time to change air

[RandyO]

it's getting that time of year to take the summer air out of your tires and put the winter air in

[Josephd14]

I Did this last year, what a Difference it madr.. Sounded corny but worked out great..

[OreoGaborio]

i still have winter air in... can i run it as is or should i change it out for fresh? how many miles do you go between air changes? I didn't do that many miles on my bikes this year.

[Cheese]

Can I just bleed it or do I need a flush kit?

[Loun]

Luckily I hit it just right, put new tires on the bike a month or two ago so I have a great mix of the two seasons in there. I think it provides the best traction IMHO

[ALL BLACK 06]

Time to upgrade to nitrogen......and get those cool green avlve covers.

[The Snowman]

Oh damn, I never changed my air this season. No wonder it feels funny.

[wookie]

I'm not changing untill I have to -- I don't want to lose the 5-6 hp.

[ChikkenNoodul]

It's best to put colder winter air in than you need, so I send my wheels to Saskatoon to get the good stuff.

[butcher bergs]

I run 4 season air....it's a bit generic and I'm not making the MPG I could be with season-specific air, but I never have down time and I get alot of grip in the snow.

[RandyO]

apparently everyone thinks this thread is a joke, it's meant as a reminder that air pressure flucuates significantly during the change of seasons

I discovered day before yesterday my rear tire was down to 28 from 41, last time I checked was a week ago, and it's been consistently at 41 all summer...

[978chris]

I run 4 season air....it's a bit generic and I'm not making the MPG I could be with season-specific air, but I never have down time and I get alot of grip in the snow.

hahaha

apparently everyone thinks this thread is a joke, it's meant as a reminder that air pressure flucuates significantly during the change of seasons

I discovered day before yesterday my rear tire was down to 28 from 41, last time I checked was a week ago, and it's been consistently at 41 all summer...

checking tires cold?

you still have the same mass of air in the tires, it's just that in the colder mornings now the cold pressure difference vs. operating temp is going to be greater, since the molecules are all crawling up inside like your peepee in the ocean.

check them hot. if you fill em too much while they're cold then they'll be over once you're riding.

you probably already know all this; if so just ignore me. been stuck at home a week on massive oxycodone pills and feeling pretty stupid. i've just never seen an actual fluctuation (once warmed up) that is as big as what you mentioned that didn't involve some other issue (leak etc). but this is my first season riding in a cold part of the country, so....

[KB]

Ohhhhh no he didn't. Here we go for the 40millionth time on the cold vs warm tire pressure thing.

KB

[richw]

Randy checking tires a good thing...

That much change and I vote for slow leak

what did the other tire do ?

[Billy]

I run helium in my tires. Makes the bike soo much lighter!!!! Oh don't forget blinker fluid flush!

[Honclfibr]

A good rule of thumb is about 1psi change in cold tire pressure for every 10 degree farennheit change in ambient temperature. It will vary depending on the volume of the tire, but that's a good average.

[Mad Max]

To analyze this a little more scientifically, lets use the ideal gas law

PV=mRT

Pressure*Volume=mass*gas constant*temperture

Units matter of course, lets stick with english since everyone knows them. We have to use an absolute temperature scale which is has zero at absolute zero and in the English system that's the rankine scale. One rankine degree has the same change as one farenheight degree. Pressure is in psia, Pounds/inches^2 in the absolute scale. Absolute measures pressure relative to a vacuum as opposed to gage pressure that you get on an ordinary pressure checker which measures relative to atmospheric pressure (~14.7psi)

We can re-arage the original equation which yields

P/T=mR/V

This is helpful since mass, the gas constant, and the volume of the tire can be considered to be constant from one temperature change to another. This allows to equate one temperature and pressure situation to another.

P1/T1=P2/T2

P1 and T1 are the Pressure and Temperature in case one and P2 and T2 are the Pressure and Temperature in case 2


So for instance, let's say that we inflate our tires on a 90 degree Fahrenheit day to the recommended temp of 35psig. Then the temperature drops to 40 degrees Fahrenheit, what will the pressure be?

35pisg = 49.7psia = P1
90 F = 550 R = T1

40 F = 500 R = T2

thus
49.7psia/550R = P2/500R

P2=30.5 psig

At 20 Fahrenheit
Pressure drops to 28.6 psig

At 0 Fahrenheit
pressure drops to 26.8psig


Now for a different case, let's say that you inflate your tires on a cold morning before a trackday it's nipply out (30 Fahrenheit) and you go with 28psig knowing that they will warm up a bit. What will the pressure be when you are riding at full tilt and the air in the tires is 140 Fahrenheit?

28psig = 42.7psia
30 F =490 R

140 F = 600 R

42.7psia/490R = P2/600R

P2= 37.5psig


Try it out yourself.

Honclfibr, your rule of thumb is a pretty good average. However, it is incorrect that the volume of the tire matters, it is irrelevant.

[OreoGaborio]

Check your tire pressure regularly & adjust accordingly

Well put, Chris!

[hammadown]

Is someone studying for a general chemistry exam? You get an A nice work!

To analyze this a little more scientifically, lets use the ideal gas law

PV=mRT

Pressure*Volume=mass*gas constant*temperture

Units matter of course, lets stick with english since everyone knows them. We have to use an absolute temperature scale which is has zero at absolute zero and in the English system that's the rankine scale. One rankine degree has the same change as one farenheight degree. Pressure is in psia, Pounds/inches^2 in the absolute scale. Absolute measures pressure relative to a vacuum as opposed to gage pressure that you get on an ordinary pressure checker which measures relative to atmospheric pressure (~14.7psi)

We can re-arage the original equation which yields

P/T=mR/V

This is helpful since mass, the gas constant, and the volume of the tire can be considered to be constant from one temperature change to another. This allows to equate one temperature and pressure situation to another.

P1/T1=P2/T2

P1 and T1 are the Pressure and Temperature in case one and P2 and T2 are the Pressure and Temperature in case 2


So for instance, let's say that we inflate our tires on a 90 degree Fahrenheit day to the recommended temp of 35psig. Then the temperature drops to 40 degrees Fahrenheit, what will the pressure be?

35pisg = 49.7psia = P1
90 F = 550 R = T1

40 F = 500 R = T2

thus
49.7psia/550R = P2/500R

P2=30.5 psig

At 20 Fahrenheit
Pressure drops to 28.6 psig

At 0 Fahrenheit
pressure drops to 26.8psig


Now for a different case, let's say that you inflate your tires on a cold morning before a trackday it's nipply out (30 Fahrenheit) and you go with 28psig knowing that they will warm up a bit. What will the pressure be when you are riding at full tilt and the air in the tires is 140 Fahrenheit?

28psig = 42.7psia
30 F =490 R

140 F = 600 R

42.7psia/490R = P2/600R

P2= 37.5psig


Try it out yourself.

Honclfibr, your rule of thumb is a pretty good average. However, it is incorrect that the volume of the tire matters, it is irrelevant.

[RandyO]

Randy checking tires a good thing...

That much change and I vote for slow leak

what did the other tire do ?

probably, but I haven't found one, the past few days I've been checking a couple times a day with no loss

probably a nail that leaked at first but has sealed itself, sprayed the tire with soapy water, nothing that's obvious

ny normal routine every morning I pinch the tires in my hand for the obvious, and once a week, I use a tire gage,

front tire was down 3psi

[richw]

Schraeder valve it can be seated or have a tiny dirt and not quite seal
or it may need to be snugged

Its another Liberal Conspiracy

[Mad Max]

Is someone studying for a general chemistry exam? You get an A nice work!

No, just recalling some of the basics from a Thermodynamics course. And I got a C

[richw]

I have to do it

Boyle's law is

pv = nrt

but otherwise pretty dawm close

[Mad Max]

You're right, that is the classical form of the ideal gas law. However n is simply the number the mols of the substance which like mass remains constant and has no bearing on the ratio P/T also being a constant.

[wookie]

No, just recalling some of the basics from a Thermodynamics course. And I got a C

haha, Thermo is a bitch. I got a C also.