Car Advice

Should I put nitrogen in my tyres – Definitive answer

Should I put nitrogen in my tyres? Here’s everything you could ever want to know about nitrogen and tyres – the facts, the half-truths and the lies.

If you want the short answer, here it is – the benefits of nitrogen aren’t worth the cost and effort for roadcars.

Almost all of the claimed advantages of nitrogen for roadcars relate to running the correct pressure and how nitrogen makes that easier through reducing pressure loss over time, not specifically the use of nitrogen.  However, the answer is different for racecars and perhaps trucks. Now for the detail.

All about nitrogen in car tyres

Air is 78% nitrogen, 21% oxygen, 0.9% argon and 0.1% other gases.  So air is already pretty much nitrogen, which means 100% nitrogen is only adding another 22% of nitrogen into your tyres.  But there has to be some advantage for the likes of Formula 1 and NASCAR to use nitrogen or gases other than air, and the reason is precise maintenance of the desired tyre pressure. 

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In any form of motorsport tyres are one of the biggest factors in performance, and at the top level you’re certainly looking at hundredths of a second if not thousandths between cars – just take a look at the qualifying results.  Then multiply that over a race distance and you have an appreciable gap.

So tyre are critically important to performance, yet race tyres perform best within a narrow range of pressures.  You might think you could just set the pressures and be done with it, but that ignores heat.  The microscopic air molecules you’re breathing now aren’t static, they’re whizzing around at around 1800km/h. Luckily they’re very tiny otherwise that’d hurt.  An air compressor stuffs more molecules inside a tyre, so there’s more of that whizzing going on and that’s where the pressure comes from, all those molecules banging off each other trying to get out of the tyre. 

As tyres heat up the molecules of gas inside the tyre absorb energy and so they move even faster, increasing the tyre pressure.  If you measure your car’s tyre pressure first thing in the morning and then go for a half-hour drive you’ll see a difference due to heat.  The heat comes from several sources; the tyre has a flat spot where it touches the ground and thus has to deform and reform as it rotates, a process which generates heat.  The energy to do that comes from the engine, and the less deformation there is, the less energy required which is why high tyre pressures are good for fuel economy.  The tyre’s temperature is also increased when you corner, brake or accelerate as the tyre slips slightly relative to the road and that friction also creates heat.  Then there’s the warmth from the engine, shock absorbers and especially the brakes which radiate significant amounts of heat. Don’t touch the pads after a hard drive unless you want a burnt finger! 

So for all these reasons the tyre temperate increases as you drive, and with it the pressure.   There’s even a difference if the sun comes up and warms the tyre.  That’s something for offroaders in the desert – if you’re cruising over dunes at say 15psi on a warm afternoon when you wake up in the cold morning your tyres will look almost flat and be a lot less than 15.  Not to worry, the heat of the day will soon excite those air molecules and so too will the tyre movement.

Back to racing.  The race teams precisely map the expected tyre temperature and thus pressure increase from cold to warm, and set their cold pressures accordingly.  Some race series, such as F1, even go to the extent of warming their tyres before they are put on the car which means the tyres are closer to operating temperature (pressure) from the first wheel revolution, so the driver can go quicker from the start and there’s less tyre wear at sub-optimum pressures. It also means a consistent start point for their model showing the increase in pressure from ‘cold’ to optimum as the car starts off on its laps.

Now we get to the reason why these teams use nitrogen.  Air is 22% oxygen, and unfortunately the oxygen in air contains water vapour.  When water vapour is heated it too increases in pressure, but somewhat unpredictably, which means the teams cannot quite determine precisely what pressure their tyres will get to at race pace, and given the narrow range of optimal pressures that is a problem. Therefore, the teams use gases that eliminate water vapour as far as possible, such as specially dried air or  nitrogen.  This means the tyre’s temperature increase and thus pressure increase is stable and predictable.  Even 0.5psi can make a difference to a racecar.

For roadcars the situation is the same, but nowhere near as critical.  A racecar tyre’s optimal temperature is around 100 degrees Celsius.  Yes, that’s water boiling point, so there’s a massive difference between ‘cold’ and operating temperature.  A roadcar doesn’t get to anywhere near that difference between cold and operating.  A racecar tyre has a narrow optimal pressure range, not so a car tyre which is far more tolerant to pressure ranges – you wouldn’t notice that 0.5psi difference.   A roadcar’s load also changes dramatically as people and cargo are loaded and unloaded, and so its tyres are designed for a relatively wide pressure operating range.  You hear racecar drivers complaining about another 5-10kg and how much of a difference it makes.  Not something you’d notice in a roadcar.

Nitrogen doesn’t support combustion so it is safer than air, which has oxygen that does support combustion.  At a racecar’s tyre temperature of 100 degrees clearly combustion of something or other is a risk, therefore nitrogen is safer.  That’s not a problem with roadcars which have far, far lower operating temperatures.  Nitrogen is also used in large aircraft tyres for much the same reasons.

The water vapour in air can also cause rust.  A tyre contains air under pressure, which is trying to escape through the tyre and will do so, slowly, over time.  As those oxygen molecules pass through the tyre the claim is they rust the rim and the steel belts inside a modern radial tyre.  Well, rims these days are usually alloy for which rust is not a problem, and they are exposed to water and air anyway never mind any internal air leakage.  The point about the steel belts is one of those things where it’s technically true but makes so little difference to roadcars it isn’t a problem and you’d have worn the tyre out long, long before you need be even remotely concerned about damage to the steel belts.  Or the tye will have aged and need replacement after a few years anyway, regardless of tread wear.

It is also true that oxygen can damage the tyre’s innerliner, the membrane which provides an airtight seal inside the tyre.  Well, refer above for the comments on tyre life. You’ll note that no roadcar manufacturer requires their tyres to be filled with anything other than air, even for the most high-performance cars.

The claims made for nitrogen in tyres

Let’s look at the claims made for filling roadcar tyres with nitrogen:

  1. Extended tyre life;
  2. Increased levels of safety and handling;
  3. Improved fuel economy; and
  4. Increased retreadability.

Points 1 to 3 are down to running the correct pressures, not specifically the use of nitrogen and that is where the nitrogen industry is being misleading. Because nitrogen leaks out of your tyres more slowly the correct pressures are maintained for longer, but it does not mean you need not check to your pressures at all with nitrogen. Point 4 is moot for roadcars, but not for trucks as we’ll explore shortly. 

To be clear – there is no performance difference whatsoever between two identical roadcars with tyres at say 35psi, one with nitrogen and one with air, and you will not find any independent data that says there is.  You cannot feel any difference in ride or handling, and that is a fact.

Nor are you likely to find many studies showing how more slowly nitrogen tyres lose pressure than air in roadcars, and if you do, then the difference will be tiny so you’ll still need to check your tyre pressures regularly. Nitrogen fills aren’t free – around $5-$10/tyre – so you need to balance that cost with the savings expected in tyre wear, and you need to top up with nitrogen every time thereafter otherwise you begin to negate what benefits are gained. There is also no evidence use of nitrogen reduces the incidence of slow punctures.

Even if the advantages existed to a measurable degree how will your local tyre shop actually fill your tyres with nitrogen? A deflated tyre still has air it in at the ambient pressure.  Adding nitrogen to that still leaves a lot of air in there.  They could vacuum the air out, but then the tyre would implode. 

You need to fill and refill the tyre several times with nitrogen to remove all the air, and even then there’ll still be some left. Or you could do what the race teams do and use rims with two valves, one to inflate and the other to purge the air from the tyre, before that one closes and the tyre is pressurised.  The nitrogen must also be pure, and can be contaminated with air or water vapour so not all ‘nitrogen’ is equal.  Here’s the maths – the standard atmospheric pressure is 1013Mb, or around 15psi.  Let’s assume the tyre is inflated to 45psi, or three times atmospheric pressure.  Let’s also assume the nitrogen is 95% pure, 5% air, so each fill is 95 parts nitrogen, 5 parts air. 

   

Parts

  
  

Pressure

Nitrogen

Oxygen, other

Total

 

Std atmos

0

80

20

 

Fills

1

15

95

5

 
 

2

30

95

5

 
 

3

45

95

5

 
 

Total

 

365

35

400

   

91%

9%

 

Air is 80 parts nitrogen, 20 parts other.  The definition of “part” doesn’t matter, it’s the proportion that’s important.  The nitrogen is 90/5, or 95% pure.  Add up all those parts which totals 400 and then work out the percentage.  You end up with 91% nitrogen instead of 80% nitrogen, probably 90% or less if as you probably wouldn’t go to 45psi.  Not a huge difference.

Incidentally, if you really do want dry air then filling your tyres from a scuba diver’s tank is a good idea.  The air used there is highly compressed which removes the water vapour, and that reduces rust in diving cylinders and the like, and it is quality-controlled as otherwise divers would die.  The difference between a diving cylinder and a tyre is that tyres wear out a lot quicker than cylinders, and the steel within a tyre is encased in rubber, not directly open to the gas.

For offroaders the nitrogen tyre is something of a moot point as we’re always airing our tyres up and down anyway, but that doesn’t stop the industry trying to sell us the ‘benefits’.

The nitrogen equation changes a little for truck tyres.  Firstly these tyres run a much higher pressures, around 100psi compared to less than half that for road tyres.  That means the air leakage is greater – around 2psi/month according to Bridgestone.  Tests show that nitrogen can reduce than to around 2psi every six months.  The higher the pressure, the greater the rate of leakage so those figures don’t translate to 4X4s and roadcars.  The higher pressure also means that inflating a tyre from ambient pressure to operating pressure means you’ll get more gas in there, so less need to somehow remove the air from the tyre before filling it with nitrogen.  Finally, trucks have many tyres which are time-consuming to check and inflate, and time is money in the trucking business.  Cars have only four tyres and checks are much quicker.  Trucks also use retread carcasses, so the issue of preserving the carcass by not letting air molecules through it is important for trucks as the carcass will be in use for far longer.  Not so for cars which don’t run retreads.  Therefore, nitrogen may be cost-effective for trucks, although I’d weigh up the investment against the benefits of a central tyre inflation system.  Here’s the maths for truck tyres, which comes out to 93% nitrogen after 7 atmospheres:

   

Parts

  
  

Pressure

Nitrogen

Oxygen, other

Total

 

Std atmos

0

80

20

 

Fills

1

15

95

5

 
 

2

30

95

5

 
 

3

45

95

5

 
 

4

60

95

5

 
 

5

75

95

5

 
 

6

90

95

5

 
 

7

105

95

5

 
 

Total

 

745

55

800

   

93%

7%

 

The bottom line on nitrogen in tyres

If you really care about your tyres just do the usuals; rotate them every 10,000km, check the pressures at least once a month, have alignments done every other service, keep an eye out for unusual wear patterns and don’t worry about nitrogen.

Other views

We welcome any rebuttal of this article from vendors of nitrogen.


Robert Pepper

Robert Pepper

Robert Pepper is a motoring journalist, offroad driver trainer and photographer interested in anything with wings, sails or wheels. He is the author of four books on offroading, and owns a modified Ford Ranger PX which he uses for offroad touring. His other car is a Toyota 86 which exists purely to drive in circles on racetracks, and that's when he isn't racing his Nissan Pulsar. Visit his website: www.l2sfbc.com or follow him on Facebook https://www.facebook.com/RobertPepperJourno/ or buy his new ebook!