I’d thought about this too… no WAY can I see it working in “real world” conditions though.
I’m happy to have TPMS on my car though, problem is you have to re-initialize it when you change wheel sets, and AFAIK that can only be done on the dealer’s Consult II computer not at home, so I would only get it on slicks, or only rains, or whatever. I just bought a really nice gauge and check before I go out for a session and when I come back in - at this point I’ve got my cold temps down quite perfectly so that I gain exactly what I want after the first lap and a half.
The first post was a very nice description of a pressure relief valve. A spring holding a valve shut, with an adjustment screw setting the “x” part of your F=kx equation, where F is proportional to the amout of pressure required to move the spring and thus open the valve. There’s a million of them all over the oxygen plant that I’m wasting half my October at, but that’s neither here nor there.
But yeah as Newman pointed out before this got out of hand, in addition to thermal expansion, tires see lots of pressure spikes that would get relieved through the valve and you would wind up with 4 flat tires.
The first post was a very nice description of a pressure relief valve. A spring holding a valve shut, with an adjustment screw setting the “x” part of your F=kx equation, where F is proportional to the amout of pressure required to move the spring and thus open the valve. There’s a million of them all over the oxygen plant that I’m wasting half my October at, but that’s neither here nor there.
But yeah as Newman pointed out before this got out of hand, in addition to thermal expansion, tires see lots of pressure spikes that would get relieved through the valve and you would wind up with 4 flat tires.
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right just a simple example would be under hard braking, the weight of the front end of the car would be “heavier”… exerting more force on the front tires, increasing the pressure in them (assuming the volume of the tire doesnt increase), pretty much common sense, im not an engineer cough fry, so excuse my horrible physics terms, lol, but i learned that stuff on my way to doctor school…
edit: but no seriously can an engineer or someone more inclined than i, explain if my logic is off? im just spitballing, also the valving wouldnt work because on the straights as you pick up speed the downforce on your car increases if you have a wing/undertray or such, which would result in purging of the tires, then when you slow down to a hairpin or something you have flat tires, lol
:forehead slap: I’m ashamed for forgetting this part: Most of the thermal expansion of “air” is due to the water vapor in the air. If you want to avoid most of it, fill your tires with nitrogen. Whether the nitrogen is made with PSA, membrane, or cryogenic separation, all of them produce an extremely dry product. No water vapor = significantly reduced thermal expansion.
speedracer your logic is spot on as far as I can tell, but I’m an engineer. Common sense tends to elude me.
It’s not a “problem” you shoot for a hot temperature based on air pressure and go with it. For the track you’re at you can always find the sweet spot to balance temperature and pressure and not blister the tire. It’s easily doable if you keep track of temps and psi religiously with a good notebook.
Stupid dry air and using things like CO2 in the tires. They still get fluctuation.
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luckily though there are standard curves (not linear of course, duh) which they can calculate exactly how much the pressure increases, due to the expansion of gas as temp increases…
I would say it would work if it could blead into say a hollow rim and have a valve that would allow the air to go back and forth at a desired psi.Kind of like when you squeeze and empty plastic bottle and it sucks the air back in when you let go.I am not saying it is possiable but it would be cool.
luckily though there are standard curves (not linear of course, duh) which they can calculate exactly how much the pressure increases, due to the expansion of gas as temp increases…
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Right. Same thing applies to the amateur at a racing event so he can set his cold tire pressure properly and not need fancy valves
ding ding ding… nitrogen. Doesn’t expand much at all at tire temperatures. Set it and forget it. It will still leak over time, so it has to be topped up. If topping it off with regular air, the tire should be perged and re-inflated with nitrogen afterwards. There are local places (Dunn Tire) that do nitrogen fills.
CART and F1 and maybe indy cars use a bleeder valve system that bleeds off the extra air pressure. I’m sure you can buy them but I would imagine they are pretty pricey. This helps on the start of the runs since they can keep the air pressures set to what they want for the whole run unless a yellow comes out.
ding ding ding… nitrogen. Doesn’t expand much at all at tire temperatures. Set it and forget it. It will still leak over time, so it has to be topped up. If topping it off with regular air, the tire should be perged and re-inflated with nitrogen afterwards. There are local places (Dunn Tire) that do nitrogen fills.
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Yea the local places that do fills usually charge an arm for what you get and its never pure enough nitrogen. There is always moisture in there so IMHO its not worth it for your average weekend racer. But a weekend racer with too much $, should be fine
Yea the local places that do fills usually charge an arm for what you get and its never pure enough nitrogen. There is always moisture in there so IMHO its not worth it for your average weekend racer. But a weekend racer with too much $, should be fine
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they make attachment that goes onto your air compressor that gets the water out of the air that works very well.
the coefficient of nitrogen is only .2 better at best (since you’re probably not getting a pure fill) so it’s not really worth it unless almost free. equate that to an expansion of maybe 3-4psi at at track day instead of 4-6psi (my experience with street tires).
just not worth it.
I pretty much expected the result of this thread would be that it wasn’t worth it, but it’s a good topic, idea to talk about.
the coefficient of nitrogen is only .2 better at best (since you’re probably not getting a pure fill) so it’s not really worth it unless almost free. equate that to an expansion of maybe 3-4psi at at track day instead of 4-6psi (my experience with street tires).
just not worth it.
I pretty much expected the result of this thread would be that it wasn’t worth it, but it’s a good topic, idea to talk about.
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well said, i forgot who it was a few months ago but they were talking about filling their tires up with helium… i lol’d
pretty much common sense, im not an engineer cough fry, so excuse my horrible physics terms, lol, but i learned that stuff on my way to doctor school…
