What is the purpose of a tire's tread?

Tire tread: the patterned rubber that contacts the road. Functions: (1) CHANNELS WATER away from the tire-road interface, preventing HYDROPLANING (tire riding on top of water film); deeper tread = more water displaced; (2) PROVIDES MECHANICAL GRIP on irregular surfaces (gravel, snow, ice, off-road); tread blocks bite into irregularities; (3) DISSIPATES HEAT from rubber working against road; (4) GENERATES NOISE-MASKING patterns (good designs minimize road noise); (5) REDUCES ROLLING RESISTANCE through optimized contact area. Tread depth: new tires typically have 10/32 to 12/32 inch tread depth; legal minimum: 2/32 inch in most US states (when wear bars are flush with tread surface); 4/32 considered prudent minimum for safety in wet conditions; 6/32 for winter conditions. Tread wear indicators (WEAR BARS): small raised bars between tread blocks; become flush when tread reaches 2/32. Penny test: insert penny upside down into tread; if Lincoln's head is fully visible, tread is 2/32 or less (replace); quarter test: Washington's head fully visible = 4/32 or less. Tire types: (1) ALL-SEASON — compromise design; good for most conditions except deep snow/ice; most common original equipment; (2) SUMMER/PERFORMANCE — softer rubber, optimized for dry/warm; poor cold/snow performance; (3) WINTER/SNOW — siped (small slits) tread blocks, soft rubber compound that stays pliable in cold; symbol: snowflake-and-mountain peak; significantly better cold/ice traction; wear faster on dry warm pavement; (4) ALL-TERRAIN/MUD-TERRAIN — aggressive tread for off-road; noisier on pavement; (5) TOURING — comfort, longevity; (6) HIGH-PERFORMANCE — sport handling, shorter life. Tire markings: P (passenger), LT (light truck); WIDTH (e.g., 215); ASPECT RATIO (sidewall height as percentage of width, e.g., 60); CONSTRUCTION (R for radial); WHEEL DIAMETER (e.g., 17); LOAD INDEX (numerical, weight capacity); SPEED RATING (letter, max speed for sustained operation: S=112 mph, T=118, H=130, V=149, W=168, Y=186). Example 215/60R17 95H: 215 wide, 60% aspect ratio, radial, 17-inch wheel, 95 load index (~1521 lbs), H rated (130 mph). MAINTENANCE: (1) PRESSURE — check monthly when cold; follow placard in driver's door jamb (not the tire sidewall, which shows MAX pressure); underinflation increases rolling resistance, wear, and overheating risk; overinflation reduces contact, increases harshness; modern TPMS warns at 25% low; (2) ROTATION — every 5000-7500 miles; promotes even wear (front tires wear faster, especially on FWD); typical patterns: front-to-rear straight (non-directional), front-to-rear with side swap, X-pattern; (3) ALIGNMENT — when uneven wear noticed; (4) BALANCE — when vibration; weights added to wheel; (5) AGE — replace tires older than 6-10 years even with good tread, as rubber degrades; check DOT code (last 4 digits = week/year of manufacture). HYDROPLANING: tire rides on water film; loss of traction and steering control; minimize by: maintaining tread depth, slowing in heavy rain, avoiding standing water; if happens: don't brake or steer hard; ease off accelerator until traction returns.