A and N Photography: 2005 Tacoma with Wrangler Silent Armor Tires

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Analysis of Goodyear Wrangler Silent Armor tires on a 2005 Toyota Tacoma for sand
February 16, 2007

What tire pressure should one use while driving in sand with Goodyear Wrangler Silent Armor tires (265-70R16) on a 2005 4 door Toyota Tacoma 4x4?

The below figures are tire prints from the right rear tire with nothing in the bed. I used balsamic vinegar as an ink. The tire footprint was so large on the 5, 7.5 and 10psi pressures that an 11x14 piece of paper was necessary to capture the whole print. The jack was completely separated from the axle to ensure a complete contact patch. The prints are on a 1 inch grid.

Figure 1: 5 PSI

Figure 2: 7.5 PSI

Figure 3: 10 PSI

Figure 4: 12.5 PSI

Figure 5: 15 PSI

Figure 6: 20 PSI

Figure 7: 25 PSI

Figure 8: 30 PSI

Figure 9: 35 PSI

Figure 10: 40 PSI

Figure 11: Wheel height (inches) above ground as a function of tire pressure

Figure 12: Contact patch area (square inches) as a function of tire pressure

Tire PSI	Contact Area (sq in)
40	26
35	28
30	34
25	40
20	45
15	53
12.5	61
10	68
7.5	79
5	91

Table 1: Tire contact area versus tire pressure

Tire PSI	Tire Height (inch)
40	6.125
35	6.0625
30	6
25	5.9375
20	5.75
15	5.5625
12.5	5.375
10	5.1875
7.5	4.875
5	4.4375

Table 2: Tire height vs tire pressure
Discussion

It is interesting to note that the contact patch of the tire does not double until the pressure is reduced from 40 PSI to 15 PSI. When off-roading in sand, 15 PSI is the maximum I run at, depending on the conditions I expect to encounter. If there are hard areas and rocks to be driven over, 15-17 PSI is my standard, otherwise serious sand dune driving calls for 10-15 PSI. Some people have written that they run below 10 PSI. However, these same people are also running larger than stock tires, giving increased clearance.

Another thing to note is that when you are running aired down tires, you do not want to be driving fast for two reasons. The first is you may hit something fairly hard and damage your tire or your wheel, as you are effectively running on flattened tires. The second consideration is that the sidewalls are flexing a great deal more than when driving at street pressure. This dramatically increases the heat in the tires, the primary damage source for all tires. Treat the gently and they will take you to amazing places.

Disclaimer - If you go use this data and damage your truck, your self or something else, either following my methods or not, it's your fault. I make no guaranties, implied or otherwise, for what I did on my Tacoma. This article only relates my experiences has nothing to with what you may or may not experience. You have been warned.

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