Reduce tires pressure by increasing wheel temperatures?

[bhall II]

It appears he's suggesting there's some sort of "shutter" effect that separates air pressure in the hollow rim from air pressure in the tire, thus lowering tire pressure at speed by virtue of reduced volume. I think.

Would that not violate the ideal gas law, though? Fixed volume is fixed volume.

[hollus]

Separating the two flows is one thing, separating their pressures another. Interesting that you bring up the gas law. It would appear to violate it, yes, but it might just not apply here, one simplification too many. The ideal gas law would not allow for Bernoulli, for example, I think, and he is suggesting internal eddies, shear gas flows, etc in the tire, so local low pressures might be possible? I have a hard time seen his movements and an even harder time seen how it would have a significant effec by the relatively clean tire surface.
Very happy to learn here, Matt, are you reading? (I am sure you are).

Yup, I also cannot see how that shutter effect would change "the volume".

[.poz]

To me, what is described in that article break some rules of physics.....

I think is far more simple, and it's al about the definition of wheel in the rules:

definitions

1.5 Wheel : Flange and rim.
1.6 Complete wheel : Wheel and inflated tyre. The complete wheel is considered part of the suspension system.

then we have

12.8.3 A complete wheel must contain a single fixed internal gas volume. No valves, bleeds or permeable membranes are permitted other than to inflate or deflate the tyre whilst the car is stationary.

A wheel rim with a sort of "double deck" and a calibrated valve to allow gas bleeding in the internal part of the rim over a certain pressure is legal because the gas is still in the "complete wheel"

Sure you can't use a simple pressure calibrated valve, you need something that alow slow bleeding but close on spikes (i.e. hitting a kerb) and possibly something to engage the system only when the car is moving (easy with centrifugal force as a trigger)

[zac510]

But the FIA, in response to McLaren's question, already clarified that a double chamber wheel rim is illegal. There is no liberal interpretation of 12.8.3 allowed because of this clarification.

reference: http://www.motorsport.com/f1/news/mclar ... ve-735663/

[hardingfv32]

How about a ultra small opening between the main tire chamber and spokes. This opening is fixed so it could be stated that there is a contiguous chamber. The spokes are setup with a vacuum and the main chamber bleeds pressure off into the spokes.

Brian

[1158]

Could this work?

Heat the air before the tyre is inflated so that the pressure is what the FIA require. Once the cars are rolling the hollow spokes cool faster (possibly with help from the brake ducting) and cool the air within them as well. If the holes between the spokes and the wheel are small (but still fixed) it could limit the cooler air from mixing with the outer hotter air. As the air trapped in the spokes cools it decreases in volume which bleeds some of the air outside the spokes into the center section. The process would continue until the air temp in the spokes stabilized.

Does that make sense while not violating any laws of physics?

[erikejw]

When Max crashed during qualy his front left leaked very moisty air from the rim. When he crashed in the race the same happened leak came through his break ducts.

My guess is that they fill their tires with very hot moisty air/nitrogen. When they cool off the pressure lowers due to lower kinetic energy from the gas molecules AND the moist/water molecules form water drops(some of them).

Water has higher density than moist so the formed droplets lowers the pressure additionally. Less gas molecules(more droplets) and less energy in them due to lower temps.

A double whammy.

The phase shift from gas to water happens at all temperatures not only close to boiling temps. More heat, more gas molecules, higher pressure in a contained space.

I think that is what RB(and maybe others) are doing. Quite ingenious.

[PlatinumZealot]

Could this work?

Heat the air before the tyre is inflated so that the pressure is what the FIA require. Once the cars are rolling the hollow spokes cool faster (possibly with help from the brake ducting) and cool the air within them as well. If the holes between the spokes and the wheel are small (but still fixed) it could limit the cooler air from mixing with the outer hotter air. As the air trapped in the spokes cools it decreases in volume which bleeds some of the air outside the spokes into the center section. The process would continue until the air temp in the spokes stabilized.

Does that make sense while not violating any laws of physics?

It makes sense but it is a double edged sword. The air in the spokes would also heat faster under braking, just before the turn, when you actually need the pressure to be low right?

[Jersey Tom]

When Max crashed during qualy his front left leaked very moisty air from the rim.

You're making this conclusion based on what, exactly?

[PlatinumZealot]

As a poster mentioned before the whole problem is not about trying to control temperature and pressure of a wildly fluctuating system such as a tyre and wheel, if you drop the pressure of a fixed volume it will only go back up again by the same mechanism... The problem is a thermal mass problem. If you can restrict the thermal mass of the air in the tyre you can put a cap on the maximum pressure it can produce and also the heat transfer to that mass of air - during the race.

Do not get distracted by the extra volume of the hollow spokes. In my shrewd view, this is not a volume or pressure problem, this is a mass and heat transfer problem.

[Xwang]

When is tyre pressure controlled during qualyfing?

[stevesingo]

Any one see how the new Technical Directive will change anything?

during practice sessions, qualifying and the race, "the minimum starting tyre pressures, as set out in the Pirelli preview for each event, will always be checked before the wheels are fitted to the car".

So from what I see, the teams have been pumping hot air in to the brake duct and brake system in order to heat the wheel rim, therefore generating the higher tyre pressures required on the start line.

What is stopping them heating the wheel rim off the car?

[hollus]

Nothing, but the rim has as little mass as possible, hence it stores little heat, and you can't go much above 110C before harming the rubber. so advantages will be more limited. Also, it is easy to ban extra devices "inside the wheel heater" if needed.

[bill shoe]

Any one see how the new Technical Directive will change anything?

during practice sessions, qualifying and the race, "the minimum starting tyre pressures, as set out in the Pirelli preview for each event, will always be checked before the wheels are fitted to the car".

So from what I see, the teams have been pumping hot air in to the brake duct and brake system in order to heat the wheel rim, therefore generating the higher tyre pressures required on the start line.

What is stopping them heating the wheel rim off the car?

The cryptically worded FIA announcement was hard to understand at first. They were trying to announce a solution to a problem without admitting the specifics of the problem.

I think the problem was that tire pressures were only being checked after the wheels were bolted on the cars. Brake heat and other thermal masses on the car were used to heat the wheels on the car and thus raise the temp & pressure of the contained tire air. Going forward the rules say the tire pressure must be checked before the tires are bolted to the car.

Rules already said the only part of the wheel/tire assembly that can be heated is the tire perimeter (tread area). No blatant/obvious heating elements to the sidewalls or wheels. So now you can still heat the internal air as a "trick", but you have to first put the heat into the tire via the perimeter with a tire blanket, and as Hollus mentioned if you heat the tread rubber beyond some point you damage it.

Or you have to figure out another clever way of discreetly heating the air in the tire before the FIA does the off-car pressure check.

[Nickel]

Could you not simply inflate the tire with heated air shortly before measurement takes place? I'm aware that compressed air is by default warmed from compressing it. Surely this could be exaggerated to some extent?