Jeep science fair project question

[pkrfctr]

My son is doing his science fair project on how lower tire pressure affects surrface area and helps with jeeping in sand/snow.
Trying to come up with a good way to measure the 'footprint' of the tires at various psi's. Any ideas? Thinking that jacking the jeep up and lowering it into/onto something and then measuring the print would work. But cant come up with anything decent.

 

[Jay5.9L]

Maybe use a small wheelbarrow or a bike tire and run it over almost cured plaster at different pressures. See if the foot print changes.

 

[Jay5.9L]

Or over clay, damn ploymetirc sand, etc

 

[TurboMinivan]

Drive slowly through a small puddle on pavement, then measure/photograph the tire mark left on the dry section.

 

[DAA]

Or maybe just drive onto or lower onto pieces of paper at the different PSI, I bet it would leave a clear imprint on the paper. Be cheap and also easy to transport for display. Could use some paint or something on the tread to spice it up, like finger printing. Or use something similar but more sturdy and nicer for display than plain paper. Thin cardboard or something like that.

- DAA

 

[smfulle]

Use a piece of chalk on the driveway to circle the the contact patch at different pressures. You could line them all up and take photos.

 

[Hickey]

Or maybe just drive onto or lower onto pieces of paper at the different PSI, I bet it would leave a clear imprint on the paper. Be cheap and also easy to transport for display. Could use some paint or something on the tread to spice it up, like finger printing. Or use something similar but more sturdy and nicer for display than plain paper. Thin cardboard or something like that.

- DAA

I think that's your ticket. Even cardboard would take the imprint well enough to convey the idea.

 

[Jinx]

I think that's your ticket. Even cardboard would take the imprint well enough to convey the idea.

Yep, at full pressure only the edge of the curb will show, as the pressure decreases more and more of the tread pattern will show on the paper as the tire bends/flexes around the curb.

 

[LJTim]

I would just make sure the tire was plenty dirty - rub a shop rag on it or something, then drive it straight across a white piece of paper.

 

[I Lean]

I bet some foam-core would show the footprint pretty well. Would sorta crush it's way in...

 

[Homefryy]

I like the idea of putting paint on the tire then lowering it onto a sheet of paper. Since it is for a science fair that would give you nice visuals to use.

If you wanted to complicate things you could put something on (or maybe under) the paper in the center of the tire like a rock or narrow piece of metal to show how tire pressure affects contact patch on an uneven surface.

 

[DAA]

I bet some foam-core would show the footprint pretty well. Would sorta crush it's way in...

Something like this would be cool. Built in area calculation.


https://www.amazon.com/Royal-Brites...51&sr=8-3&keywords=foam+board+with+grid+lines

- DAA

 

[pkrfctr]

The boys got started on this today. They aired down the tires, jacked up the jeep, sprayed the tire with tire shine foam and then lowered it down onto a piece of cardboard. It worked decent. The only thing I didnt like is they didnt get a great width measurement because the lugs would hold the sidewalls just high enough that they wouldn't mark the cardboard. If we were super gungho I think redoing it with an inch of sand in a cookie sheet would fix it. They then squared up the print by the widest and longest points and measured them up to find the square inches.
heres the numbers
My JK weighs 6240 LBS we did all the prints on the drivers rear tire
30 PSI = 102.5 sq in
12 PSI = 147 sq in
8 PSI = 180.63 sq in
4 PSI = 301.88 sq in
They then times that number by the four tires and divide by the weight of the jeep to figure out how much of the jeep weigh is on each inch of the contact patch.
30 PSI = 15.22 lbs per sq contact patch inch
12 PSI = 10.61 lbs per sq contact patch inch
8 PSI = 8.6 lbs per sq contact patch inch
4 PSI = 5.17 lbs per sq contact patch inch

 

[smfulle]

Those are interesting numbers.
And this is the most awesome science fair project ever!

 

[pkrfctr]

Those are interesting numbers.
And this is the most awesome science fair project ever!

thanks. They had to decide between this and some electrolyte drink thing, cant believe that was a decision........
should mention 40" mtr's
next step is to go to the sand dunes and 'high mark' each pressure for real world results. they'll take pics and video of each run and have that on the display board.

 

[pkrfctr]

Well they are 1 of 5 teams headed to district from their school.

 

[Mouse]

If they win an award you might send a note to Goodyear. Sometimes corporations like to recognize young engineering efforts.

 

[pkrfctr]

They took high honors at District and are headed to state. They actually beat the second and third place winners from their school at district. The only projects that did better were 9th graders who are in a different division at state.