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Tire pressure changes

chrismpero

chrismpero

Guest
Guest
Hello all!

As we know pressure changes with temp. Cold is loses, warm it raises..
My question is how much do people usually see their pressure rise throughout the year when riding?  During the summer months if i set mine to 42 cold they'll usually go up to 43-44 according to the display.  This morning is was brisk at around 53 degrees and the pressures were 39 in the Front and 40 Rear. During my 45 mile slab commute today they barely raised at all. 
 
IMO, your starting ( cold ) tire pressures are too high.
Drop them a pound at a time till you see a 10% rise
in pressure from a warmed up tire.
 
Or follow the manual and continue to set the pressure at 42psi for best tire wear/handling/load carrying capability.
 
Right or wrong this is what I do. Mid 40s in the A.M.here and seeing my pressure drop. I just pup up to 42 cold.


Phil said:
Or follow the manual and continue to set the pressure at 42psi for best tire wear/handling/load carrying capability.
Click to expand...
 
I employ the ideal gas law when setting tire pressure. So tire pressure setting is based on ambient temperature, with 42 psi at 65 degrees as reference point. There is approximately a 1 psi difference for every 10 degree change in ambient temperature for psi's around 40. Assuming tires are "cold" = ambient temperature, if 85 degrees when checking tire pressure, I set tire pressure to 44 psi (equivalent to 42 psi at 65 degrees). If 45 degrees, I set to 40 psi.

https://en.wikipedia.org/wiki/Cold_inflation_pressure
 
Texas Concours14 said:
I employ the ideal gas law when setting tire pressure. So tire pressure setting is based on ambient temperature, with 42 psi at 65 degrees as reference point. There is approximately a 1 psi difference for every 10 degree change in ambient temperature for psi's around 40. Assuming tires are "cold" = ambient temperature, if 85 degrees when checking tire pressure, I set tire pressure to 44 psi (equivalent to 42 psi at 65 degrees). If 45 degrees, I set to 40 psi.

https://en.wikipedia.org/wiki/Cold_inflation_pressure
Click to expand...

This is the reason for all the different TPMS readings some get. If I'm not mistaken the sensors are calculated at  68*. So if you fill your tires with the ambient temperature at 68* degrees your dash readings should match up to gauge.
 
The more moisture in the air in the tire the bigger the affect temperature has on pressure as well.
 
My Zumo has a tire pressure monitor app and I bought a set of the Garmin sensors for my Ducati because I have come to rely on the TPS feature. They work differently than the Concours units as they don't have the temperature compensating feature. I tried them on my Concours and compared. The Concours units will increase by 1 or 2 PSI as the tires reach operating temperature. In contrast the Garmin units will increase by 4-6 psi.

 
I have the Garmin units as well.  Clearly shows how the pressure rises as the tires warm up.  Note that starting out they match the C-14 pressures when the temp is around 70, and then the Garmin sensors tend to read higher since they are not temperature compensated. 

Front
Tirepressfront.jpg


Rear
Tirepressrear.jpg
 
My TPMS gauge increases 2 psi during most rides. 
I prefer my Avon tires pumped harder cold than sidewall says, so ~ 44 for front.
 
4Bikes said:
The ambient temperature has a say in how the TPMS reports the pressure.  See the chart in this link.  I still swear by this method of checking and filling the tires.  My tire pressures are consistent year round.

http://forum.cog-online.org/index.php?topic=45577.0
Click to expand...

Ssdly, this is an example of "knowing" physics, but applying it incorrectly. You aim is not to "match the reading of the TPMS," but rather to have the correct PSI in the tire at the ambient temperature, which for the C14, is 42 PSI. All physics tells us is that if you set the pressure to 42 psi at 100 degrees, and then the temperature drops, the tire pressure will drop, meaning you will have to add air to bring it to the correct psi once again.

I have seen this chart pass around for years, and it really bothers me. I respect Fred, but he is so wrong about this, and any tire guy will tell you the same. I once emailed Michelin and asked about this, sending them the chart and Fred's information, a nd they were dumbstruck, and reiterated that you are to fill the tire to the manufacturer's recommended psi, at the current ambient temperature. I wish I could find the email now, but I couldn't.

What is really disturbing about it, is as the temperature lowers, the chart tells you to lower the pressure, and if you ride when it is really cold, as I do, you will have dangerously low pressures in your tires.

I truly believe that many of the people who complain about bad tire life, are following this bad advice. All I know is I follow the manufacturer's recommendation, and get great tire life. I got over 10,000 miles out of the stock Bridgestones. My rear PR4 has at least that on it right now.
 
C-14 riders may be unique. We have the option to ride with the TPMS display showing. If you follow my advice and the chart, you will see the same pressures on the display all year round. My tires last as long as the tar and chip roads and throttle hand will allow.  :motonoises:  :-\

The worst thing I believe we will agree on is not checking your tires or knowing they are not inflated properly for weeks and months.
 
I agree with 4Bikes... Tires last as long as the tar and chip roads and throttle hand will allow. 
The worst thing I believe we will agree on is not checking your tires or knowing they are not inflated properly for weeks and months.
  (please don't tell anyone I sed that) 
                      :iagree: :sign0098:

Everyone keeps talking about change in ambient temp causing pressure changes.
Here {South Texas} the ambient remains pretty consistent. {ie:"HOT"}
What causes the pressure changes is primarily the hot roads, friction from rolling/turns/braking, and the heat generated by the brakes.

Ride safe, Ted
 
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