Talk:Caterpillar track
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- ...Christie suspension uses oversized road wheels and the track simply lies on top of the wheels. The shape of the track as a whole is somewhat banana-like as the track droops onto the wheels after running over the driving wheel and idler.
- Chinese Type 62 tank with "Christie" tracks. The driving-wheel is in the back.
This is incorrect. Christie suspension has coil springs inside the vehicle's hull, and was generally replaced by torsion-bar suspension. The Christie designs also used a different method of driving the tracks, and some had a chain drive which could be engaged to run the road wheels, so the tracks could be removed for road travel ("convertible" tanks).
The Soviets abandoned convertible drive after the BT series, adopted torsion-bar suspension in the T-44 and drive sprockets in the T-54. The pictured Chinese tank is a T-54 derivative, which has a torsion-bar suspension and conventional rear drive sprocket. It is in no way Christie.
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[edit] Crimean War
Steam powered tractors using a form of caterpillar track were reported in use during the Crimean War in the 1850s.
- Reported?? Any more info on this?KAM 00:21, 2 November 2005 (UTC
- I agree that there is evidence of a report. What I should have asked is if there is evidence of the use of tracked vehicles in the Crimean War? Surely they would have left more of a trace then mention on a TV show's web site.KAM 15:02, 14 April 2006 (UTC)
[edit] Live/dead track, slack track
An anonymous editor recently wrote the edit summary ""Dead track" refers to dry pin tracks, vs "Live track" where the rubber bush causes the link to spring back to a designed angle, return rollers are irrelevant." If this is technically correct, then wouldn't it be the case that live track would not lie slack, so that dead track often corresponds with slack track? It's quite common in a military context to treat the two as a synonym, even though they may not be technically the same. —Michael Z. 2006-02-1 16:25 Z
- It's complicated. Dead track/live track is fairly simple. With dead track the links are joined by a ordinary steel pin, it functions just like a door hinge, move it to a certain angle and (absent any other forces) it stays there. German, british and soviet tanks of WWII and most construction equipment uses this type. American and most post war western tanks use live track, the pin (well not always a pin) is bonded into the link with rubber, it's springy enough that you can still bend it (or at least the vehicle can) but when the load is taken off it the rubber rotates it back to it's original angle, usually slightly curled up. If you hunt around on the net you can find pictures of Shermans and such where if the track is broken the last few links will actually be held up off the ground because of this.
- Now whether you use return rollers or not is a whole other matter T34/Panther/Crusader all dead track, none with return rollers. Centurion/Comet/Stalin all dead track, all with return rollers. Abrams/Leopard/FV423 live track, with return rollers. The M113 uses live track but doesn't have return rollers but I can't think of another that does off the top of my head right now (M551 Sheridan and the FV101 Scorpion might but I'm not sure). The trend is towards the live track/return rollers since you can have more smaller road wheels to distribute the weight of the vehicle, and the rubber bushs extend track life since they eliminate metal on metal contact between the pin and link.
[edit] Ground pressure
"the ground pressure of a car is equal to the pressure of the air in the tires, perhaps 30 psi (207 kPa)" Is this right? A bicycle has pressure of 100 psi or more with or without a rider yet a bicycle with a rider will obviously sink deeper then a bicycle being pushed. What am I missing? KAM 18:04, 7 May 2006 (UTC)
- There are two ways a tire can increase its ground contact area in response to increased weight. One is for the tire to flatten out until the contact area compensates for the increased weight. The other is for the tire to sink into the ground until the contact area compensates for the increased weight. The shape of the tire and the hardness of the ground determine how much of each factor is involved. For car tires on pavement, flattening accounts for almost all of it: try lifting up a car on a jack, and watch how the shape of the tire changes. For bicycle tires on mud, sinking accounts for most of it. --Carnildo 21:25, 7 May 2006 (UTC)
The above statement "the ground pressure of a car is equal to the pressure of the air in the tires, perhaps 30 psi (207 kPa)" is totally incorrect. The ground pressure of a car is the weight of the car divided by the contact area of the tires. For example, if a car weighs 3000 lbs and each tire has a contact area of 4x6 inches, that would equate to 3000 lbs/(4x6)x4 or 31.25psi. This is simplified because the front and rear tires are likely to have different amounts of weight on them, but for this example, it is sufficient. You can actually reduce the ground pressure by reducing the pressure in the tires and increasing the contact area of the tires.
- That at least implies that ground pressure has a positive relationship with tire pressure. I've also read somewhere that tire pressure=ground pressure—we need a reference to resolve this. —Michael Z. 2006-10-11 17:15 Z
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- The tire works in a pretty simple way. First, there is zero-load pressure, provided by tire elasticity. When the wheel is under load, it deforms (flattens in the contact area), thus decreasing the volume and correspondively increasing the pressure. For a vehicle to retain zero vertical acceleration, the vehicle weight must equal the upward force exerted by the pressurized air inside the tire. So a car actually floats on air, which pressure changes with the car's weight.
- If we view the Ground-Wheel system, then the tire itself is just a membrane. Pressure on ground is exerted by the air pressure in the tire. So tire pressure doesn't just equal ground pressure - it's simply the same thing. When you measure the pressure of tires on the ground and the pressure inside the tires, you measure the same thing; tires themselves don't exert pressure, it's the air inside what does. CP/M comm |Wikipedia Neutrality Project|
- The ground pressure of a car tire is exactly equal to the air pressure in the tire (give or take the stiffness of the tire material). This is elementary physics -- you should be able to get it from a textbook. --Carnildo 05:32, 15 October 2006 (UTC)
- I suspect that it is true that in most cases air pressure and ground pressure are nearly equal. It is not equal at low pressures and low vehicle weight because some weight is supported by the tire wall as has been pointed out. My guess it that it also does not hold true with low vehicle weight and very high pressure, the example of the road racing bike at 20 lbs weight and 100 psi. In this case the the some of the increase in contact area is due to the rubber deforming. Consider a small steel container (a compressed air tank) with 100 psi air pressure placed on the ground. Only the weight would be considered, not the air pressure inside. On the other hand it seems the weight/contact calculation will always be right. A source would be nice otherwise we are guilty of doing our own research. KAM 13:48, 19 October 2006 (UTC)
[edit] OR
I've tagged this article OR, mainly because of its total lack of references, but specifically because the part about why tank tracks may be undesirable seems very speculative to me. mgekelly 12:02, 27 June 2006 (UTC)
- just delete it citeing OR - it appeared in one huge block by an unregistered user. Alternatively trim it down to a single short paragraph. GraemeLeggett 13:01, 27 June 2006 (UTC)
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- Trimmed most out. GraemeLeggett 10:46, 5 July 2006 (UTC)
[edit] General track term
I think that it would be useful if an encompassing track title could be used at the top of the explanation of tracks. Currently, pages such as Track link here (to caterpillar track), implying a false specificity that excludes belt tracks. Perhaps Track (motorized), could be used to cover all types of tracks, or a better title if anyone can think of one. ENeville 05:16, 12 October 2006 (UTC)
- Crawler-tread? Track (crawler)? ENeville 05:19, 12 October 2006 (UTC)
