A commonly taught safety rule is that a truck will take about 50% longer than a car to stop on a wet road.

Key idea in simple terms

  • Many driving-safety and quiz-style materials phrase it exactly this way:

A truck will take how much longer to stop on a wet road than a car?
and give “50% longer” as the correct choice.

  • In practical driving, the exact percentage can vary with speed, load, brakes, tyres and road surface, but the rule-of-thumb answer to that question is 50% longer.

Why trucks need longer

  • Trucks are much heavier, so at the same speed they need more distance to stop even in ideal dry conditions. For example, at 65 mph a car may need around 300–316 ft to stop, while a heavy truck can need roughly 525–600 ft, which is about 60–100% more distance.
  • On wet roads, all vehicles need more distance, but the heavier truck’s disadvantage becomes more significant, which is why teaching materials emphasise a larger “extra” margin such as 50% longer to keep drivers conservative and safe.

Mini FAQ

  • Is 50% an exact physics number?
    No; it is a safety rule of thumb , not a precise calculation. Real-world differences can be greater, especially at higher speeds or with worn tyres or heavy loads.
  • What should a driver actually do?
    Leave much more following distance behind trucks and in front of them in the rain, slow down, and assume they may need roughly half again as much distance as a car—or more—to stop safely.

So, for the specific question “a truck will take how much longer to stop on a wet road than a car?”, the standard answer is: 50% longer.

Information gathered from public forums or data available on the internet and portrayed here.