Tire growth is HUGE on a TF/FC. That actually gives them a variable gear ratio. I believe there is a fixed (3.20) ring and pinion ratio they must run. My guess is that the new tire might have a little growth limiting, but I think the min. pressure is for retention in the rim. Tire construction determines growth, not pressure. These are most certaily not steel belted tires.

Heat from flexing of the tire cords and rubber is what fails tires, and TF tires go thru some horrendous contortions as well as 320+ mph, but the good news is they only turn about 200 total revolutions under power and maybe the same for shutoff but just coasting.

I can't see tire pressure changes having much to do with starting line traction. Min TF pressure is now 7.0 psi. Jeeze, I wonder what thery were running before the new rule?

My $.02

 

Actually, pressure has a big impact on starting line traction. Too much pressure, and the car would seem to get up on the tire too quick and cause tire shake, and too little pressure would cause it to be lazy off the line. This new tire is probably much different in terms of how it reacts to pressure, so with the new limits, teams will have to tune the engine and clutch differenty to compensate.

We ran tire pressures in the 5.5-7.5 range on the 'old' tire (beginning of this season), depending on conditions. This was on a Funny Car.

 

Thanks. Of course you are correct. 0.5 psi is a big % of change change on a 6.0 psi inflation. How sensitive is the tire to pressure? Do you adjust in 0.1 psi increments or more like 0.5 psi? I think FC min is 6.5 psi for the new tires.

Are both rear tires the same inflation pressure?

How many runs does a tire last? Does shake harm the tire (eg: irregular wear, cupping or the like?)

Do you balance the wheel/tire assembly? Seems like a dumb question, but with the gyrations the tire goes thru and the standing distortion wave behind the contact patch, my thought is that tire uniformity, or consistent construction and thickness around the tire, would be more critical than static balance. I think a driver might feel a "bad" tire the first time he ran it, or maybe even during a burnout.

 

Please tell me tire pressure has some impact on tire expansion?

If I think of air like the fluid that it is, wont the tire have more difficulty "displacing"
the air within the tire to shape itself?

For lack of a better comparison, if we were to fill the tire with water completely,
wouldn't the structure of the tire itself become more rigid and not allow as much
expansion?

Or, will the water just move to where the force is taking the tire since volume
is pretty much equal no matter how the tire shapes itself?

P.S. By "shape" I mean, expanding like it will does during a burnout as opposed
to stretching to achieve the effective gearing (Centrifugal > tire OD).

When you guys are referring to expansion, are you inferring that the compound
will stretch to a greater volume as well?

I bet with the downforce of the spoiler at mid track, these tires don't
balloon up like they do during a burnout

 

air's not a fluid, it's a gas. As such, heating the air has a substancially larger pressure or volume increase than any fluid would show.

Your concern about "displacing air" is actually more of "compressing air".

While the MASS of air inside the tire stays relatively constent (although most slicks leak a bit) the pressure and volume are dependant on temperture of the air and shape the tire takes on (ie. pressure drops if the tire hops in the air and the carcass expands... and increases when the tire wrinkles and the volume decreases).

 

Thanks for the reply Steve. With every clarification, there comes confusion.

Not to get off topic, but...

I've heard and read so many times when people talk about Fluid Dynamics,
they refer to air as a fluid. What are they talking about?

 

as a nerd who's taken some fluid dynamics and chemistry classes..... allow me to let somebody else explain it

fluid
noun

1. A substance, such as a liquid or gas, which can move about with freedom and has no fixed shape.

Thesaurus: liquid, vapour, solution.
adj

Thesaurus: adaptable, changeable, flexible, mutable, unstable.

 

To add to Jimmy's definitiion:

"By definition, a fluid is a material continuum that is unable to withstand a static shear stress. Unlike an elastic solid which responds to a shear stress with a recoverable deformation, a fluid responds with an irrecoverable flow.

"[noun] a continuous amorphous substance that tends to flow and to conform to the outline of its container: a liquid or a gas."

Although the first definition is probably more exact, the second is more intuitive and more obvious to me.

Of course some materials may exist as solids, liquids or gasses depending on temperature and pressure conditions. Water is a good example.

 

Good stuff everyone. It's so difficult to think, "out of the box" when you were
raised "in the box".

I wish I had the engineering and physics background many of you have.

I think, "Peanut", you all think, "BaCl2(aq) + Na2 SO4(aq) ----> 2NaCl(aq) + BaSO4(s) "

 

Formation of precipitate (fun stuff)

You're right, this has been a very informative post, although I haven't added anything to it, just wanted to say thanks for the knowledge everyone.

 

ditto, i love reading this forum, lots of intelligent guys here

i'd post more, but being a poor college student i've barely been able to put a wrench to my stock ls1 i can dream though

 

Here are the pictures of the heads and TF team car I promised!

Check out the design of these heads. The tech was throwing these around
like rag dolls.

http://members.rogers.com/tdese739/promodheads.jpg

Other stuff
http://members.rogers.com/tdese739/topfuelvalve.jpg
http://members.rogers.com/tdese739/topfuelrods.jpg
http://members.rogers.com/tdese739/topfuelmagneto.jpg

This is the team that let me take video and pics (nice people!):
http://members.rogers.com/tdese739/topteam.jpg

 

you didn't get a picture of the chambers or the ports, did you?

 

Wow, thats a lot of reading. Did anyone mention that there are supposedly two lifters on the exhaust valve? I don't know if this is correct, but I have read where they place two lifters on top of each other on the exhaust valve. I guess to dissipate some load or something. Oh, and by the way, anyone who hasn't experienced a top fuel run has to go as soon as possible. I was in the pits when the Miller car was idling. Dick Laheye just barely cracked the throttle and unleashed this tremendous roar. Oh and by the way, standing 15 feet behind a nitro car isn't a good idea unless you want to start crying from the smell of nitro.

 

At first it almost smells good, but then it really starts to get you!