Tire Question - Page 2 - GreenHybrid

worthywads · #11 (**permalink**) 02-09-2006, 05:27 PM

Quote:

Originally Posted by gpsman1

Question #2
Which weighs more, a tire filled with Helium, or an empty tire?

Answer: The tire filled with Helium weighs more, as a tire filled with something, must weigh more than a tire filled with nothing.

The trick would be filling a tire with nothing, a tire with nothing in it has been evacuated with extreme suction and probably has never been done.

tigerhonaker · #12 (**permalink**) 02-09-2006, 06:59 PM

I'm Like So Very Educated now on this Weigh Tire, Full/Empty Thing Thread.

I Think I am-I Think I am-I Think I am-I Think I am-I Think I am.

Thinking This Over

Terry

HypoMiler · #13 (**permalink**) 02-09-2006, 09:18 PM

A very expensive pressure transducer (and I don't mean AutoZone vs. Walmart tire gage) would show a difference between the loaded and unloaded tire. The unloaded tire has a bit higher volume -- it expands to the shape where pressure is mimimized. Any change in shape from this means a lower volume, thus slightly higher pressure. This is insignificant compared to the change in footprint that accompanies the deflection under load. Weight on tire [force] = Pressure [force/length^2]*Contact_Area [length^2] in any consistent units.

The US Olympic cycling team was sure they were going to win big because they had the technological edge, including the 'right' gasses in their tires. Their results said they should have spent the time training. The winners probably had ordinary air in their tires... but you can bet that the tires were pumped up that morning.

gpsman1 · #14 (**permalink**) 02-09-2006, 11:12 PM

Not to beat a dead horse.. But....

Modern car tires can change shape, but not size.
I actually measured.
The tire acts like a leather belt, not like a rubber balloon. It can come close to a circle with lots of pressure ( or no load ) or it can be like a tank tread, with low pressure and lots of load.

A Ford Escape Tire with 48psi and loaded = 2100mm perimeter. ( not a circle )
A Ford Escape Tire with 48psi off the ground = 2100mm circumference.

A Ford Escape Tire with 35psi and loaded = 2100mm perimeter.
A Ford Escape Tire with 35psi off the ground = 2100mm circumference.

A Ford Escape Tire with 20psi and loaded = 2100mm perimeter.
A Ford Escape Tire with 20psi off the ground = 2100mm circumference.

This came up on another group, and there were lots of theories, so I measurerd.
You can't say this is due to the "steel belt" because "radial" tires mean the belt goes accross the tire ( sidewall to sidewall ) NOT around the tire. Bias tires have the belt going around the tire circumference. Bias tires do not hold up as well.
Radial tires can spin either direction, so you can rotate left & right. ( or X )
Bias tires always have to spin the same way, so you can only rotate front to back.

- John

livvie · #15 (**permalink**) 02-10-2006, 07:10 AM

Quote:

Originally Posted by Adam_HybridCivic

40 psi means 40 units of pressure per square inch(not that you didn't know that), therefore the air inside the tire is exerting 40 psi against the walls of the tire. When the car is then put under load or sat to the ground the amount of pressure in the tire does not change. However, the shape of the tire that holds the air changes shape still exerting 40 psi. When the tire is under load however, it must have more air in the tire to keep the same `shape when not under load.

Thank you. That makes sense.

Adam_HybridCivic · #16 (**permalink**) 02-10-2006, 11:17 AM

Quote:

Originally Posted by gpsman1

Not to beat a dead horse.. But....

Modern car tires can change shape, but not size.
I actually measured.
The tire acts like a leather belt, not like a rubber balloon. It can come close to a circle with lots of pressure ( or no load ) or it can be like a tank tread, with low pressure and lots of load.

A Ford Escape Tire with 48psi and loaded = 2100mm perimeter. ( not a circle )
A Ford Escape Tire with 48psi off the ground = 2100mm circumference.

A Ford Escape Tire with 35psi and loaded = 2100mm perimeter.
A Ford Escape Tire with 35psi off the ground = 2100mm circumference.

A Ford Escape Tire with 20psi and loaded = 2100mm perimeter.
A Ford Escape Tire with 20psi off the ground = 2100mm circumference.

This came up on another group, and there were lots of theories, so I measurerd.
You can't say this is due to the "steel belt" because "radial" tires mean the belt goes accross the tire ( sidewall to sidewall ) NOT around the tire. Bias tires have the belt going around the tire circumference. Bias tires do not hold up as well.
Radial tires can spin either direction, so you can rotate left & right. ( or X )
Bias tires always have to spin the same way, so you can only rotate front to back.

- John

John, very good experiment to display what I explained eariler! Good job pointing out about radial tires as well, a should have said something about that as well.

HypoMiler · #17 (**permalink**) 02-10-2006, 08:04 PM

I'll beat the dead horse. Take the non-stretching leather belt, and make a circle. This represents the cross section, not the perimeter of the tire. Now flatten the circle. The enclosed area changes. For all practical purposes, though, the pressure can be assumed constant (other than what is due to temperature changes).

But the next question is, what constitutes the contact area? Does the area between the treads count?