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"Cold" tire pressure

flyrider

flyrider

Morning Person
What, exactly, is "cold" tire pressure. I measured my tires the other morning when it was 65 degrees before a ride. Adjusted to spec. Tonight I measured in the same garage, when it was 90 degrees out, and - as might be expected - the pressures were a couple of pounds higher.

Which pressure is right?
 
widebmw said:
Somewhere I saw a post that said that cold was 20 (c) - 68 (f) :scratch
Click to expand...

Probably about right. Just read some stuff on it and all recommend checking first thing in morning. Readings will be approximately 1 psi higher for each 10 degrees above standard cold reading in the morning.

Sorry for posting the question. Sometimes I forget about internet searching for answers. Call me a Luddite, I guess...:brow
 
Last edited:
I just installed a Tire Pressure Monitor system on my GSA.

AT 38 front and 42 back ...in the morning..temp about 70.

As expected the pressure increases with tire temps and heat of day...

At 103 degrees enroute to MOA rally ... my pressure was 42 F and 47 back...

thus 4 PSI per tire.... increase

I have always understood COLD to mean : pressure without having run the tire, therefore if you rode to nearest service station, the tire would no longer be cold.
 
Do a search here on the forums, type in "Cold tire pressure". I asked this same question back on 4-11-2012.
There are some good answers there.
 
Standards

Cold means "standard temperature and atmospheric pressure". Standard temperature is 20c (~65 f). Standard pressure is sea level.

Biggest thing is to be consistent. Use the same gauge, before you ride and understand that a host of factors come into play. MC tires don't have nearly the amount of air that car and truck tires do. The tour bus I drove showed a 20 psi difference because of sunlight on one side vs the other.

Don't obsess about fractions. Do the same measurement every time and you won't be far wrong. Hey, at least you're checking!!!:brow
 
I went to Basic and Not so basic Tech at Sedalia and according to my notes, Paul Glaves said Normal Cold Tire Pressure was 70F.
 
Cold for Paul Glaves, in Texas, might be 70F. Cold for me, in Ontario, might be 70F in summer and 40F in spring and fall. It's relative to one's surroundings. Either way, check the tires when they've not been ridden for several hours or overnight and check them regularly using the same gauge.
 
Cold does NOT mean what the temperature is where you are!

In a chemistry lab, we use Standard Temperature and Pressure as set by IUPAC (25C, 77F). But there is also NIST (20C, 68F). I didn't know about NIST until I looked at Standard Temperature and Pressure on Wikipedia.

So, I don't know if tire manufacturers mean 68 or 77, but really, it doesn't matter that much at that level.

Now, 40F is cold, and would result in a lower pressure. I don't feel like doing the math, but it would make a difference.

The point is to be consistent. Maybe I say 36psi (at 77F) is "correct" and another says 33psi (at 40F) is correct. And his 33 might be the same as my 36! And then you toss in gauge error which easily can be 2 psi.

Pick your pressure and be consistent.

Don't take a hot tire and bleed off PSI to the cold temperature.

Don't obsess over it. Instead, obsess over what oil to use!
 
Interesting discussion. I had noticed that my tires seemed to be wearing faster this year. I check tire pressure almost every time I ride and set it at 40 psi. I will sometimes make a small correction if I know it will be much warmer or colder at the end of my ride than the beginning, but I never have corrected for the ambient temperture being higher or lower than 68 F. Now that I think about it, with the really high tempertures this year and my trip to the Ozarks that was 90+ most of the time, I have probably been chronically over inflating my tires by a couple psi all summer long. And in the winter, I'm probably over inflating them when I could actually use a little more traction due to slower tire warm up time. I'll make adjustments in the future. Thanks!
 
You guys are way overcomplicating this. Cold tire pressure is the pressure in your tire before you ride your bike and warm up the tire from riding. In terms of the number you want to see on your tire gauge when you measure the tire first thing in the morning before you ride, the temperature of the air and the altitude and the humidity is irrelevant. 40 psi is 40psi regardless of the outside air temp.

Now, if you ride from a very hot place to a very cold place or vice versa, you may need to adjust tire pressures but when you do, the number of the gauge you're looking for is the same regardless. if you want 42 psi, you set it to 42 psi regardless of the outside air temp.
 
There is some truth to that. If you are riding around on a 40F day, I'd inflate my tires to the pressure I like (say, 36psi front). I wouldn't lessen the pressure due to the cold. 36psi feels like 36psi, 32psi feels like 32psi!


The only thing I'm suggesting is that if you inflate at 40F, and then the next day it is 80F, your pressure will be greater and you might find that you bleed off a few PSI in the morning.

But really, in actual practice, I don't get too crazy over it, either. I set my pressure at the beginning of a day, adding or releasing as needed each day. Almost never releasing.
 
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Tire Pressures

You don't have to ride it to raise the pressure, just park in in the sun. The pressures will increase.
 
Folks are comfusing cold tire pressure and the "cold" tire pressure specification published by BMW, and the "maximum cold pressure" embossed on the side of the tire.

In the case of the former cold is whatever it is sitting stiill for a while.

But cold pressure specifications and the maximum cold pressure specification are both at the standard temperature of 20 degrees C.
 
"Cold" pressure is ambient, without the added heat of the sun or friction from riding.

When it's 20 degrees, you inflate to the "cold" pressure.

When it's 120 degrees, you inflate to the "cold" pressure.


Use common sense if you see a big temperature swing during the day. Ditto if you're seeing drastic altitude changes.
 
RoboRider said:
You might find this interesting:

http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=73

One thing the article says is:

The rule of thumb is for every 10?? Fahrenheit change in air temperature, your tire's inflation pressure will change by about 1 psi (up with higher temperatures and down with lower).

So if you normally use 40 psi at 70F, you'd use 37psi at 40F, and 43psi at 100F.
Click to expand...

Problem is - that forumula is based on the much larger volume of a car tire. A bike tire has a smaller volume and the same temperature change will result in a larger pressure change.
 
deilenberger said:
Problem is - that forumula is based on the much larger volume of a car tire. A bike tire has a smaller volume and the same temperature change will result in a larger pressure change.
Click to expand...

Better go back and check the gas laws, yes the volume is less, so you have fewer moles to start with, thus they offset one another in the combined gas laws.
 
pffog is right. It is not volume dependent.

PV=nRT

P=pressure
V=volume
n=number of moles of gas (quantity)
R=ideal gas constant
T=Temperature

Since for the same tire, the Volume, n, and R don't change, you get:

P=T (well, pressure is directly proportional to temp., but I can't make that symbol).

So all the other variables drop out. P is proportional to T regardless of volume, quantity of gas, etc.

If you double the temperature, the pressure doubles, etc. (But that's Kelvin I believe, not F or C)
 
RoboRider said:
pffog is right. It is not volume dependent.

PV=nRT

P=pressure
V=volume
n=number of moles of gas (quantity)
R=ideal gas constant
T=Temperature

Since for the same tire, the Volume, n, and R don't change, you get:

P=T (well, pressure is directly proportional to temp., but I can't make that symbol).

So all the other variables drop out. P is proportional to T regardless of volume, quantity of gas, etc.

If you double the temperature, the pressure doubles, etc. (But that's Kelvin I believe, not F or C)
Click to expand...

Um, not quite doubling, especially in K. n makes a lot of difference here. V can change somewhat, but not enough to really care about.

Overall, though, you're on the right track.

BTW, anyone reading the OCD thread? if not, here's the same reply:

shut up, throw a leg over, leave the extra gloves in the garage and ride the thing!:clap
 
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