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Tire Pressure And Barometric Pressure


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So I'm thinking about the tire pressure (being nerdy again trying to work through the mental exercise), that's it's not really an absolute value (right?) that it's a relative value. We have 1ATM (29.92"Hg at sea level) pressing on the outside of the tire and the air that we put in is pressing back at whatever pressure we set as measured on our tire gauge.

 

If we set the pressure on Monday and Tuesday a weather system moves in with it's associated barometric low, will we need to change our tire pressure? Any why?

 

But my real question is why does the bike manufacturer recommend a tire pressure, then the tire manufacturer says to run a specific pressure, then when you arrive at the track, the local hero says to run another number that's always lower than either. Do the manufacturers not know what they're talking about?

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So I'm thinking about the tire pressure (being nerdy again trying to work through the mental exercise), that's it's not really an absolute value (right?) that it's a relative value. We have 1ATM (29.92"Hg at sea level) pressing on the outside of the tire and the air that we put in is pressing back at whatever pressure we set as measured on our tire gauge.

 

If we set the pressure on Monday and Tuesday a weather system moves in with it's associated barometric low, will we need to change our tire pressure? Any why?

 

But my real question is why does the bike manufacturer recommend a tire pressure, then the tire manufacturer says to run a specific pressure, then when you arrive at the track, the local hero says to run another number that's always lower than either. Do the manufacturers not know what they're talking about?

Some of it is legalities. The manufacturer picks a safe range where the tire will last and traction OK. Most tire manufacturers will list a value but say run whats in owners manual (covers there butt).

 

Local hero "may" know the best pressure for that track/tire/temp.

 

I track marshal for MotoAmerica (and also did the World Superbike at Laguna Seca this year) and have had several good discussions with the Dunlop tire techs. They are more willing to tell in in discussions whats best as its not written so they are not held liable.

 

Sad it has to be that way, but thats our society.

 

I set my tires pressure before each ride (cold) as it gives me a good baseline.

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The manufacturer has to factor in all intended use cases. From the slow guy to the fast guy.

 

The pressure variances that you will see with the "super low pressures" are heat related. The more friction and temperature a tire a tire see's during use causes the pressure inside to grow. The fast guys lower the pressure because even off the warmers their tires will heat up and the pressure will grow. There's a black art to this that I don't fully understand yet but find yourself a fast guy who understands it and you will get some "magic numbers" that will work well for your tires. Be sure to make sure he understands your pace otherwise he will recommend the pressure for his pace which might not work as well for you.

 

I run my Pirelli SC2 slicks at 34/26-27. Slightly higher pressures in low temps and slightly lower in hot temps. The fast guys run theirs at 34/24-26.

 

Utilizing tire warmers accomplishes the following for any rider.

 

1. Gets your tire, carcass and wheel as hot as possible so that they remain hot throughout your session.

2. Allows you to set a more accurate hot pressure.

3. Eliminates doubt that can rent space in your head and slow you down (are my tires hot enough?)

4. Provides a margin of safety by preventing cold tires.

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