Tire Contact Patch from Load and Pressure
The tire footprint, and the flotation lever behind airing down.
Example
You enter
- Corner load W (lb) 900
- Inflation pressure p (psi) 35
You get
- Contact area (in²) 25.71
- Contact area (cm²) 165.9
Checked against published worked examples from: Boeing Commercial Airplanes.
Details, formula, and sources
ScopeA = W / p, the corner load divided by the inflation pressure. Because the patch carries the load at the inflation pressure, the average GROUND pressure roughly equals the tire pressure independent of load -- which is why airing down floats over sand and cuts soil compaction. A 900 lb corner at 35 psi rides on about 25.7 in^2; drop to 15 psi and the patch grows to 60 in^2 (2.3x) at the same load. An idealization -- the sidewall and tread carry a little load, so the real patch runs a bit smaller than W/p, more so at high pressure. A field estimate, not a measured footprint; the tire, load, and surface govern.
Formula or tableA = W / p; A_cm2 = 6.4516 A. Average ground pressure ~ p.
Source and editionThe first-order tire contact-patch relation A = W / p (ideal air-pressure membrane), first-principles; the tire, load, and surface govern.
Free accessThe load = pressure x area relation for a pneumatic tire is a standard first-principles estimate; the load and inflation pressure come from the vehicle.
What governsEstimate. AHJ and licensed professional govern.
API field namescorner_load_lb, inflation_pressure_psi, contact_area_in2, contact_area_cm2
- Ideal membrane W = p x A; the patch carries the load at the inflation pressurepneumatic-tire first principles
- Ground pressure average ground pressure ~ inflation pressure, independent of loadthe A = W/p relation
- Idealization sidewall/tread stiffness make the real patch a bit smaller than W/pscope of this tile