What do the numbers on my car’s stickers actually mean?

225 is the section width in millimetres, 45 is the aspect ratio — the sidewall height as a percentage of that width — and 17 is the rim diameter in inches. So the sidewall is 225 × 0.45 = 101 mm tall, and the overall diameter is that twice plus the rim: 202 + 432 = 634 mm, about 25 inches.

It reads low by the same percentage the diameter grew, and the odometer undercounts by the same amount. A 3% larger tire means you are actually doing 62 mph when the needle says 60, and 100 recorded miles are really 103. That also inflates any mpg figure you calculate from the odometer.

The door sticker, always. The number moulded into the sidewall is the maximum pressure the tire can safely hold, not the pressure your car was engineered around. Inflating to the sidewall maximum gives a harsh ride, centre-band wear and less grip.

Air pressure falls roughly 1 psi for every 10°F drop in temperature. A tire set to 33 psi on a 75°F afternoon reads about 29 psi on a 35°F morning, which is enough to trip a system that warns at 25% below placard. Top up cold, in the morning, rather than after driving.

On dry asphalt with a one-second reaction time, roughly 240 feet in total: about 88 feet while you react and around 150 feet of actual braking. In the wet the braking part alone stretches past 240 feet, which is why the classic two-second following rule becomes four in the rain.

Because braking distance is proportional to speed squared while reaction distance is only proportional to speed. Going from 30 to 60 mph doubles reaction distance but quadruples braking distance. The same reason explains why a small speed reduction produces a disproportionately large safety gain.

Everything that is not the truck: driver, passengers, cargo, aftermarket accessories, and the tongue weight of any trailer. That last one catches people out — a 700-pound tongue weight consumes most of a half-ton pickup’s payload before you have loaded the bed at all.

GVWR is the maximum the truck itself may weigh, fully loaded. GCWR is the maximum for the truck and trailer combined. You can be under GVWR and still over GCWR, or the reverse — both limits have to be respected, and the axle ratings underneath them as well.

Start with what the owner’s manual specifies; that number already accounts for the starter, the compression ratio and the climate the vehicle was designed for. As a sanity check, roughly 300 CCA per litre of displacement for gasoline and double that for diesel gets you in the right neighbourhood, and 20% more is cheap insurance in a cold climate.

Two things happen at once. Cold thickens the engine oil so the starter needs roughly twice the torque, and cold slows the battery’s chemistry so it delivers around half its rated output. A battery that was marginal in October simply cannot bridge that gap in January.

Not exactly — it is 1.3558179483314 N·m, derived from three exact definitions: the avoirdupois pound (0.45359237 kg), standard gravity (9.80665 m/s²) and the international foot (0.3048 m). The difference from 1.356 is tiny, but tables that pair a rounded 1.356 with a rounded 0.738 for the reverse do not round-trip, and the error compounds on repeated conversions.

Passenger cars are typically 80–100 lb-ft, light trucks 100–140 lb-ft, but the manual is the authority and the spread is wide. Tighten in a star pattern with a calibrated torque wrench — an impact gun cannot be trusted for the final pass — and re-torque after 50 to 100 miles on newly mounted wheels.