What specific mechanism/parts of a tire are actually the part that is carrying the "load". I believe I know the answer but have been surprised that I cannot find a single relevant hit thru Google. I don't want to say what I think does it and bias anyone. Everyone I've asked about this seems to come away scratching their head.
Anyone here think they can elucidate something?
Ashton Crusher wrote in news: snipped-for-privacy@4ax.com:
I think it's air pressure combined with the fact that tires are essentially inextensible.
Since the tires have a fabric carcass that prevents the tire from expanding past a certain point, compression at one portion (the part that touches the road) cannot be offset by expansion at another (the part that does not touch the road), assuming sufficient pressure is present in the tire. This inability to expand allows air pressure to force the road wheel into the center of the air mass.
The air in the tire.
Ok, a couple answers but not detailed to the point I'm interested in. It seems to me that it's the top of the tire that holds up the bead ring, which in turn holds the wheel up. The bottom part of the tire does nothing but contain the air and the sidewalls on the bottom hold up almost none of the load, the sidewalls on top are what's holding things up. Would be easier to draw. I'm still looking for any thoughtful comments on this theory as there seems to be no googlable info on it.
Ashton Crusher wrote in news: snipped-for-privacy@4ax.com:
the actuall weight of the car is held up by the sidewalls and the bottom tread, the air only acts to keep the tire round, gravity always pulls down thereby exerting the pressure in the downward direction. KB
As far as "carrying" the load, it is mostly the pressurized air. However, that does not mean that any tire can be used with any vehicle, no matter how heavy. Using a tire beyond its load rating causes a lot more flexure of both the tread area and the sidewalls, heating them. This will contribute to failure. Additionally, the side load when turning will be higher in a heavier vehicle, hence increasing stresses mostly in the side walls, but also actually stressing tread higher too. This is not good for tire.
The reason for the higher flexure on an overloaded tire is that the contact patch must be larger at the proper inflation pressure. Again, since MOST of the support is air pressure, the air pressure times the contact patch area times the number of tires approximately equal the weight of the vehicle. With the same tire pressure, a heavier load means larger contact area.
Ashton Crusher wrote in news: snipped-for-privacy@4ax.com:
I see what you're getting at, and there's something to it, from what I can see.
You're thinking of the sort of phenomenon seen on a bicycle wheel, where the hub really does "hang" from its upper spokes. The upper spokes are under tension, and the lower ones are under compression. Grab a set of cutters and snip the upper spokes, and the hub will fall down.
However, a pneumatic tire has an additional force acting on it that a bicycle wheel does not. While a bicycle wheel encounters only the force of gravity, a pneumatic tire has two forces acting on it: gravity and air pressure.
As I stated before, a tire is inextensible. Air pressure acts in all directions, unlike gravity which only acts in one direction. The effect of air pressure above atmosphere on an inextensible tire is to push the wheel to the center of the air mass within the tire. The more pressure, the greater the tendency to push towards center of mass.
If you now introduce some unidirectional force (such as gravity, or the roller on a Hunter tire mounting machine) pressing radially against a point on the perimeter of the tire, air pressure and inextensibility will oppose this radial force, and the tire will "hang" from the portion of the sidewall opposite the unidirectional force.
However, should air pressure in the tire decline to closer to atmospheric, this unidirectional force will be more easily able to deform the inextensible tire to the point that, given low enough pressure differential, the perimeter will eventually contact the wheel rim and you will have a "flat".
The upshot of all the foregoing is that sufficient air pressure inside the inextensible tire is what allows the tire to "hang" from the portion of the sidewall that is opposite the unidirectional force. Absent inextensibilty and air pressure, the "hanging" phenomenon will have no useful effect.
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