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Just curious if we could

Discussion in 'Center Of Gravity' started by cybrfire, Sep 1, 2004.

  1. cybrfire

    cybrfire 1 ton status Vendor GMOTM Winner

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    Is there a way to put together a formula of some type where you can input tire size, weight of the vehicle and air pressure of the tire and calculate the footprint size and corresponding contact pressure?

    Would be nice if there was a way to put factual numbers or some type of data with a particular setup for compairson. Maybe some of you computer gurus can work something out and there should be enough folks on here that can measure contact patches to get a good start. I don't know just a thought.
     
  2. az-k5

    az-k5 1/2 ton status

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    It can be done. It is a pretty simple spreadsheet to make after the data is collected. But it doesn't give much info as to the ability of a tire. Seat of the pants feel is best for air pressure. I guess a comparison of tires and sizes would be nice so you could have an idea of what a tire would behave compared to others.

    PS not too sure if this is totally COG stuff but I will wait for Russ on that as this may very well create enough tech to stay.
     
  3. Resurrection_Joe

    Resurrection_Joe 1 ton status

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    That would be a lot of data to gather for each specific make of each tire in each configuration with certain tempurature and certain wear amount
     
  4. cybrfire

    cybrfire 1 ton status Vendor GMOTM Winner

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    I guess I was thinking less about how a tire would behave and more along the lines of weight distribution for a given tire. What got me to thinking about the whole thing is my friends samurai. He says he can drive over this and that and its because of the weight or more accurately how much contact pressur per inch. So if you cut and hack the hell out of a k5 and it has bigger tires is it possible to get it to float like a samurai? Don't know but it would be a valuable tool for all of us. If somebody is willing to put the formula together I can give two tires information.
     
  5. Sandman

    Sandman 3/4 ton status Author

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    I wonder if you could just pull a relational shortcut?

    Say...(the weights are tire stuff is just guesses)

    The Sammy weighs 2,500 pounds and the tire contact area is 20 square inches. So with four tires we have 31.25 pounds on each square inch of surface area.

    (2,500 pounds / 20 square inches)/ 4 tires = 31.25 pounds per inch


    I guess the idea would be to try to match the square inch weight load.

    So, on a 5,500 pound Blazer....

    (5,500 pounds)/(31.25 pounds per inch * 4 tires)= 44 square inches per tire.

    So then.....

    (44/31.25) - 1 = .408 or 41% increase needed in tire area.

    So for fun. Lets say that a 31" tire at full pressure gives you the 31.25 inches of tire contact. 31" * 1.41 is about a 44" tire.

    Now this does not include air pressure or lug style or a ton of other things like maybe just airing down a 36" tire can get you what you need.

    But it might be safe to say that you would need 40% more tire contact to get the same amount of flotation on the snow.
     
  6. cybrfire

    cybrfire 1 ton status Vendor GMOTM Winner

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    That's probably the easiest way to do it. I think I might go out tonight and jack both rigs up and make a tire print on a big sheet of paper and see how big a 33 is and how big a 44 is just for the hell of it. Start throwing some numbers around and see what I come up with.

    Biggest problem with this idea is the rim would effect the tire foot pring and air pressure and there are so many variables and all of them could make a significant difference.

    I just appreciate the value of factual data as opposed to guesstimation.
     
  7. PJTPW

    PJTPW 1/2 ton status

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    What I do is let air out of the front and rear tires in 1 lb increments, and measure the contact patch and ground clearance at each. I roll the truck back and forth between measurements so they're accurate. When the contact patch is not substantially increasing, you're pretty much just losing ground clearance, and you've reached the point of diminishing returns in most terrain.

    Ryan
     
  8. Sandman

    Sandman 3/4 ton status Author

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    [ QUOTE ]
    So for fun. Lets say that a 31" tire at full pressure gives you the 31.25 inches of tire contact. 31" * 1.41 is about a 44" tire.


    [/ QUOTE ]

    I dont like this one. that means a 44" tire with the same width as a 31" tire. So lets try again.

    31" tire * 10.5" wide * 1.41 = Tire Size * Tire Width

    So you would need a 31" by 15" tire to make up the difference.

    Or a 37" by 12.5" tire.

    Not as bad.
     
  9. cybrfire

    cybrfire 1 ton status Vendor GMOTM Winner

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    Guess I need to measure some tire patches tonight and see what's what. I'm almost starting to think that my 5?00 lbs. blazer may distribut weight over more of a surface than that little sammy. Wouldn't that be bizarre.
     
  10. jimmy88

    jimmy88 1/2 ton status

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    Don't forget about the tread vs void area. There was a article in one of the 4 x 4 rags a while back talking about traction and contact pressure. Contact pressure will depend on the surface the tire is on and the tire tread. On hard surfaces, only the tread touches the ground so that is the area you need to divide into the load being carried. For soft surfaces the entire contact patch area carries the load. So with the same size tires on a hard surface, the one with the most open tread will have highest contact pressure, while in sand they will all be about the same.
     
  11. cybrfire

    cybrfire 1 ton status Vendor GMOTM Winner

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    Pretty much talking about flotation in soft terrain whether it be snow, mud or sand.
     

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