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Comment by tmh88j | Hacker News Reader

> Charging customers for nitrogen filled tires that contain no more nitrogen than air (hey 78% is a lot!)

Are dealerships claiming to use nitrogen and just pumping in regular air, or are you talking about the unnecessary upselling of it? It's common in racing to use nitrogen, but yea, totally unnecessary for a Camry or whatever. One of my cars displays a warning telling me to visit the dealer when the tire pressure is low because the manufacturer recommends using nitrogen. I laughed the first time I saw the message on my gauge cluster before I knew the reason...still a ridiculous thought going to the dealer to top off my tire pressure even for nitrogen.

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I had forgotten that this was done in racing but can't imagine why you would want this for a commuter vehicle. I assumed they were just adding a line item to the bill and nitrogen made it sound more legit. But now that you mention it maybe they were offering to fill the tires with nitrogen like in the race cars but then just using regular air because really how would the customer know?

The argument is that Nitrogen would have lower moisture content than air, and that allegedly reduces corrosion in the tires and wheels.

Also Nitrogen filled tires lose pressure more slowly, because Nitrogen molecules are larger. The difference is not significant.

> Nitrogen molecules are larger.

That's what they told me at the dealership too. I asked "larger than what? Air is a mixture that's already 78% nitrogen." Didn't get an answer.

As far as the lower moisture content, couldn't they pass the air through an air dryer before filling the tire if it was that much of an issue? Regardless, the outside of the tires & wheels are exposed to far more corrosive materials.

>That's what they told me at the dealership too. I asked "larger than what? Air is a mixture that's already 78% nitrogen." Didn't get an answer.

No idea about molecule size, but the reason for nitrogen is that it expands less than air when heated, so tire pressure doesn't change as much when driving hard on a track.

> As far as the lower moisture content, couldn't they pass the air through an air dryer before filling the tire if it was that much of an issue?

Yes, this point is some dealership BS. Pretty much every auto shop will have a dedicated air line for filling tires, if not the whole system with an air dryer.

When I was a pro mechanic, the whole compressed air system had moisture removal, because I don't want that shit in my air tools, either. I don't know about Costco, but of the shops I know of, it's one big compressor for tools, tires, etc.

> >That's what they told me at the dealership too. I asked "larger than what? Air is a mixture that's already 78% nitrogen." Didn't get an answer.

> No idea about molecule size, but the reason for nitrogen is that it expands less than air when heated, so tire pressure doesn't change as much when driving hard on a track.

Pressure/temperature/volume for any gas are governed by the ideal gas law, which doesn't care what your molecules are.

(Sure, it's an approximation, but certainly one that's imperceptibly reliable enough for car tyres).

> totally unnecessary for a Camry or whatever.

Forget the Camry, it's hard to construct a road use application that actually makes sense. I guess you can be a bit more relaxed about checking during seasonal changes....

> Forget the Camry, it's hard to construct a road use application that actually makes sense.

For daily driving, sure, but a lot of people track their cars. I don't care about nitrogen in my tires because I'm hardly a competitive racer or frequent track-goer, but for owners of "from the factory" track cars like the ZL1 1LE or GT3 RS I'm sure it matters more to them.

As I said, "road use". Applies to most track days too, really. Maybe if you are club racer with a dedicated (i.e. trailored) track vehicle.

Right, I meant that people often track their street cars. I've already said that I don't bother with nitrogen, but it takes a special kind of person to run R compound tires on the street...

Sure but people that track their street cars are rarely seeing any real benefit from nitrogen, either. It's a pretty marginal thing. Vast majority of people going to track days hit their own limits well before getting anywhere near the equipment limits.

The use case is that once given bigger air molecules, customers will come back to the shop to top off on said molecules.

That gives the parts guy the ability to peddle $75 windshield wipers and gives the sales manager an opportunity to pitch the customer to buy/sell the car.

For Costco, it’s perceived value. “Wow, I get my magic air and aren’t spending $300 every time it fill it!”

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