tire pressure measurement

[ChromeWhore]

I have the new set of tires. my buddy says keep the proper air pressure in them and check the tire pressure when the bike is cold. WTF, what's cold? He never answered. I take it he doesn't know either..

Should I set the bike outside in the freezing cold? Is cold 32 degrees, 40 degrees, hell 80 degrees? It doesn't get super cold in So Cal.

What is cold tire pressure?

[truck]

Cold is whatever the ambient temperature is AND the bike hasn't been ridden in the previous 3 hours.

[FLTRI]

Cold is whatever the ambient temperature is AND the bike hasn't been ridden in the previous 3 hours.

I have found using whatever the sidewall says for max cold for the pressure I start my ride with is safe and works well.
Different tire mfg make tires differently, especially sidewall stiffness, consequently the required pressures change to maintain good handling characteristics.
HTH,
Bob

[Princess Butt]

Check them in the morning before heading out.

I keep an old fashioned bicycle tire pump handy. Gets me some exercise and pumps up the tires.

If you're running stock Dunlops, add 2 pounds to the factory recommendations. The tires last a lot longer and the bike does handle much better.

[hombre912]

Tire pressure will increase about 1 psi for every 13 degree rise in temperature.  If you set the pressure on a cool morning and are expecting temps to rise considerable during the day, this is important to keep in mind.  I never inflate tires past the recommended pressure.

[calgary56]

Here's an excerpt from an article I wrote for a column in the Canadian Armed Forces Paper, when I was a Canada Safety Council Motorcycle Instructor, while stationed at CFB Baden Soellingen in Germany back in the late '80's. It was hard enough for me to hunt this down, let alone the Motorcycle Magazine(s) where I researched the info. Keep in mind, I used to ride a Ducati 900 S2 back then, not a Wide Glide, but the principle is sound.

"Those that demand the most from their tires set the pressure for their load and speed so that the HOT tire pressure is 4 to 6 psi greater than that of when the tire is cold. If it goes up more (due to the heat caused by hard riding), add more pressure, conversely, if it doesn't increase that much, or not at all, reduce the tire pressure slightly."

[FLTRI]

"Those that demand the most from their tires set the pressure for their load and speed so that the HOT tire pressure is 4 to 6 psi greater than that of when the tire is cold. If it goes up more (due to the heat caused by hard riding), add more pressure, conversely, if it doesn't increase that much, or not at all, reduce the tire pressure slightly."

A bit of explanation about recommended pressures:
Tire sidewall construction acts like a spring that helps air hold the bike up. Different sidewall construction can be from one tire model to another (ie: dunlop 401 vs 402 vs E3), or from mfg to mfg (ie: Dunlop 40lbs vs Metzler 50lbs) due to each's idea of the ultimate sidewall construction.

IMO, it's best to go by whatever the tire mfg (on sidewall) recommends.

Bob

[ChromeWhore]

This is interesting stuff. There has to be an ambient temperature to constitute cold tire pressure. If I rode 10 miles in 20 degree temp in Minnesota, would tire temp be the same as a tire sitting half the day in 100 degree temp in Phoenix? Logically thinking, I'd say both environments are different. So a tire riding in 20 degree temp all day would still be considered cold relative to the tire sitting in direct sunlight in Phoenix.

[IndyHarley]

checking your tire pressure when 'cold' simply means checking the pressure before you ride the bike or it has not been ridden for several hours. Conversely when you ride the bike and check the tire pressure you are checking the tire pressure when hot because you have ridden the bike.

[boooby1744]

Tire pressure will increase about 1 psi for every 13 degree rise in temperature.  If you set the pressure on a cool morning and are expecting temps to rise considerable during the day, this is important to keep in mind.  I never inflate tires past the recommended pressure.

actually i believe that is 1 psi for every 10 degrees,unless you have nitrogen, which expands less and requires a higher cold tire pressure.

[Norton Commando]

According to Charles' law, tire pressure will increase from 32 psi to 34 psi when the temperature increases from 50 degrees F to 80 degrees F.

Converting from degrees F to degrees Rankine you have 50F=510R and 80F=540R

Solivng for X psi in the equation: 510R/32psi = 540R/X psi, you get 34 psi, or 2 a psi increase over a 30 degree increase in temperature.

[FLTRI]

According to Charles' law, tire pressure will increase from 32 psi to 34 psi when the temperature increases from 50 degrees F to 80 degrees F.

Converting from degrees F to degrees Rankine you have 50F=510R and 80F=540R

Solivng for X psi in the equation: 510R/32psi = 540R/X psi, you get 34 psi, or 2 a psi increase over a 30 degree increase in temperature.

Just 1 of many reasons to just use the recommended pressures from the tire's sidewall. Then fugetaboutit and ride knowing you have plenty air in your tires.

By far and again the plethora of dangerously low tire pressures (<25lbs) I come across daily tuning bikes, is much more disconcerting than the 1 in 1000 that come in overinflated. 
Bob

[boooby1744]

I thought the info on the sidewall is recommended MAXIMUM tire pressure.................

[mayor]

I thought the info on the sidewall is recommended MAXIMUM tire pressure.................

most state clearly that it's a "cold" rating.

[ChromeWhore]

Again, what is cold tire temp? You don't want to check pressure once you rolled on the tire because it heated up. Why not call the tire cold in 20 degrees after riding? It's still a cold tire to the guy in Phoenix.

There has to be a standard for what is cold. If not, everybody has different tire pressure at the same 40psi reading...

Not tryin to be a smarty, but I haven't heard any standard... This is a tougher question than I thought..

[Tsani]

It is actually referring to the temp of the air contained in the tire.
I am sure there is a test standard used for tire design  but for the most part this would be impractical for the average person to use. It's all relative and what you are looking at or for is the effect of a change in temperature of the air contained within the tire.

*taken from DOT*

While some people think that the term “cold” tire relates to the outside temperature, it really has nothing to do with the weather. It can be 90 degrees outside and your tires can still be considered cold. Rather, a cold tire is one that hasn’t been driven on for at least 3 hours, which is the optimal time to get an accurate pressure reading. A tire that has been driven on for short distances â€" even just 1 mile â€" is no longer considered “cold.”

[FLTRI]

There has to be a standard for what is cold. If not, everybody has different tire pressure at the same 40psi reading...

I don't think that can happen. 40 psi is the same no matter where, how hot or cold it is. Kinda like the pound of lead or the pound of feathers.
Here ya go:
Most all tire mfg use between 65-75 degs F ambient for their cold pressure standard.

You have the correct pressures when your tires increase between 0 and 6 lbs over what you started at.

This means if you start with 40 lbs and ride for an hour and you pressure went up 1 lb....perfect!
If your pressure went up 5 lbs... perfect!
If your pressure went up 12 lbs you need to start with more pressure.
HTH,
Bob

[Bakon]

Don't know which thread is worse, this or the kill switch one.

[Joncin]

Even though it comes up fairly often and people get tired of it, talking about tire pressure is an important subject for safety, ride quality, and tire longevity issues.

Pressure is pressure at any temperature. Manufacturers determine tire pressure recommendations using a cold (ambient temperature) tire because it's at a constant and pressure hasn't been altered by heat. Trying to determine proper pressure on a hot tire at the gas station is impossible.

When underinflated, tires build a lot more heat, cause extreme wear and dangerously flex the sidewalls to the point of rubbing.

Running the max pressure doesn't. 

[Twolane]

Measure cold pressure? I used to dismount my tires, put 'em in the freezer, take 'em out, re-mount them and THEN measure the pressure.

Now you guys are telling me I have to use ambient temperature. Where the heck am I going to put my tires to get an ambient temp? It all sounds just too simple if you ask me - not that anybody is asking me.

I think this is a good as any time to push out my TacoFry Oil Co. products. Order two, and get a third for absolutely nothing!

[ChromeWhore]

Don't know which thread is worse, this or the kill switch one.

I think this thread is gonna go to shyt anytime now...

Measure cold pressure? I used to dismount my tires, put 'em in the freezer, take 'em out, re-mount them and THEN measure the pressure.

Now you guys are telling me I have to use ambient temperature. Where the heck am I going to put my tires to get an ambient temp? It all sounds just too simple if you ask me - not that anybody is asking me.

FLTRI:Thanks for the ambient temp. That's straight forward stuff. What I was trying to say about 40psi is that if I was to air up in So Cal, by the time I get to Minnesota, my tires might be dangerously under inflated.

This is kinda an effin-A situation, you know.. 

[Dennis The Menace]

CW, I think you got some good info here.  I was taught to check air in the tires before driving, since driving creates friction and thus heats the tire and air inside it.  Its friction that provides traction, and heat is a byproduct of that friction. 

My dad raced karts and stock cars years ago, and tire pressures were adjusted throughout the day depending on track surface and air temps, just as its done on race tracks today.  I worked the pits for a few seasons and learned this stuff.  I figure if its good for race tires its good for ours.

But, I do admit the Avons I have run had to be over inflated....but thats anotehr thread I suppose.

Dennis

[hombre912]

According to Charles' law, tire pressure will increase from 32 psi to 34 psi when the temperature increases from 50 degrees F to 80 degrees F.

Converting from degrees F to degrees Rankine you have 50F=510R and 80F=540R

Solivng for X psi in the equation: 510R/32psi = 540R/X psi, you get 34 psi, or 2 a psi increase over a 30 degree increase in temperature.

If you redo your charles-law calculations to two decimal places, you get an increase of 2.24 psi over a 30 degree increase in temperature.  This is the same as 1 psi increase for every 13.39 degree increase, which is what I said.

[dusty1]

Check the pressure before going for a ride,inflate no more than max "cold pressure" on sidewall.Tires get hot when rolling,causing the air to expand,resulting in too much air pressure.That will cause a rougher ride,not really a blowout,though possible.Leading cause of tire failure:under-inflation.Running 10 lbs low is ok,more than that,not cool.If your tire says 40 psi max ld cold,then inflate no more than that BEFORE riding,though riding to the gas station for air is still a cold tire as long as its not a 20 mile ride

[ChromeWhore]

 

I have a fetish for tire pressure... I got my a$$ kicked on the Metzler thread behind tire pressure.. effin-A! Here we are again... Maybe tire pressue is just something pricks worry about..