Nitrogen in tires
Here’s a question I received recently about nitrogen in tires:
Is there a way to verify the tires on my trailer have been inflated with nitrogen? My tire dealer said they did, but I am not sure if I can trust them. The pressures stay even tire to tire and not a lot of change while driving, which I think tells me that the tires are inflated with nitrogen.
My answer
As a Tire Design Engineer, I see no reason to worry about the claimed use of nitrogen. The air we breathe is 78% nitrogen. While using N2 to inflate tires is not bad, in my opinion it just isn’t worth spending any money on it. Even if the tire dealer offers to “Top Off” your tires a couple times a year, it still costs you time and fuel to drive to the dealer.
Inflation
About your question on inflation: Are you using a TPMS (tire pressure monitoring system) to monitor tire pressure, or are you using a hand gauge? I do not know how accurate your pressure readings are when using a hand gauge. If you pay attention, you will hear a little “Pfft” every time you use a hand gauge. Even if you somehow manage to get the gauge on the end of the valve stem quickly, there is always a little leakage.
TPMS are generally accurate to +/- 2%, and they can warn of a puncture while driving down the road. I have seen a tire fail because the owner used his hand gauge but the valve core stuck slightly open. The tire failed 50 miles down the road after doing a pressure check. This is a reminder that if you do not use a TPMS, you should always cap the metal valve stem with a cap to seal the air in the tire.
Finally, I have heard the claims about nitrogen-inflated tires never changing pressure. The problem with this claim is that all gases follow the same physics and obey the “Gas Law of PV=nRT.” [The ideal gas law is summarized by the equation PV = nRT, which relates the pressure, volume, temperature, and amount of a gas under ideal conditions.]
Here is a post of my inspection of that tire. I believe that if he had been running a TPMS he would have avoided that failure.
Replacing OEM tires
I received this question on LT225/75R16E versus 225/75R16 Commercial tires:
I’m looking to replace tires on an E-450 chassis motorhome. The OEM tire is an LT225/75R16E. Reading the forums, I see a number of people are replacing the OEM tires with 225/75R16 Commercial rated tires. They are doing this because the OEM Load Capacity is very close to the sum of the load of the four E rated tires. Four Commercial tires adds approximately 500 lbs. per tire load capacity, or 2000 lbs. for four tires.
My research has turned up seven tires that have both an E rated and Commercial in the same model tire. What I found and surprised me was the weight difference between the two tires. With the exception of one brand, all show that the Commercial rated tire weighed less than the LT E rated tire. As a lay person, it seems counterintuitive to me. While there are other tires, here are two tires, and their advertised tire weight, I am considering:
Michelin Agilis CrossClimate
Commercial: 37 lbs.
LT E rated: 39 lbs.
Toyo Celsius Cargo
Commercial: 36 lbs.
LT E rated: 38 lbs.
I would have thought the Commercial tire would have been heavier given that the Commercial tire has approximately 18% more load capacity. Can you explain and shed some light on this? Thanks.
My answer
We need to be careful when comparing tires as the actual “TYPE” and Load Range can result in our selection. The Michelin Agilis is a good example. This is a tire developed in Europe and it does not carry the “LT” designation. In Europe they call some lines “Commercial” and other tires of the same size are not considered “Commercial”. The Load Index number is the tip off. You can consider this a bit like the “Load Range” aka “Ply Rating” in the U.S. market.
The additional load capacity differences come about because of the conversion of Metric to “English” dimensions. I think that if you look at the actual specifications for the tires you are looking at, you will find the stated inflation numbers are slightly different—close but different. The expected usage can also result in some tires being considered “Commercial” versus “RV”.
Incomplete tire designations in posts
I see many people asking about or posting information on tires but they do not include the “complete” designation in their internet posts. Some include the ST or the LT on U.S. sizes. European tire sizes do not have “ST” type tires or “LT” as leading letters, but have a “C” after the rim diameter standing for “Commercial”. (Not to be confused with Load Range C.)
To further confuse the issue, some tires are available with two different Maximum Inflations and different Maximum Load Capacities.
For your question, I would suggest you look at the Maximum Load Capacity and the inflation necessary to support that load. If the inflation is higher than that shown on your Certification Label, which I think might show an LT-type tire in Load Range E and 80 psi, your “Commercial grade” European tire may specify inflation a bit higher than 80 psi. If so, you need to confirm the max inflation rating for the new tires.
I would not be concerned with the weight of the tires you are considering, as design and wear goals can add or subtract a couple of pounds per tire.
Roger Marble
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Roger, I agree with pretty much everything you’ve said but there’s a reason nitrogen is used in race cars whose tires can see elevated temperatures.
Not only is nitrogen less corrosive but due to the size of its molecules, it has a lower permeation meaning it’s less likely to lose pressure “leaking” through the rubber. Add heat from brakes and road friction combined with flexing and the benefit of lower permeation grows.
Critical in an RV with TPMS? No.
Critical in a Formula One without TPMS, crew chiefs think so.
More info for some light Sunday reading
If naysayers are adamant about not using nitrogen in tires then ask yourself why NASCAR drivers use it in their tires. I believe in the stuff as I think it helps with tire longevity…just don’t ask any Les Schwab tire dealer to use it…they will argue until the cows come home.
You and VInce (below) make good points. Racers, however, do not spend hour after hour hitting pot holes, crunching curbs, or stop and go traffic. True, their cornering and other race specific occurrences are unlike anything we RV’ers will ever experience, so nitrogen might make sense. Other than those differences I see no need to fill my tires with nitrogen. If I need to add ‘air’ to my tires and I’m not at Costco, I just pump in any air I can find – and life is good.
As I recall, Roger has a racing background in addition to the engineering vocation. What say you Roger?
Yes I raced sports cars for a number of years on tracks such as Riverside and the “road course” at Daytona. After working my way up the ranks I managed to “land” some serious sponsorship when running my IROC Camaro. I did set some lap records for cars in my “class” at a number of tracks like Lime Rock & Mid-Ohio. Was even able to lead my team to 6 consecutive class wins at the 24 hours of Nelson Ledges in Ohio. I have a picture of the car on my RV Tire Blog at Can’t “Balance” your tires? Bad ride? Info related to the Nitrogen inflation question. I only used N2 for tire inflation about half the time (when it was convenient) I never saw a measurable performance advantage.
Filling tires with nitrogen is a waste of money if they are going to charge you for that “benefit”. What you should be asking is if the tire store or gas station where you are putting air in your tires is, do you have an air dryer on your air compressor? Moisture inside the tire will cause more damage than air will.
The next question is, how good is your air pressure gauge? People talk about racers using nitrogen but even race cars have lost tires because of improper tire pressure because of a faulty tire pressure gauge.
How do you get all of the oxygen and argon out of the tire? Suck a vacuum and then fill with nitrogen? Lol.
No need for Nitrogen in automotive use. Nothing more than dealer add-on that they have maybe $2.00 in and charge you $150.00, total rip-off. I would bet good money that 75% of cars on the lot listed as having Nitrogen, actually don’t. Large commercial and military aircraft – yes, it does have a benefit.
Thank you, Roger! Have a great weekend and safe travels!