How to calculate proper tire pressure


Tire Pressure Calculator | Overland Racks Ontario


Back by popular demand

Since transitioning to the new website, we have not had our tire pressure calculator live on the site.

Having had numerous people reach out asking for it back, we figured it was time.

A little legal mumbo jumbo:

As always – feel free to use this as a reference guide for informational/testing purposes.
We are not responsible for any injuries or damages caused by following this calculator.


Importance and Theory Behind Tire Pressure

Correct tire pressure is one of the most important, yet often the most overlooked components to setting up an overland vehicle or street driven, off-road truck.
If you want a little more information, continue reading here. Otherwise, scroll down to the next section for our tire pressure calculator.

Tire pressure affects the vehicle’s handling, tire wear, fuel economy, ride quality, and braking performance.

Under-inflated – Under-inflated tires will cause a decrease in fuel economy due to an increased rolling resistance as well as poor handling. 
Tires will also wear faster on the outside of the tread and cause excess heat buildup that could result in catastrophic failure.

Over-inflated – Over-inflated tires can actually increase fuel economy, but the benefits stop there. The minor savings on fuel are outweighed by the faster tire wear.
Tires will wear faster in the center of the tread, and will be more prone to skidding due to the lack of tread contact with the pavement.

Properly inflated – Properly inflated tires optimize tread wear, handling, ride quality and breaking performance.

When installing a tire size that is not the manufacturer’s recommended size, the factory tire pressure goes out the window.

All tire manufacturers are required to meet specific load carrying standards set out by the Tire and Rim Association.
Different tire sizes will support different loads at various pressures.

As an example of this consider the following:
​A single 37×12.50R17 tire is rated to support 2150lbs at 25psi. 
A single 42×14.50R17 tire is rated to support 3085lbs at 25psi.

That represents a 30% difference in load carrying ability when set at the same pressure.

The basic principle at play here is that weight is supported by a specific VOLUME of air. Not pressure.
Therefore, as tire sizes increase, a lower PSI is required to support the vehicle weight when all else is equal.


Calculate Your IDEAL Tire Pressure

In order to get the most out of your tires as described above, the following calculator will provide you with the ideal baseline for your trucks tire pressure with any given tire.

In order to be accurate you must know the weight of YOUR truck front and rear. Simply utilizing the manufacturer’s specified weights will not necessarily be accurate – items such as a winch, added skid plates, steel bumpers or rock sliders, cargo and even people, all add significant weight to the vehicle.

The most accurate way to obtain the weight is on a scale at a truck weigh station or recycling center.

If you are unsure of your vehicle weight and unable to obtain an accurate weight – utilize the gross vehicle weight rating (GVWR) provided on the door jamb of your vehicle. This is the maximum weight the vehicle is rated to carry fully loaded.

***Always test tire pressures with the chalk test, or an infrared heat meter. This calculator will give you a very good base tire pressure based on the weight and tire specifications that YOU enter.

***We are not responsible for any injuries or damages caused by following this calculator. 


Calculator Instructions

Fill in the required values in the order shown on the calculator:

  • Front Weight – Total weight on front axle
  • Rear Weight – Total weight on rear axle
  • Tire Max Load – Maximum load printed on your tire’s sidewall in LBS
  • Tire Max Pressure – Maximum pressure printed on your tire’s sidewall in PSI

After the required values are entered, you will see a recommended pressure for both the front tires, as well as the rear tires.

These pressures include a 5% safety margin to help account for the unexpected.

As mentioned previously, test your results with the chalk test!

***We are not responsible for any injuries or damages caused by following this calculator. Test results yourself to ensure accuracy.


Determining the Right PSI - Tire Review Magazine

More than a few of us have spent time looking for the placard with a vehicle’s tire pressure recommendations. And more than a few consumers have looked at their owner’s manual or that elusive placard and wondered why the pressures there are different from the maximum pressure on the tire’s sidewalls.

How do the automobile manufacturers and their tire suppliers come up with those numbers?

It starts with the load the vehicle is designed to carry and the size of the tires installed on it. Worldwide, several organizations exist with the primary purpose of establishing and publishing interchangeability standards for tires, wheels, valves and allied parts.

In the U.S., this standardizing body is the Tire and Rim Association (TRA). Its European equivalent is the European Tire and Rim Technical Organization (ETRTO). The Japanese Automotive Tire Manufacturers Association (JATMA) has that respon-sibility in Japan. There are other similar organizations, but those three are the major players.

None of the major standardizing organizations is government mandated or regulatory. The organizations, and the standards that they set, are all voluntary. There is no legal obligation for any tire or auto manufacturer to abide by the standards. However, for practical and legal liability purposes, it simply makes sense to follow the standards and all vehicle and tire manufacturers use them.

While TRA, ERTO and JATMA all use slightly different protocols, they consult with each other and their standards are all very close. These organizations establish a range of standard dimensions for each tire size so that the proportions of all tires of a particular size are very similar. This assures that all tires of a specific size are interchangeable, at least in terms of their physical dimensions.

They also set each tire’s “load curve,” which is the relationship between inflation pressure and the tire’s maximum load carrying capacity. Like the size standards, there are some slight variations among the different organizations’ load curves, but they are not significant.

Part of each load curve standard is the point at which the load curve stops going up. For TRA p-metric standard load tires, it is at 35 psi. Equivalent ETRTO and JATMA tires peak at 36 psi. Interestingly, all of the standardizing organizations agree that standard load passenger car tires can (and should) use optional higher inflation pressures (44 psi or 51 psi) for certain circumstances such as high speed driving. However, these higher inflation pressures generally provide no increase in load carrying capacity and in some circumstances specify a reduction in load for high-speed use.

So the auto manufacturer knows what a vehicle weighs and knows how much weight can be added in fuel, passengers, cargo, etc. They can look at the load curve of the particular size that they have selected. To this number, auto manufacturers usually add a safety factor of around 10%.

The Ford-Firestone Factor

For passenger cars, SUVs and light trucks, the load curve number launches a series of negotiations. The engineers responsible for the vehicle’s handling are likely to lobby for additional inflation pressure to improve handling. Similarly, lower rolling resistance results in better fuel economy and leads to demands for higher inflations. Cars likely to see high-speed bring with them engineers insisting on more air pressure. On the other hand, ride considerations are an important consideration and that calls for lower inflation pressures.

Today, the results of these nego-tiations are inflation pressures typically in the 32 psi to 35 psi range. If the champions of improved ride had their way, the 26 psi to 28 psi range that was common a few years ago would be more common. The safety factor of the higher inflation pressure seems to be carrying the day with automakers. After all, no one wants a repeat of the fiasco of when Ford set the recommended pressures on first generation Explorers at 26 psi.

In that situation, recommended inflation pressures too low to provide an adequate safety factor were frequently combined with poor maintenance, overloading and high ambient temperatures to produce a series of often-deadly accidents (250 deaths and 3,000 serious injuries were attributed to the problem).

Placard Placement

Other factors keep the process of determining recommended pressures from being completely cut and dried.

Aesthetics is often a big factor when automakers choose tire sizes, and the emphasis on style versus substance can complicate the negotiations. The popularity of extreme low-profile tires has required significant increases in recommended pressures. Cars likely to see significant high-speed often force auto manufacturers to lower load limits, move to higher tire speed ratings such as W or Y, or go to recommendations of up to 51 psi.

Although the process starts with load and seems like it would be simple, nothing is etched in stone.

The recommended pressures go onto the vehicle’s tire information placard once the engineers make their final decisions. Beginning in 2003, federal regulations required automobile manufacturers to place tire information placards in a standardized location and follow a common format. The tire information placards identify the OE tire sizes and inflation pressures (including the spare), along with the vehicle weight capacity.

All new vehicles must now have a placard located on the driver’s side doorjamb (the B-pillar). If a vehicle does not have a B-pillar, then the placard is to be placed on the rear edge of the driver’s door. And if the vehicle does not have a B-pillar and the driver’s door edge is too narrow, the placard is to be affixed on an inward facing surface next to the driver’s seating position.

In addition to providing the OE tire size(s) and recommended inflation pressure(s), vehicle manufacturers must also identify vehicle load capacity with the following sentence: “The combined weight of occupants and cargo should never exceed XXXX pounds.

For vehicles produced between 1968 and 2003, the original tires size(s) and inflation pressures were listed on a placard usually found on the driver-side door or doorjamb, rear passenger doorjamb, fuel filler door, glove box or center console door or inside the engine compartment.

Sometimes alternate pressures based on load or speed conditions are also provided.

The Sidewall Says

Consumers are often confused because federal safety regulations also require tire sidewalls to contain information about a tire’s maximum load capacity and maximum inflation pressure. For P-metric standard load tires, the maximum pressure listed on the sidewall will be 44 psi or 51 psi, even though the pressure where the maximum load occurs is 35 psi or 36 psi. On the sidewall, this would look like “Maximum Load XXXX lbs. Maximum Pressure YY psi.”

A few manufacturers interpret the regulation to mean the maximum load and the corresponding inflation pressure (“Maximum Load XXXX lbs. at YY psi”). Either way, too often consumers see the maximum inflation pressure on the sidewall and believe that is the correct pressure for their car.

Look at some of the online forums and you will see that the arguments about relying on the placard or the tire sidewall can be animated.

Regardless of the information on the tire sidewall, assuming the right size tire is installed on the vehicle the placard is the correct information.

While the maximum load of the vehicle is the primary factor in establishing the recommended pressures, many other considerations went into the calculations. Don’t make changes lightly. Varying from the vehicle manufacturer’s recommendations requires careful consideration of why you want to make the change and the possible safety implications.

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    Calculator works in test mode! Found an error in the indicators or want to leave suggestions, please send via the feedback form on the Feedback page or the VK group! Errors with evidence base (photos, screenshots, links) are accepted! All information presented on the site is for informational purposes only! Thanks for understanding!

    Contents

    • 1What pressure should the tires be?
    • 2 How is tire pressure measured?
    • 3Pressure gauges
    • 4Where does the manufacturer indicate the pressure ratings?
    • 5Peculiarities of inflating car wheels at different times of the year: winter and summer
    • 6Consequences of incorrect tire pressure selection
    • 7Tables of recommended tire pressure for different types of cars

    What pressure should be in tires?

    The correct tire pressure for car owners is not an idle issue. It affects the rate of wear of rubber, the quality of vehicle control, driving safety, fuel consumption. To control the level of inflation of the wheels, you need to know what the pressure in the tires of the car is measured in, and what devices are used for this.

    How is tire pressure measured?

    On the territory of Russia, the unit for measuring air pressure in tires is Atmosphere (1 atm. = 1 kgf / cm²) In the tables of manufacturers, the Atmosphere is often equated with another unit - Bar (1 bar = 0.98 atm).
    American automakers report values ​​in PSI (1 psi = 1 psi or pound/square inch).
    When marking car tires, manufacturers use Kilopascal (1 kPa = 6.895 psi) to indicate the maximum allowable pressure (MAX PRESSURE).
    Conversion of units of measurement is carried out according to the formulas:

    Important! Normal tire pressure does not depend on the brand of tires, but on the brand of your car and its manufacturer's recommendations. 3,0003

    9007.348 9024 9000 9000 9000

    025

    How to check the tire pressure of a car? For this, special devices are used - pressure gauges:

    Pointer

    Mechanical, spring type. Relatively inexpensive, gives readings accurate to 0.1 units

    Rack and pinion

    Coil spring. Reliable, affordable, easy to use

    Digital

    With digital display. A more modern alternative to mechanical devices

    Indicator cap

    Miniature device for each wheel. Sold as a set of four. It is screwed on instead of conventional caps, it works very clearly, the color of the indicator depends on the tire pressure

    External sensors-caps

    Electronic tire pressure and temperature indicator. Modern high precision online control device

    Important! Pressure measurements are made before a trip in "cold" tires, after several - at least 5, optimally 8 - hours of rest.

    Where does the manufacturer indicate the pressure standards?

    For the convenience of car enthusiasts, manufacturers place information about the correct pressure in the front and rear wheels so that it is always easy to refer to it. Reference plates in cars of different brands can be located on the central pillar on the driver's side, on the inside of the gas tank cap, on the end of the driver's door.

    Features of pumping car wheels at different times of the year: winter and summer

    Summer

    tire pressure can seriously increase. To avoid the possibility of tire explosion and other emergencies, when inflating wheels in summer, the following should be taken into account:

    • The increase in pressure in the wheels of a car with an increase in ambient air and roadway temperature can reach 10-15%. On the value corresponding to this percentage, it is better to “under-inflate” the tires;
    • during control measurements, it is necessary to take into account the increase in the time for equalizing the temperature inside and outside the wheels, it will be better if the car sits overnight;
    • about the maximum pressure in the front and rear wheels in summer and winter should be for your car, you can consult the accompanying documentation from the manufacturer. The difference will average 0.1-0.2 bar.

    Winter

    In winter, the cold and cooling of the road surface leads to a significant drop in pressure inside the wheels of the machine, which reduces its stability on the road. What are the features of inflating tires in winter:

    • In winter, it is better to check the pressure and inflate the wheels after the car has stood outdoors for at least 2 hours;
    • if the car was in a warm garage before leaving, calculate the temperature difference in the box and on the street, and then add 0.1 atm to the normal tire pressure for every 8-10 degrees of difference;
    • If the weather is stable and the thermometer does not show significant fluctuations, when inflating the tires, be guided by the "winter" pressure indicators recommended by the car manufacturer.

    Important! Even if you are not a professional driver, use the pressure gauge at least once a month and before every long journey. When changing the season with frequent temperature fluctuations, it is better to reduce this interval to at least 2 weeks.

    Consequences of incorrect tire pressure selection

    Do not underestimate the deviation of tire pressure from optimal values, in most cases it leads to negative consequences. Consider separately both options for changing the norm.

    Reduced pressure

    When the pressure gauge decreases, the contact of the wheel with the road is ensured only by the extreme points of its surface. Visually, this is practically impossible to determine, but this situation leads to a number of troubles:

    • the load on the side tracks of the tread increases, uneven rapid wear occurs;
    • road grip worsens, acceleration is delayed, the braking distance increases, the likelihood of skidding increases;
    • at high speeds, “wave formation” occurs in the side parts of the tires, which makes it difficult to stabilize the car in a critical situation, and also leads to destructive vibration of the tire carcass;
    • fuel consumption increases.

    High pressure

    When the pressure gauge readings exceed the optimal value, the wheel is in contact with the roadway only in its central part. As a result, the following happens:

    • grip with the road surface decreases, wheel stiffness increases, accelerated wear of the central tracks of the tire occurs;
    • there is a risk of tire burst when hitting bumps;
    • increased load on the chassis and body;
    • Noise level increases, driving comfort decreases.

    Different pressure

    In this case, there are a number of cases when a deliberate deviation of tire pressure from the norm by 10-12% can resolve a difficult situation. For example, lowering can help out on bumps, sand, viscous mud or wet grass - the wheel artificially becomes soft and behaves like caterpillars, increasing cross-country ability. Small pumping is shown when driving on highways at high speeds. Adding atmospheres for the rear wheels makes it easier to haul cargo.

    tables of recommended pressure in tires of different types of cars

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    TIRE PRESSURE - HOW TO CALCULATE CORRECTLY?

    Have you ever wondered in what pressure should be kept in tires of a non-standard size, for example 32x11.5R15?.. Have you ever wondered? And me too!
    Here, for example, on the plate in the door of the car, the size of the standard rubber looms, which you now don’t care about. Accordingly, the pressure indicated nearby on the same plate is now also up to you for the lamp, because. you already have completely different tires ... Soooo, what pressure should you keep in new tires now? Good question and let's figure it out together with you...
    The forum is often advised - I keep this much, and you keep it! This is of course a "strong" argument, and quite often experts in various pressures give advice like: "Average temperature in the hospital" But - the car, the wheels and I'm loved with such serious changes in the design as installing larger tires require clearer answers and grounds. And rightly so: therefore, I propose, without inventing anything, to turn to the facts and logic of tire manufacturers, who, it turns out, have scientifically substantiated and tested everything for a long time, and we just have to deal with this material.

    E a little more about the plates on the car body in different places. Please note that car manufacturers here, as a rule, are reinsured. The plates indicate the size of the budget tire itself and the pressure in it, they call such a tire a “regular” one. So, the indicated pressure is calculated for this regular tire for the maximum vehicle weight (taking into account the curb weight of the car, the weight of all passengers and the expected full load of the car with different luggage)! We very rarely drive with such a load and as a result it turns out that our tires are overinflated all the time. And as you know, tires with excess pressure destroy the suspension and the car itself with increased vibrations, and besides, the car behaves incorrectly on the road. The contact patch decreases - stability worsens, “oak” wheels reduce the comfort of movement to nothing: you sit like on a thresher, your wife constantly hangs over (like you bought a cart), everything in the cabin rumbles and falls off, flies so that you need to nail or weld. However, a heavily flat tire also has a number of other disadvantages: increased rolling resistance, poor handling, increased fuel consumption, and tire wear, and most importantly, a flat tire gets very hot, especially at speed or under load, as a result of which it quickly collapses. . There is only one way out - to find the optimal pressure option for a particular tire, a particular car and load. And now, in addition to all these details described above, you bought a set of tires of a non-standard or even huge size ... And what pressure do you want to keep in them now?

    P Therefore, I decided to collect data from professional sources on a number of tire sizes that we Jeepers use on our cars. And then from these data he deduced a table for calculating the optimal tire pressure for any SUV with different loads.
    Using such a table is quite simple : take the right size and see at what pressure in the tire, what will be the load capacity of the wheel. Then we multiply this value by your four wheels and get the estimated mass of the jeep with these tires. You just have to know in advance the curb weight of your SUV and add your own weight + the weight of a passenger or cargo. Based on data from M ichelin, Goodyear , BF Goodrich and Cooper tires, and their recommended pressures. However, when traveling long distances, it is still necessary to take into account that the tire pressure must be raised by three to four tens of atm, because. at a long constant speed, the tires get very hot, the tire compound softens, and the tire becomes more susceptible to damage. With an increase in speed, the frequency of tire deformation cycles increases, that is, dynamic loads increase, friction increases, shock loads increase. All these conditions reduce tire life. Again I have to write vile things, but what to do - the technique requires a logical approach and accuracy!
    For convenience, in the table at the end of each line, the dimensions of the installation rim width (in inches) for each tire size are given (the allowable rim width for a specific tire size from - to, in red - the recommended rim width for this tire).


    Sorry for the photo from the monitor, otherwise I couldn't insert the table.

    Maybe this data will seem controversial to someone, but I was based primarily on the recommendations of tire manufacturers and the load values ​​\u200b\u200bdeveloped by them. The only thing that may seem inconvenient with this approach is the fact that when the car is loaded to the maximum or when driving conditions change, your tires will have to be adjusted to the desired value in accordance with the table.

    R to summarize, you can add
    !!! increase the pressure from the nominal (according to the table) by 0.3-0.5 atm is necessary: ​​
    - before driving long distances on the highway;
    - before the carriage of goods;
    - before driving in mountainous areas with an abundance of stones, rubble. Keep in mind that an overinflated wheel rolls over an obstacle more easily and heats up less

    !!! it is necessary to reduce the pressure from the nominal one:
    - before driving on unsteady, slippery soils and wetlands;
    - before driving on the sands;
    - before driving on loose snow or ice.

    P With a decrease in pressure by 30-40%, the contact patch increases, which increases traction, improves self-cleaning of the tread, and, accordingly, patency. However, on tubeless tires, you need to do this with a cool head, the minimum threshold lies somewhere in the range of 1.0 - 1.5 atm, depending on the size of the tire, the weight of the car, the design of the tire itself and even the disk, and most importantly your experience. Otherwise, the wheel can be disassembled, and the problems will immediately move to a different plane. But if you insert a chamber into the wheel, then you can even reduce the pressure to 0.5 atm. In this case, you need to make sure that small foreign objects do not get between the disk and the tire, which can damage the camera. Long off-road driving at especially low pressure is only possible on specially equipped wheels or with special tires. As a rule, bias-ply tires are easier to ride at low pressure due to the stiffer sidewall, and sometimes the change in pressure per unit is not very noticeable to the eye.

    When driving at reduced pressure, remember the basic rules:
    - speed should not exceed 30-40 km;
    - it is necessary to move smoothly, in "tightness", especially when hitting stones and large objects, so as not to disassemble the wheels;
    - be careful on bends when there are high side loads, try to keep the turning radius as large as possible and avoid bumps and hits of the sidewall on the edge of the track;
    - be especially careful on steep descents and ascents.

    Technical atmosphere (AT or AT) = KGS/cm 2 (BAR), Bar (PSI) Fund-WiLi for inch (ATM), physical physical Atmosphere kPa (KPA), kilopascal
    Technical atmosphere (AT or AT) = KGS/cm2 - 0.98065 14,223 900EALL , bar 1,0197 - 14.504 0.98692 100
    (PSI) Pound -WIMS 0.07030 900 0.068948 0.068948 9 - 6.894745
    (ATM), Physical atmosphere 1.033 1.01325 14.696 -

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