Did you know: Tire Pressures When Adding Larger Than OEM Tires
Knowing what tire pressure you should be running in your OEM size tires is easy. The manufacturer gives you this exact data on a placard which is usually attached to the driver's door or door jam. It shows the two primary data points used to determine what pressure to run. These are, of course, the tire size, and the vehicle GVRW (load). From this, they have calculated the proper tire pressure. You should follow always this recommendation for on-pavement driving.
However, the door jam information is only valid for the original tire size and vehicle weight listed on it.
This is where the problems start for many. For off-roading and even just for looks, we often upgrade to substantially larger tires than those originally provided by the vehicle manufacturer. This generally leads to what, for many, is a very confusing question. "What tire pressure should I run in my new, much larger, tires?
So just how do you decide what the appropriate pressure is for your new tires? Let's examine that a little.
Maximum Load and Inflation on tire
I will start with a few ways NOT to determine the pressure for your larger tire size. These are what I often see as common answers, online when some ask for help with this question:
Some say: ALWAYS USE WHAT IS ON THE DOOR PLACARD REGARDLESS OF TIRE SIZE. ~
It is common to see some claim you should "ALWAYS" use the tire pressure shown door placard. That makes no sense if you think about it for a moment. If you think you should use ONLY the air pressure shown there, why would you not also ONLY use the tire size show there? Both are on the exact same data placard. The placard shows the tire size and pressure together because that is the pressure, for THAT specific tire, on that specific vehicle. You will find the GVRW (or max. load) is shown, on the same placard, because that is a part of the data used to determine the appropriate tire pressure for YOUR tires on YOUR vehicle.
So, unless you have that same (of very similarly sized) tires, that is not an appropriate answer to our question.
Many others say: USE THE PRESSURE PRINTED ON THE TIRE. ~
Another common claim is that you should always use the pressure that is printed on (or molded into) the tire's sidewall. For almost all of us in the off-highway vehicle community, that is going to be WAY, WAY, off. What you will find there are two pieces of information. These are the MAXIMUM PRESSURE and the MAXIMUM LOAD. These numbers are specific to each other and are always printed next to each other for a reason. They indicate the maximum safe load (max. vehicle weight or GVRW) when at the tire's maximum safe pressure. It is not just me saying this. The Goodyear Tire And Rubber Company remind us on their website: "The recommended PSI should not be confused with the maximum cold inflation pressure that the tire is rated to hold, which is found on the sidewall." The only time you should be at the maximum pressure on the tire is when your vehicle is at the maximum safe load on the tire. Just to be clear, "maximum" and "recommended" are in NO WAY synonymous.
Definitionof: maximum - max·i·mum | \ ˈmak-s(ə-)məm \1: the greatest quantity or value attainable or attained2: an upper limit allowed (as by a legal authority) or allowable (as by the circumstances of a particular case)
So what is printed on the tire is NOT the correct answer to our question.
Now for some information on what does work.
The Interco Tire Corporations says: "The “Chalk” method is a no-tech life hack that is commonly used by those who run larger off-road tires to determine PSI for pavement pounding (Highway Speed Driving). The “Chalk” method easily indicates if your tire’s tread has too much of an arc (convex shape of the tread) from too much pressure, or if it is slightly concave from a lack of pressure."
Many people use this method for its ease and because it requires little more than some chalk, a flat area to drive a few hundred feet, and a tire pressure gauge. You should know that setting too low a pressure can be very dangerous and a chalk test, when done incorrectly, has been known to cause some people to set their pressure at an unsafe level. Make sure you understand how this method works before utilizing it.
To read more about this method, go to Interco's website by clicking here: Itercotire . Please pay special attention to their warning on low pressures. There are also many Youtube videos concerning the Chalk Test.
35x12.5x17 Load/Inflation Chart
USE THE TRA OR MANUFACTURER'S LOAD AND INFLATION TABLES: The Tire and Rim Association, which is the technical standardizing body of the tire, rim, valve, and allied part manufacturers for the United States, sets and publishes manufacturing standards for all technical aspects concerning, among other things, tires. This includes recommended tire loads and pressures. These charts come from the engineers that set the standards for your tires to start with.
Finding a manufacturer's Load And Inflation Table can be tough though. Toyo and Bridgestone share theirs on their online pages but many do not. However, almost all of the major tire brands have a customer help phone line where you can ask this question. If you call, give your vehicle make/model or GVRW, and they will give tell you what the proper tire pressure is for your combination of vehicle and tire.
A great resource for looking up this information for yourself is, tirepressure.com. There you can look up appropriate pressures in several ways. The most useful, for our purposes, are the "Tire Pressure By Tire Model" and the "Tire Pressure By Tire Size" charts. The site has specific tire brand & model charts for 26 of the top tire brands (628 different models) sold in the United States. If your tire is not on the model-specific chart, THEN use the tire size-specific chart. Always look for the brand/model chart first.
OEM JEEP JKU RUBICON TIRE
Remember, when using these charts, the loads shown are based on what load each tire carries. So, for most of us in off-road SUVs, we will divide the GVRW of our vehicle by the number of tires on the ground, to ascertain an individual tire's load. For example, my JKU Rubicon, with accessories, is 6100 pounds. 6100 pounds divided by 4 tires give me 1525 pounds of load on each tire. So, I require enough pressure to carry that load. (Note: Pick-up trucks often use different front tire and rear tire pressures due to the large payloads involved. This requires different calculations than simply dividing by 4.) DO NOT use a lower pressure or a higher pressure than the charts show for a tire or tire size. These charts tell me I can safely run 25 pounds of pressure in my tires. However, I have found 28 pounds works best for my vehicle/tire/rim combination. You may want to tweak your pressures slightly, for your combination, too.
A related method, which uses these same industry load and inflation tables, compares the load and inflation information for your OEM tires and seeks to set the same load-carrying capability in your new tire size. You do this by looking up your original tire (or tire size) and the load-carrying capacity based upon your OEM tire information. You then compare that load-carrying capacity to that of the new tire/size. This can be a better method for those vehicles (like pick-up trucks) that specify different front and rear tire pressures as you can easily figure these separately. A handy aid in doing this is the "Calculate New Tire Pressure" feature on Tiresize.com (https://tiresize.com/pressure-calculator/).
So now you know some answers to ignore and several methods for getting a correct answer to "what pressure for my new tires". Use the links for more information and the industry's Load and Inflation Tables. Hopefully, this has helped a little bit with one of those questions which seem to set the internet off.
(NOTE. This article is posted for your reference only. Underinflated and overinflated tires can both be very dangerous at highway speeds or just on pavement.) Select your air pressure carefully.