Water on the road creates a thin film between your tyres and the tar, reducing the friction your brakes rely on to slow the car down. Depending on tyre condition and road surface, braking distance on a wet road can be significantly longer than on a dry one at the same speed — and in the first few minutes of rain, roads can be even more slippery as oil and dust rise to the surface before being washed away. This is why defensive driving recommends easing off the accelerator earlier, increasing following distance, and braking more gently and progressively in wet conditions rather than relying on hard, late braking the way you might on a dry road.
Source: Arrive Alive Road Safety Initiative
Frequently Asked Questions
Why are the first few minutes of rain the most dangerous?
Light rain lifts oil, dust and rubber residue off the road surface before washing it away, creating an especially slippery film until heavier rain rinses it clean.
Should I brake differently in the rain?
Yes — brake earlier and more gently rather than late and hard, since a wet road gives your tyres far less grip to work with.
Do worn tyres make wet-weather driving more dangerous?
Significantly so — tyre tread channels water away from the contact patch, and worn tread can't do this effectively, increasing the risk of aquaplaning.
How much extra following distance should I leave in the rain?
Many instructors recommend at least doubling your normal following distance in wet conditions to account for the longer braking distance.