MTFCA Forum

I noticed that driving on the current hot black top my tyre pressure has increased. Is this normal?

Most definitely. It may increase by several pounds. Experts warn NOT to bleed off the increased pressure, assuming the pressure was correct to start with.

It's completely normal to have your tires increase pressure in the summertime. That's one of the reasons why a lot of high speed Jets and high performance Vehicles use nitrogen instead of regular air in tires.

The heading of this topic reminded me of this great heavy Sentinel Steam 'Lorry' as they call them in England

Here is a brief history lesson. In the 1820's, Scottish Engineer John McAdam pioneered a roadbed using crushed stone placed with a crown in the center for drainage. These are still referred as Macadam roads. Later, tar or oil was added to the mix. That was the basis of the name tarmac.

Law of physics, increase in temperature increases pressure. Always check tire pressure when they are cold.

And the Pressure-Volume-Temperature relationship for Nitrogen is essentially identical to 'regular air'.

Nitrogen is purported to escape more slowly from tires than does air. That might be an advantage with some of today's repro tubes which do not hold air very well.

If nitrogen does not expand about the same way as air when heated, higher "cold" tire pressure might be needed.
I don't know if it does or not, but nitrogen gas is a significant portion of "air".

Humblej wrote: ↑

Thu Jun 20, 2024 8:57 am

Law of physics, increase in temperature increases pressure. Always check tire pressure when they are cold.

And check it when it IS cold...meaning outdoor temp. I keep my F150 in a well insulated garage that seldom gets below 32 inside. One day in Jan '18 when it was minus 4 degrees air temp outside I only got about 8 miles from home but what the low air temp alarm on all 4 tires went off! Duuhhh I thought! Shoulda known. Do you know how PAINFUL your hands get airing up tires at the gas station in -15 degree chill factor is?!? VERY!

thermal expansion of air

Thank you all who responded. Asking a dumb question can provide interesting and useful answers.

The forum is very informative. Again Thanks.

jab35 wrote: ↑

Thu Jun 20, 2024 9:37 am

And the Pressure-Volume-Temperature relationship for Nitrogen is essentially identical to 'regular air'.

Guess What ! https://climate.nasa.gov/news/2491/10-i ... about-air/

So what is air, exactly? It's a mixture of different gases. The air in Earth's atmosphere is made up of approximately 78 percent nitrogen and 21 percent oxygen. Air also has small amounts of other gases, too, such as carbon dioxide, neon, and hydrogen.

And new cars have Nitrogen into the tires. WHY?
Since nitrogen molecules are bigger than normal air molecules, it is harder for them to leak out. This means a tire filled with nitrogen will maintain air pressure longer. Therefore, they say, you'll roll on tires that are always properly inflated, resulting in better fuel economy and longer tire life Worth it ? https://www.lesschwab.com/article/tires ... -cost.html

ALL cars have Nitrogen in their tires, from the ones filled at the tire store from fancy bottles of compressed N2 to the ones I labored so hard to fill with my ol' faithful (and exhausting) hand pump.(I huffed and I puffed and I BLEWWWWW that tire up...)

EVEN IF that 21% of non-n2 somehow mysteriously passed through the rubber barrier while the Nitrogen did not... you're only talking 1/5th of the volume. And when you refilled up your tire, your % of N2 actually INCREASES because what is remaing of your base fill of "Air" (of say24 PSI) should be pure nitrogen, so adding more N-78 (like E-85, but air instead of fuel) would increase the base % of N2 in the tire... meaning less would leak out.

Sure, people like to think it's some magical cure-all, but your great granddaddy used to fill HIS tires with about 4/5 Nitrogen, and they STILL went flat (and more than that 20% that was NOT N2). Cole surnit and Durnitall!!

What HAS changed is the overall chemistry of the rubber compounds in the tires and the quality of the construction and fabrication of wheels and rims. THAT leads to less leaks and tires hissing air in microscopic amounts, and even then, manufacturing tolerances will leave spaces for those pesky molecules to make their EEE-Scape.

I attribute tire seepage WAY less to some miracle of modern nitrogen chemistry, and MORE to the quality of Schrader valves and assemblies, and better seals between valve stems and rims.