I showed how shooting a sponge with a side flash gave depth to its surface that couldn’t be shown using a direct flash. I used a sponge since sponges are small, readily available, and easy to practice with anywhere. In this post, I’ll show how a side flash gives depth to an automotive subject—namely, a tire tread.

For this first image, I didn’t use any flash, but adjusted the camera for a proper exposure for the ambient light. It’s properly exposed, but the depth and extent of the cuts and chips out of the tread aren’t apparent. (Click on photo to enlarge, then click on back arrow to return to this post.)

Perpendicular to tread with no flash. (Made with ZEISS Milvus 50 mm f/2 Macro lens on Nikon D850 at f/16, 4.0 sec, ISO 100.)

This photo was made in my Studio Lab, which has so many LED shop lights overhead people say it looks like an operating room. Even though the room looks bright to our eyes, there is not as much ambient light for photography as you might think. In fact, to make the image above required a 4.0 second shutter speed, which obviously precluded handholding the camera. (I also increased the ISO 2/3 stop from 64 to 100.)

For the second shot, I added a Profoto B1x flash to each side, almost perpendicular to the camera, shooting across the tread. I triggered them with a Nikon SB-910 flash in the hotshoe that was pointed straight up at a very low power so it would not contribute to the exposure. (Click on photo to enlarge, then click on back arrow to return to this post.)

Perpendicular to tread with one flash to each side. (Made with ZEISS Milvus 50 mm f/2 Macro lens on Nikon D850 at f/16, 1/200 sec, ISO 64. One Profoto B1x strobe to each side triggered by a Nikon SB-910 flash in the camera’s hot shoe.)

Side flash enhances texture by creating shadows. Diffused ambient light and direct flash lighting both evenly light your subject, which fills in the shadows, which, in turn, reduces the appearance of any textures.

[Technical aside #1: With cross-light from the added side flashes, the shutter speed was 9 2/3 stops faster at 1/200 second and the ISO was 2/3 stop less at 64, for a total of 10 1/3 stops less light than the first shot. If the flashes were turned off for the second photo, that exposure would have resulted in a pure black image. The flashes were adjusted to give the proper amount of light for the exposure. This is called a full flash image, where all of the light is provided by flash. This differs from a fill flash image where the light from any flash enhances the ambient exposure, but flash isn’t the only light source. More on this later.]

[Technical aside #2: For an equivalent ambient light image, instead of a 4.0 second shutter speed and ISO 100, you could use 1/60 second shutter speed and ISO 256,000. The 1/60 second shutter speed may allow you to handhold the camera, but ISO 256,000 is guaranteed to be extremely noisy and noticeably lacking in dynamic range. Not a good alternative at all.]

Four major takeaways:

-1- As with the earlier sponge example, flash light coming from the side brings out texture by creating shadows.

-2- Both diffused ambient light and direct flash lighting flood every surface with the same light, obscuring texture and depth differences.

-3- Indoor ambient light may look bright to our eyes, but it will require very long exposures or an extremely high (and noisy) ISO to make the photograph.

-4- You must adjust your exposure accordingly when going between ambient  light and full flash lighted images.

My YouTube Interview about Automotive Forensic Photography

On Thursday, April 1, 2021 (and, no, it wasn’t an April Fools joke), I had the honor of being interviewed by Eugene Liscio of ai2-3D  for his Forensics Talks YouTube channel.

Forensics Talks YouTube interview by Eugene Liscio

Here’s a link to the interview: Forensics Talks with Tom Vadnais.

For almost an hour, we talked about a wide range of topics related to tire, vehicle, and accident reconstruction photography. Among the subjects we discussed were the importance and use of a tripod, a polarizer, and flash. We also touched on both kinds of night photography and on post-processing.

I hope you will find the information we discussed useful. The interview also gives an idea of a couple of the topics which we demonstrate and discuss in depth in my SAE class which, by the way, will be resuming as in-person classes this year.

Here’s a link to that class: SAE C1729. I’ll post the dates of the new classes as soon as we finalize them.

Photographing Under Flaps or Broken Pieces

Often, you’ll find you need to photograph underneath a small flap, tear, or partially broken piece. It’s quite difficult to hold the piece steady, align the lights, keep the piece perpendicular to the camera, frame the image, focus, and hold the camera steady simultaneously. Unless you have unusually long arms, many times it will be impossible to even look through the viewfinder or at the rear LCD while holding both the camera and piece, much less holding them both still and properly aligned.

You’ll want to frame your subject without cutting off important parts of it, showing lots of excess space to any side, or ending up with strange subject angles. Particularly with close-up and macro images, you’ll also want to maximize the depth of field by keeping your camera sensor perpendicular to the piece. 

The only reliable and repeatable way to ensure you can get the camera where you need it—while keeping everything aligned and stationary—is to hold the piece with a clamp and support your camera with a tripod, studio stand, or even a beanbag. When both the camera and the subject are held still, you can frame the subject through the viewfinder or with the LCD, adjust the lights, and take test shots until you get your lighting just where you need it. (Click on the image to enlarge it, then click the back arrow to return to this post.)

Setup for photos of sidewall flap. (Made using Nikon D850 with 55 mm ZEISS Otus lens. Lighting: Two Profoto B1x studio strobes. Exposure: f/16, 1/200 sec, ISO 64.)

For the torn sidewall rubber of the tire above, I used a Wimberley The Plamp II with its base clamped on the tire bead and its smaller subject clamp on the rubber flap. This securely held the flap in place so I could compose the shot and ensure the camera sensor was perpendicular to the underside surface of the flap. In my Studio Lab, I use a Foba camera stand to both place and support the camera precisely where I need it. In the field, I would use a tripod.

I held the off-camera flash in my left had so I could aim it where I wanted it, and tripped the camera’s shutter with a remote shutter cord in my right hand. (A self-timer could work, too.)

This resulting image below was an overall view of the flap and tire carcass ply surfaces that had pulled apart. It was made with a ZEISS Milvus 50 mm macro lens.  (Click on the image to enlarge it, then click the back arrow to return to this post.)

Sidewall flap. (Made using Nikon D850 with 50 mm ZEISS Milvus macro lens. Nikon R1C1 flashes with Nikon SB-910 to left side. Exposure: f/16, 1/200 sec, ISO 64.)

For overall lighting, I used two Nikon SB-R200 macro flashes on the R1C1 ring around the lens with one below and one to the right of the lens. To show the texture on the sidewall rubber and the polyester carcass cords, I used a Nikon SB-910 flash off camera to the left. (All the remote flashes were controlled via infrared from a Nikon SB-910 flash on camera in master mode.)

In the closer image below, I repeated the process using a ZEISS Milvus 100 mm macro lens to fill the frame with the torn surface textures. For a good composition, I had to reposition the camera, which was straightforward with the Foba camera stand. (Click on the image to enlarge it, then click the back arrow to return to this post.)

Sidewall flap. (Made using Nikon D850 with 100 mm ZEISS Milvus macro lens. Nikon R1C1 flashes with Nikon SB-910 to left side. Exposure: f/16, 1/200 sec, ISO 64.)

Main takeaways:

-1- Flaps and pieces should be held steady with some sort of clamp. It’s almost impossible to hold them in place by hand.

-2- Securely support the camera in position for the best composition and maximum depth of field using a tripod, studio stand, or even a beanbag.

-3- Align camera so its sensor is perpendicular to your subject to maximize depth of field.

-4- Use sidelighting in addition to overall lighting to show texture (or lack of texture).

Vadnais Engineering Studio Lab

To facilitate my tire, wheel, and product analysis and photography, I set up my Studio Lab in my basement. Although it continues to evolve, it had fortuitously been set up and in use for nine years before the COVID-19 pandemic of 2020 brought most travel and meetings to a halt. In fact, even before the pandemic, I have preferred having tires, wheels, and other products shipped to me for analysis and/or photography in my Studio Lab rather than traveling to where they might be stored.

In my Studio Lab, I have all the inspection and photography equipment I need to do a complete analysis and documentation, regardless of what I encounter. Besides, I can leave any setup in place for several days if needed. (Click on an image to enlarge it. Then click back arrow to return to this post.)

Tire analysis setup includes camera with flash on studio stand, two studio strobes into silver umbrellas, silver reflector, and gray background paper with tire on lazy susan. (Made with ZEISS Milvus 25 mm f/1.4 lens on Nikon D850 with SB-910 flash firing the two studio strobes, f/16, 0.5 sec, ISO 64.)

Although it is partly obscured by the support pole in the photograph above, I mount a camera on one end of the sliding arm of a Foba rolling studio stand. One of my favorite pieces of gear, a studio stand is much faster to adjust and move than a tripod. The arm rotates around, slides back and forth on, and moves up and down on a solid pole mounted to a base with three lockable wheels. These adjustments allow a camera to be brought and held in the exact position needed—both rapidly and securely.

I then mount as many lights as required on rolling light stands, floor stands, C-stands, or clamps. Having the camera and lights on rolling stands makes it quick and easy to change their positions. My large collection of reflectors and reference scales can be held in position with a variety of clamps, as needed.

I also use one of three wooden or four plastic lazy susans, depending on the size of the tire, wheel, or product. I cover the lazy susans with gray paper or cloth, and use a neutral gray background paper from a large ceiling-mounted roll.

Because tires and wheels are usually neutral in color—shades of black, gray, silver, or white—the neutral gray background neither clashes nor contaminates the subjects. With other products, I may use gray, black, or white backgrounds.

I’ve installed so many LED shop lights overhead that a couple visitors have described the area as bright as an operating room. Even with this much light, I still use a number of LED drop lights during inspections, and to assist with composition and focusing while photographing. (Click on an image to enlarge it. Then click back arrow to return to this post.)

Tire analysis setup includes camera with flash on studio stand, two studio strobes into silver umbrellas, silver reflector, and gray background paper with tire on largest lazy susan. (Made with ZEISS Milvus 25 mm f/1.4 lens on Nikon D850 with SB-910 flash, f/16, 0.6 sec, ISO 160.)

I will describe lighting for specific items in future posts, but for tires, I generally use two Profoto B1x 500 W/s studio strobes firing into Profoto Medium Deep Silver umbrellas—both mounted on rolling light stands. A Nikon SB-910 flash affixed to the hot shoe a Nikon D850 DSLR  camera triggers both studio strobes, and adds its light on the subject, too. A silver Profoto reflector bounces light onto the tread or belt surface.

If you’re wondering, I use the purple trekking pole to rotate a tire while I’m sitting on the Wen mechanic’s rolling seat behind the camera. Using that pole allows me to look at the image through the grid in Live View on the camera’s LCD while I precisely line up the position stickers on the tire with the gridlines.

The cable hanging from the camera is the remote shutter release. With this, I can trip the shutter without touching the camera to insure there is no motion blur in the photo.

I will share more of the techniques and gear I use in future posts.

Lighting Equipment Used for the Previous Low Light Blog Post

In the last post, I showed some lighting solutions to use when your subject is in low light. In this post, I will briefly describe some of the supports and the lights I referred to. Flash is a big and interesting subject, and I have an entire module on flash photography in the photography class I teach for SAE (SAE C1729). Or, I should say, will resume teaching once this pandemic eases.

I will expand on each of these in future posts, but wanted to give the basics here. First and foremost is using a good tripod. There is nothing better you can do to improve your photographs than to use a tripod. I use a tripod in any kind of light for almost every image of any subject, including accident sites, vehicles, tires, and other products. A good tripod is even more essential when the light levels are low.

It used to be unusual to see someone with a tripod at an inspection. But with so many scanners now being used, tripods have become quite common. So there goes one excuse for not carrying and using one!

I have a post all about tripods in the works, but for now I’ll just mention the Really Right Stuff (RRS) TVC-24L with a RRS BH-40 ball head that I use for all inspections out of my Studio Lab. It is compact and lightweight, yet it extends quite high, which is essential. All of my tripods have LensCoat LegWraps for insulation (from both hot sun and freezing temperatures) and for comfort in carrying. (Click on image to enlarge, then click on back arrow to return to this post.)

Really Right Stuff (RRS) TVC-24L tripod with RRS BH-40 ball head. (Made using Nikon D850 with ZEISS Milvus 50 mm macro lens. Lit with two Profoto B1x strobes firing into silver umbrellas.)

While future posts (and classes) will discuss flash techniques in detail, in this post I will focus on the equipment I used in the previous post.

Flashes that fit in your camera’s hot shoe are generically called speedlights or flashes. In fact, Nikon calls their flashes Speedlights while Canon calls theirs Speedlites. Larger studio-type flashes are referred to as strobes. Here are some examples from the front. All are battery powered. (Click on image to enlarge, then click on back arrow to return to this post.)

(L to R) Profoto B1x, Canon 430EX III-RT, Nikon SB-910, and Profoto B10. (Made using Nikon D850 with ZEISS Milvus 50 mm macro lens.)

And here they are from the rear. Note that the speedlight flashes can be mounted in a camera hot shoe or on a light stand. (Click on image to enlarge, then click on back arrow to return to this post.)

(L to R) Profoto B1x, Canon 430EX III-RT, Nikon SB-910, and Profoto B10. (Made using Nikon D850 with ZEISS Milvus 50 mm macro lens.)

In the photograph of the lighting setup in the previous post, there was a Nikon SB-910 Speedlight in the camera hot shoe and two Profoto B10 strobes on Manfrotto 5002-M travel light stands. These stands are lightweight and fold up small, yet are quite sturdy. (Click on image to enlarge, then click on back arrow to return to this post.)

Manfrotto travel light stands 5002-M (top) and 5001 (bottom). (Made using Nikon D850 with ZEISS Milvus 50 mm macro lens. Lit by two Profoto B1x strobes firing into silver umbrellas with diffusers.)

This final image shows a Profoto B10 mounted on a Manfrotto 5001, which is slightly smaller and slightly less sturdy (though still sufficient) than a 5002-M. (Click on image to enlarge, then click on back arrow to return to this post.)

Profoto B10 on Manfrotto 5001 travel light stand. (Made using Nikon D850 with ZEISS Milvus 50 mm macro lens. Lit with two Profoto B1x strobes firing into silver umbrellas.)

In the previous post, the two B10’s were fired through their infrared slave sensors when they sensed light from the on-camera Nikon flash. All three flashes and the camera’s exposure settings were all manually set.

Why use strobes when you can use speedlights? Power is the answer. Mid-to-high end speedlights typically have power outputs between 60 and 150 Watt-seconds (Ws), while the Profoto B10 and B1x are 250 and 500 Ws, respectively. This means you’d need two-to-eight speedlights to equal one Profoto strobe. For example, you’d need sixteen 60 Ws mid-range flashes to equal the power output of the two 500 Ws strobes I use for tire photos in my Studio Lab. Not only would those be unwieldy to set up, but think of how many AA batteries you’d need!

Why is flash power important? Every one stop increase in exposure requires doubling of the light power. For forensic or testing photographs, you want to minimize noise by using the lowest ISO you can, and you want a deep depth of field by using a smaller (higher number) aperture. Both a lower ISO and a smaller aperture result in less light reaching the sensor. Consequently, the flash has to be powerful enough to ensure a proper exposure without raising ISO or opening up your aperture.

Future posts will go deeper into exposure both with and without flash. We will be using this equipment throughout.

Making Photographs in Low Light

Most accident reconstructionists and product liability engineers have had to photograph a vehicle, vehicle component, or other product in a dark area such as a warehouse, storage facility, lab, or even an office. Conditions can be even worse for building or fire investigators, especially if the power is out. By definition, what is missing in any of these situations is light!

But despite the lack of light, you might only get this one chance to inspect the evidence. You’ve got to come back with well-exposed, well-lit professional photographs—photos that accurately portray what you saw, represent you well to your clients, and reflect the quality standards of your work, especially during depositions and trials.

Unless you are trying to capture a low light scene as it is (which is a completely different discussion), you have several options to make a photo in low light.

One is light painting by moving a flashlight over your subject during a long exposure. This is tedious and time-consuming, especially if you have to make more than one or two images. It is also hit-and-miss, even if you are experienced with it. Of course you need a sturdy tripod for every shot, since the exposures are long. These long exposures also risk generating noise. So light painting might be good in an emergency, and it’s sometimes necessary for illuminating  vehicles at nighttime accident scenes.

It can work, as shown below, but it’s not recommended for making inspection photographs. This photograph of a rental car was made at dusk with no lights on in the garage. The only light came from when I walked around the vehicle constantly moving a flashlight, painting both the car and the garage bay. Note how the long (74 second) exposure made the outdoors look brighter than it was. (Click on image to enlarge, then click back arrow to return to this post.)

Light painting at f/11 and ISO 64 with shutter speed of 74 seconds. (Made using Nikon D850 with ZEISS Milvus 25 mm f/1.4 lens on RRS TVP-45 tripod.)

Another option is use high ISO sensitivities. On all digital cameras, the higher the ISO, the more noise and less dynamic range there is. With newer cameras, neither the increased noise nor the dynamic range loss are obtrusive until the middle or higher ISO values (say ISO 800 or even 1600). Here’s an example made at ISO 200,000 and cropped from the full frame. (Click on image to enlarge, then click back arrow to return to this post.)

Crop of an image made at f/16, 1/60 sec, ISO 200,000 showing noise. (Made using Nikon D850 with ZEISS Milvus 50 mm macro lens, no flash.)

As a third option, continuous light sources are better than nothing, but none are bright enough to avoid having to use a long shutter speed and/or to raise your ISO. Most fluorescent lights flicker and have an undesirable color cast. Halogen shop lights get hot and have a very warm color cast. Quality LED lights have good color control, but still aren’t bright enough. Even the larger LED panels made for photo studios don’t put out enough light, plus the brighter ones are big and unwieldy to transport and setup. Again, none of them put out enough light to allow a low ISO and a shorter shutter speed.

Flash is your best option, by far. But the tiny built-in flash on a point-and-shoot, the popup flash on a DSLR or mirrorless, or even a professional flash in your camera’s hot shoe won’t always be sufficient. You’ll need additional light.

There is a learning curve to using flash, since you can’t see the effect of the light until after you’ve made the photograph. But as long as you think about where and about how much light you need, it’s something you’ll pick up with a little practice.

Since I shoot Nikon, I always carry three Nikon Speedlights (flashes) with me. (You don’t need flashes made by your camera manufacturer, but those will always work with your camera, and are usually quite robust.) One flash goes in the camera’s hot shoe, and I put the other two where needed. I usually carry two small, lightweight, travel light stands with me so I can place the lights where they will do the most good, but I will often just prop them up on something nearby. (Within the next couple days, I will write a post about the gear I mention in this post.)

Since I do a lot of tire analysis, I often need even more light than the Speedlights can put out. Besides, Speedlights can take a long time to recharge their capacitors between shots.

Especially for tires, I use Profoto B10 battery-powered studio flashes on the road and battery-powered Profoto B1x studio flashes in my Studio Lab. Again, more on these in a post later this week.

Recently, I had to inspect tires and wheels inside a semi-trailer. Even though my inspection was close to noon on a sunny day, and the trailer had a couple side doors I could open, I knew it would be pretty dark inside the trailer for photography. I set up my two Profoto B10 flashes on my travel light stands. They were fired by a Nikon SB-910 flash in my camera hot shoe. Exposure and flash powers were all set manually. (Click on image to enlarge, then click back arrow to return to this post.)

Tire and wheel inside semi-trailer. (Made using Nikon D850 with ZEISS Milvus 35 mm lens and on-camera Nikon SB-910 that also fired two Profoto B10s.)

Here is a resulting image from that setup. (Click on image to enlarge, then click back arrow to return to this post.)

Tire and wheel inside semi-trailer. (Made using Nikon D850 with ZEISS Milvus 50 mm macro lens and on-camera Nikon SB-910 that also fired two Profoto B10s.)

A single flash on the camera—even Nikon’s most powerful Speedlight—could never have provided enough light to evenly illuminate this tire and wheel. The Speedlight and battery-powered strobes not only provided nice even lighting, but allowed me to shoot at ISO 64, which is the lowest on a Nikon D850. This minimized the noise and maximized the dynamic range to show the most detail possible.

Checking Tire Pressures in Truck Tire Monitoring and Inflation and Systems

Tire pressure monitoring systems (TPMS) are required on cars, pickups, and SUVs, and can be found on some heavy trucks. A TPMS simply warns the driver that the air pressure in a tire dropped to a certain pressure, or dropped a certain percent below the programmed pressure. TPMS does not replenish the air. 

Onboard tire inflation systems, which are becoming common on air-braked trucks, semi-trailers, and buses, use the onboard air system to maintain the appropriate air pressure in each tire. Truck tire inflation systems only warn a driver if a tire loses air faster than the system can replenish it.

During routine maintenance, after a tire issue, or after an accident, you will often want to check all tire inflation pressures, even if there is a tire monitoring system or an onboard inflation system. You’ll need to ensure that either type of system was working properly. That requires checking each tire pressure individually.

With either system, how to you access the valve for each tire? Below are two examples.

First is a Stemco AirBat RF tire monitoring system on the rear tandems of a three-axle truck tractor. (Click on image to enlarge, then click on back arrow to return to this post.)

Stemco AirBat RF assembled. (Made using Nikon D850 with ZEISS Milvus 50 mm macro lens and Nikon SB-910 flash.)

There are two standard metal valve caps—one for each tire of the dual. Remove these caps and use a truck tire pressure gauge as you normally would. You can also add air through these valves if required. (Click on image to enlarge, then click on back arrow to return to this post.)

Stemco AirBat RF with valve caps off. (Made using Nikon D850 with ZEISS Milvus 50 mm macro lens and Nikon SB-910 flash.)

Make sure you know which valve goes to which tire. It’s easy to do; just trace the hose back to its associated wheel.

As an example of tire inflation systems, the Meritor Tire Inflation System by P.S.I. (MTIS) is a popular system on both new and retrofitted semi-trailers. (Click on image to enlarge, then click on back arrow to return to this post.)

MTIS by P.S.I. assembled. (Made using Nikon D850 with ZEISS Milvus 50 mm macro lens and Nikon SB-910 flash.)

With MTIS, twist the knurled fitting at either end of the through tee, then use your truck tire pressure gauge on the valve at the end of each hose. Again, make sure you trace which hose goes to which tire. (Click on image to enlarge, then click on back arrow to return to this post.)

MTIS by P.S.I. valve stem. (Made using Nikon D850 with ZEISS Milvus 50 mm macro lens and Nikon SB-910 flash.)

While these systems initially look intimidating, it is actually much easier to check tire inflation pressures with them than it is trying to get a tire gauge to fit on individual valve stems on the wheels.

Using Off-Camera Flash to Bring Out Details

A couple posts ago, I showed examples of bringing out textures in a sponge by creating shadows using an off-camera flash. Here is an example with the type of photography subject we are more likely to encounter.

Vehicle wheels and other components are often stamped with model and serial numbers, along with with dates of manufacture. If you use a built-in flash or a flash mounted in the camera’s hot shoe, those stampings will often be invisible in your photograph. (Click on image to enlarge, then click on back arrow to return to this post.)

Stamping in wheel flange with flash in camera hot shoe. (Made using Nikon D850 with ZEISS Milvus 50 mm macro lens and Nikon SB-910 flash.)

This photo is properly exposed, but is useless in documenting the wheel. The key is to get the light at an oblique angle so it skims across the surface to create both light and shadow, just like we did with the sponge. (Click on image to enlarge, then click on back arrow to return to this post.)

Stamping in wheel flange with flash off camera almost perpendicular to the right. (Made using Nikon D850 with ZEISS Milvus 50 mm macro lens and Profoto B10 strobe to camera right.)

For this second photograph, I used a Profoto B10 strobe to the camera’s right, almost perpendicular to the stamping. I fired that strobe with the flash in my camera hot shoe, but I made sure the hot shoe flash did not affect the exposure. I used a B10, but could just as easily used another Nikon flash to get the exact same effect. I had already been using the B10 for other shots, so I just used that. In fact, it would have been even easier with second Nikon flash, since I could set the hot shoe flash to Master with no light output while the other flash would be set to Remote with either manual or TTL flash.

This second image is also properly exposed, but now the direction of the light makes this photo useful. Now you can see it is a 22.5 x 8.25 Accuride wheel manufactured 10/19/17.

The point is that you need to consider both the amount and direction of light to properly illuminate a subject. Light illuminates your subject, but the shadows give it definition. Shadows are essential in a 2-D depiction of a 3-D subject, especially when you need to show textures or depth.

Photo Composition: Too Much Wasted Space

I’m sure you’ve seen many photos like the one below. [Click on image to enlarge, then click back arrow to return to this post.]

Left front of truck with bad composition. (Nikon D850 with ZEISS Milvus 50 mm f/2 macro lens and Nikon SB-910 fill flash.)

What is the subject? The tire and wheel? The intruding part at the upper right (which was actually from an unrelated truck)? The gravel? Is there something important that I should be seeing in the gravel?

It was actually the tire and wheel. But if you draw a vertical line down the middle of the photo, almost the entire right half of it is unrelated to the subject.

In the image below, the tire and wheel are still featured, but now you can see how they relate to part of the truck’s frame rail and steering system, too. [Click on image to enlarge, then click back arrow to return to this post.]

Left front of truck with good composition. (Nikon D850 with ZEISS Milvus 50 mm f/2 macro lens and Nikon SB-910 fill flash.)

This photo makes more sense and eliminates unnecessary and confusing elements. It’s easy to pay so much attention to your subject that you forget what it looks like in the frame. Make sure you haven’t included too much empty space or too many unrelated elements that are not only distracting and confusing, but look sloppy, careless, and unprofessional.