tire pressure?

Do any of you guys let any tire pressure out when you go out for a night of racing?

not for around town racing, only when i go to the track.

i actually dont even let tire pressure out when at the track. For some reason my car sticks very well at the line.

well i was thinking about it as more of a safety thing. cause when going at higher speeds the air molecules inside the tire start to move more violently causing added pressure on the weaker spots of the tire. thus changing the shape of the tire and raising the pressure inside of the tire. am i wrong?

Ideal hot tire pressure for best handling is generally somwhere from 36-44 PSI depending on the tire. In a drag race or street race, lowering the pressures on the drive wheels will help the initial launch because of the softer sidewall spring rate and increased contact patch. Unless you're running your tire pressures rediculously high to begin with, tire pressure bildup is not really a safety issue.

wont 36-44psi at high speeds cause a smaller contact patch causing less control?

well i was thinking about it as more of a safety thing. cause when going at higher speeds the air molecules inside the tire start to move more violently causing added pressure on the weaker spots of the tire. thus changing the shape of the tire and raising the pressure inside of the tire. am i wrong?


:grinno: The tire pressure increases because of the heat generated by friction between the road and the tire - not because the air molecules in the tire are moving violently!

...unless your thinking about top fuel funny cars. Those tires change shape when they launch because of centrifugal force.

But hotter air molecules will move much faster and although they may not exactly be violent, this will increase tire pressure.

I'm not an expert on the subject, but I'm not sure if the air inside a tire even moves that much when the tire is spinning - kind of like how the air inside a jumbo jet doesn't move even though the plane itself is flying 600mph. It's not like there's fan blades inside the tire to disrupt the atmosphere.

Boring :sleep: L8...

Boring :sleep: L8...
Not like you've ever posted anything useful or interesting :grinno:

when molecules get hotter they expand. like an apple pie...when its cold you really dont smell it but when it gets heated the molecules expand and become more active, giving off the smell. I think thats what i was taght. :confused: all well not like it really matters anyways

Not like you've ever posted anything useful or interesting :grinno:

Not like i have to in a Street Racing Forum :icon16: . L8

wow..Math and physics...Im out

Yeah, both classes I failed miserably in. I fell asleep 85% of the time I was in them, but yet I graduated.

Schools, you wonder why half the people in this world are idiots. They just push you in and out like it's not going to affect the world. L8...

I have to retake college algebra, I failed it misreably...I did bad ass in physics in high school though...wierd. Im a poli sci major, so I like talking about real things, lol.

Yes the tire preasure in the tire does increase but only 2 lbs or so, in long ass cross-country rides where you drive like 8 hours straight then it might even go up 4 lbs but not to the point it will burts your tire.
the reaso to increase tire preasure when you go to an autocross or something is to increase the strength of the sidewall for better cornering, the contact patch may decrease by a few decimal points but the overall strength of the tire at high preasure will reduce flex and allow for better corner control.

Im a poli sci major, so I like talking about real things, lol.
I'm with you, I'm a Psychology major with emphasis towards marriage and family relations...leave that math and science crap to the people with no lives. :icon16:

thank you. thats more of what i was looking for. i asked my teacher on the topic and he explained it the best he could but he doesnt know shit about cars so he was educating himself on the topic too. i think

you know what, I have a question similiar to this too...does tire pressure change with the outside temp. too? I bring this up because this winter I had to refill my tires 3 TIMES because the air pressure kept dropping, and in the summer and warmer months, I don't have to do it at all.

i wouldnt know about that...gotta love fl! but im sure it does just not very significantly

Yeah, if the air temperature inside your tires changes, whether it's due to friction or outside weather, the pressure will change. The colder it is, the lower the pressure will be.

This isn't really advanced physics, more like common sense (all math is just common sense). Hot air expands, cold air contracts.

36-44psi isn't exactly low...

ok children settle down.

lets go back to Chemistry


Combined Gas Law- P1V1/T1=P2V2/T2

P=Pressure (in atm. mmHg or kpa)
V=Volume (in litres)
T= Tempature (in kelvin)

Pending that tires volume is generaly a constant we will only deal with p1/t1=p2/t2

Lets sya when the car tire is cool it is 20C@3atm (3atm=44.1psi)
20+273=293K@3atm

after riding around at high speeds the tempature in the tires raises 15C. 293+15=308K now lets plug it all in

3atm/293=x/308
293x=924

x=3.15atm

a rise of 0.15atm

0.15atm=114mmHg
0.15atm=2.20PSI
0.15atm=15.15kpa

not a major pressure rise.

Pop quiz:

1. Who doesn't undertand any of this? Show by a raise of hands :wave:

L8...

DoooD!!!111!!!! U Jus G0t skoold buh a H! Skoolah'. CHS Ownz Jooo!!!!111!!!

Edit:
Oh and uhhh :bananasmi :boink: :wave: :slap:

Now all Bow down before me and my supreme High School Chemitry Knowledge

:worshippy :worshippy :worshippy :worshippy :worshippy :worshippy :worshippy

I've been outta high school for 2 years now. Neener neener neeeeneerrr! While your sitting in class doing school work listening to some lame teacher, I work all day. HA! Enjoy high school, cause when you get out, not a thing you learned does diddly for you :icon16: . L8...

well not only do i go o HS i play soccer, run cross country, and work. oh and i plan on going to colledge for at least 6 years after HS....

Chemitry Eh, never studied that. Teach me more Fry. CB the Fry Guy. Has a nice sound to it. CB! CB! CB! L8...

I don't know much about chemistry..but I can teach you some spelling. CHEMISTRY, not CHEMITRY. :p







j/p :)

6 Years huh? You must be one of those kids that sits at home all day studying, then you play on the computer for a bit, then go to bed.

You need to get out and make some friends :iceslolan . L8...

"Braker one one, come back."

Lol

Well as people begin to argue over things they have no idea about i tend to like to step in an show what knowledge i do have and correct them all, muahahahaha.... so start more discussions about things chemistry related and let some false information be slurred all over the thread. think you dont understand me? jump in to the Engineering/Technical form and talk to some of thoes guys with tripple chemistry and physics degrees and see if you understand. i sure dont alot of hte time.

dampachi you are just mad because you got owned by a 10th grader. lol. boohya! oh and im sitting at work now. doing nothing. and i have friends, im just grounded from making contact with them 99% of the time.

Since when did I get owned? The only thing I said in this thread was pointing out civracers spelling mistake. Oh..and something about 36-44psi not being low tire pressure. :shrug:

Hey CB, I found that picture of you sitting on the corner of your work place:

http://files.automotiveforums.com/gallery/watermark.php?file=/503/232382loser.jpg

:lol: L8...

wanna play that game eh? look i found a pic of your car....

http://img.photobucket.com/albums/v201/CBFryman/gotdforce.bmp

lol its all in good fun, but im finished...for now

All that time looking for a Ricer pic and you couldn't even find a descent one. It's ok, you tried, and that's what counts :loser: . J/P. L8...

I don't know man..that's a pretty good one.

It's not even a Civ. Would have been much better had it been a Civic. L8...

well not only do i go o HS i play soccer, run cross country, and work. oh and i plan on going to colledge for at least 6 years after HS....

"Colledge"? Will 6 years be enough? I can't believe you people let that one go by. :grinno:

hahah. good call!

you guys argue too much

-Early

"Colledge"? Will 6 years be enough? I can't believe you people let that one go by. :grinno:

and how many times must i say english isnt my strong point. $5 and a burrito says you didnt understand my equasion...

-Midday

We don't argue much. Actually we all get along pretty good. Minus certain times...

equasion? hehe k finished

it was so-and-so's law of gasses, but it's been 4 years since I took high school chemisty, so it might as well have been written in swahili....I bet I could whoop your ass when it comes to Erikson's theory of child development stages though.

I'll take that burrito bet. I could really go for one right now...

all this cause i asked a ? about tire pressure...ha

That's how these threads are. haha.

its all good fun though. but its amazing...if you read, almost every thread turns into some sort of arguement

if we didnt argue then that would mean everyone would have the same opinion and intelegence level. this means that all questions could be answeared with one thread. actualy that means there would be no questions. that is scary...
But 'tis a liberal's paradise, all things being 100% equal....

Oh, and the law i used was a modified version of the combined gas law, and i dont car about the stages of child development, as far as im concerned i could be castrised, makes all sex safe, but it kills your testosterone supply, and i love my testosterone.

A little too much info there CB. L8...

Guys, guys, guys... Don't fight, its not civracers fault he dosent care about the laws that back up common sense. And some of this stuff IS actually usefull, It proved very usefull in college Chemistry since I only went to 5 of the lectures (mostly for tests) and got a B+. So keep doing what you like and don't think less of people for having different interests or tallents.

And for the record I don't think you should let out any pressure for fear of bursting if your in the recomended range. Maybe if you have some traction issues but not more than a few pounds so its not so bouncy.

PPS: What are you going to study CFB? And is that extra two years for a masters?

Im not sure exactly, im thinking Graphic NEgineer or somehting involving Physics. i may take a few chemistry classes just because. and yes the 2 extra years is to btain my masters. eventually i would like to get my PHD but after my masters i will just take night classes on and off untill i obtain my PHD.

I don't care about it because that's not the route I'm taking. It's cool that CB is going that route. He seems to be the type that would accomplish great things. I'm just giving him crap, because it's all in good fun. I'm surprised I even graduated, but here in Springville, it doesn't take much to graduate :rolleyes: . L8...

well...there is fighting and there is having intelligent conversation. most of this is fighting, like the name calling and stuff. but it started with intelligent conversation.

DO NOT drop the tire pressure in your street tires. nothing good will come of it. they are designed perfectly to run at the optimum pressure levels. dropping the tire pressure will only give you less traction. and create uneven wear.

drag radial and slicks have soft sidewalls and sticky rubber, they will benefit from lower pressure. your street tires dont have either.

at speed for long periods of time on certain tires, mostly y rated and up you will see a warning to drop tire pressure by 2-4 pounds because of heat expansion. (the air inside heats up and expands) you drop the pressure to compensate for the expansion so that the outer tire diameter and shape stays the same.

the exact opposite happens in the cold winters up north, you will have a low tire pressure condition when you wake up in the mouring. dont fill up the tires, when the air gets back to tempeture they could explode. ford had problems with this in there SUV tire pressure gauges. it would read low pressure in the winter people would fill them up and they would explode down the street. if they have been driven on for a while and still look low check them and only fill them if need be.

as for the pro drag cars, the tires expand because of the extreme forces against them, and they are designed to do that, for what reasons im not sure

DO NOT drop the tire pressure in your street tires. nothing good will come of it. they are designed perfectly to run at the optimum pressure levels. dropping the tire pressure will only give you less traction. and create uneven wear.

I wouldn't reccommend dropping tire pressures below about 25 PSI (cold), but most tires are safe that low. It WILL help the initial launch, though cornering may be compromised.

drag radial and slicks have soft sidewalls and sticky rubber, they will benefit from lower pressure. your street tires dont have either.

Most street tires have very soft sidewalls. For straight line acceleeration, total grip of a tire is a function of the surface area of contact. Lower tire pressure = larger contact area = more grip = better launch.

at speed for long periods of time on certain tires, mostly y rated and up you will see a warning to drop tire pressure by 2-4 pounds because of heat expansion. (the air inside heats up and expands) you drop the pressure to compensate for the expansion so that the outer tire diameter and shape stays the same.

This is correct in some tires, but in most cases the required speed is around 130 before you even have to consider it.

the exact opposite happens in the cold winters up north, you will have a low tire pressure condition when you wake up in the mouring. dont fill up the tires, when the air gets back to tempeture they could explode. ford had problems with this in there SUV tire pressure gauges. it would read low pressure in the winter people would fill them up and they would explode down the street. if they have been driven on for a while and still look low check them and only fill them if need be.

This depends on how cold it is and how cold it's going to get. If it's going to be < 30F for a while when you're driving, adding a couple of PSI is usually a good idea as long as you bleed it out once it gets warm.

[as for the pro drag cars, the tires expand because of the extreme forces against them, and they are designed to do that, for what reasons im not sure

The rear tires in the top fuel cars get taller and narrower at high speeds primarily due to centripital force. This allows a bigger contact patch at the launch when the grip is needed the most, and a smaller contact patch at higher speds where you're not going to spin the tires with 7000 HP. The Top Fuel cars are also single speed, and the larger tire diameter gives results in gearing that gets taller throughout the course of the run, eliminating the need to shift.

Cold tire pressures of various race cars:
Top Fuel Dragster rear: 4-6 PSI
Nascar Nextel Cup: 25-50 PSI depending on track and which corner of the car the tire is on
Formula 1: 16-20 PSI
CART: 14-18 PSI
Light Formula cars: 12-18 PSI
Sports Car (slicks): this varies a lot depending on the tires used, but generally 18-24 PSI
Sports Car DOT Track Tire: 25-35 PSI

Again, keep in mind that these tire pressures can vary a lot depending on a number of different factors, but for pretty much any street tire, 25-28 PSI (cold) on the drive wheels and 35-40 PSI (cold) on non-drive wheels will give the best straight line acceleration.