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Tire Inflation Spreadsheet

B

BMW Triumphant

Ed Kilner #176066
This link may work and then you could download an Excel spreadsheet (use Excel or Google Sheets (free).)

https://docs.google.com/spreadsheets/d/1GMtju5P-wOhImg8GdLiv3qkBMUTnsP9e_NdsWYw2IWU/pub?output=xlsx

When open, you can input your desired inflation, say 38psi, and the current ambient temperature. You will see the calculated pressure to which you should inflate the tire.

The manufacturer's tire recommendation is valid for 20 degress C at sea level. The spreadsheet does correct for other temeratures but not altitude.

Do let me know if you encounter any difficulties accessing the spreadsheet.
 
Thanks. I have been running some studies for myself, tracking treadwear to pressure, using 1000 mile increments. I did log ambient temp at pressure, but my readings were not adjusted for these variations. I will have to go back and modify these.

John
 
BMW Triumphant said:
This link may work and then you could download an Excel spreadsheet (use Excel or Google Sheets (free).)

https://docs.google.com/spreadsheets/d/1GMtju5P-wOhImg8GdLiv3qkBMUTnsP9e_NdsWYw2IWU/pub?output=xlsx

When open, you can input your desired inflation, say 38psi, and the current ambient temperature. You will see the calculated pressure to which you should inflate the tire.

The manufacturer's tire recommendation is valid for 20 degress C at sea level. The spreadsheet does correct for other temeratures but not altitude.

Do let me know if you encounter any difficulties accessing the spreadsheet.
Click to expand...

Sorry, but I disagree. 38 psi is 38 psi no matter what temperature or elevation at which you take your reading. If your tire is designed to run at that pressure, then that is the pressure one should use. We did not alter pressure when racing in Denver versus Portland. We did alter pressures (within a range) dependent upon tire temp readings.
 
BC1100S said:
Sorry, but I disagree. 38 psi is 38 psi no matter what temperature or elevation at which you take your reading. If your tire is designed to run at that pressure, then that is the pressure one should use. We did not alter pressure when racing in Denver versus Portland. We did alter pressures (within a range) dependent upon tire temp readings.
Click to expand...

Boyle law.For a fixed amount of an ideal gas kept at a fixed temperature, pressure and volume are inversely proportional
Environmental temperature variance does make a difference.
 
pch123 said:
Boyle law.For a fixed amount of an ideal gas kept at a fixed temperature, pressure and volume are inversely proportional
Environmental temperature variance does make a difference.
Click to expand...

Sorry, you meant to reference Guy-Lussac's Law, P/T = constant when V and mass are constant
 
pch123 said:
Boyle law.For a fixed amount of an ideal gas kept at a fixed temperature, pressure and volume are inversely proportional
Environmental temperature variance does make a difference.
Click to expand...

Which simply explains why tire pressures go up after riding a few miles, since the tires heat up from flexing. But I have to agree with BC1100S. If I lower the inflation pressure when the ambient temperature is below 20 degrees C, the tire will flex more and may overheat, resulting in a warm tire pressure that's too high. The spreadsheet mimics BMW's TPMS, where displayed pressures are "corrected" to 20 degrees C. I have yet to find any other manufacturer that performs this "service."
 
kthutchinson said:
Which simply explains why tire pressures go up after riding a few miles, since the tires heat up from flexing. But I have to agree with BC1100S. If I lower the inflation pressure when the ambient temperature is below 20 degrees C, the tire will flex more and may overheat, resulting in a warm tire pressure that's too high. The spreadsheet mimics BMW's TPMS, where displayed pressures are "corrected" to 20 degrees C. I have yet to find any other manufacturer that performs this "service."
Click to expand...

Agreed. I bounced this 'spreadsheet approach' off some professional motorcycle racers with whom I work with here at Road America. They echo your sentiments about excessive attention to tire pressure algorithms (as well put by BC1100S - "38 psi is 38 psi...").

Not to mention that low tire pressures (not nails, screws, worn tread, etc.) are the Number 1 cause of tire failure - both on the street and the track.

I did appreciate the 'shout-out' to Boyle - as a professional diver in my former career (Dive Rescue Team/Team Leader, PADI Master Scuba Diver & DiveMaster), a familiar concept.

This club includes an element that enjoys a spirited discussion as they micro-focus on a plethora of minutia - oil, suspension, speedometer accuracy, nitrogen vs. air and yes - tire pressures.

There are worse things in life to fixate on, so to each their own. :dance
 
kthutchinson said:
The spreadsheet mimics BMW's TPMS, where displayed pressures are "corrected" to 20 degrees C. I have yet to find any other manufacturer that performs this "service."
Click to expand...

Correcting to "Standard Temp & Pressure" STP is typical for most electronic flow meters. In the case of a TPMS, a simple thermocouple of some sort would address the temperature issue, P_Stp = P_meas X (T_Stp / T_meas).
 
Why are some riders so OCD about tire pressure, 2-3 pounds variation from the recommended "cold" temps makes virtually no real world difference for normal riding.
 
Just sharing the spreadsheet for those who are interested in such things. If that is not you, no problem.

To my way of thinking, pressure is a surrogate measurement for the counting of molecules of air in the tire. At STP, the recommended pressure assures us of the correct amount of air in the tire. At other ambient temperatures, the spreadsheet assures us of the correct amount of air in the tire when we add air, probably because we noticed an underinflated tire.

Sure, there are tolerances, probably rather wide tolerances. My skills are not good enough to know by feel the tires are over/under inflated unless it is a lot over/under. You may have far greater skills, and I hope you have.

Just know that air expands / contracts with temperature and the same pressure at different temperatures means there is a difference in the amount of air in the tire.

Use the spreadsheet or not. Use the BMW TPMS or not. It's up to you.

And for those who said Thank You to me: you are welcome.
 
I downloaded the spreadsheet and I may use it sometimes. I just have to convert it to Kelvin.

Thank you for posting.
 
Thanks for the spreadsheet. Whether we realize it or not there is a data nerd hidden in every forum member. What makes makes the inner nerd surface varies member to member. The minutia debates are great fun to read.

I will admit my eyes glaze over after reading the the first cell. For all the discussion about temps, which law to apply I am stuck wondering about “desired”. K,C,F or any other temperature scale why is 38 or any other X temp the target? The spreadsheet looks like a fun tool but until you understand the what and why of the first cell it is just a sorta cool data generator.
 
mika said:
Thanks for the spreadsheet. Whether we realize it or not there is a data nerd hidden in every forum member. What makes makes the inner nerd surface varies member to member. The minutia debates are great fun to read.

I will admit my eyes glaze over after reading the the first cell. For all the discussion about temps, which law to apply I am stuck wondering about “desired”. K,C,F or any other temperature scale why is 38 or any other X temp the target? The spreadsheet looks like a fun tool but until you understand the what and why of the first cell it is just a sorta cool data generator.
Click to expand...

I repeat, 38psi is 38 psi. There is nothing else to know.

:laugh
 
Ed thanks for taking the time to create that. I immediately saw the value in it, as I like a consistent tire pressure as it facilitates my riding style. The only thing I would suggest is maybe running the numbers from 0-40 Celsius, as it's the extreme temps where the compensation would play a more serious role. Though I have not rode a bike in 0 or 40 I have been in those temps, and I suspect there are those who would find those temps a pleasant riding day, especially in this club.
 
BC1100S said:
I repeat, 38psi is 38 psi. There is nothing else to know.

:laugh
Click to expand...

I don't know what techno-deity you follow, but 40 front and 42 rear............is my holy gospel. It's written on the "Made in France" label on my Bagster tank cover. Source, a long lost Michelin tire vendor at an MOA rally, somewhere, in history.
 
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