HOW CAN DAMP WEATHER AFFECT MY CAR’S BRAKING ABILITY?
                     HOW CAN DAMP WEATHER AFFECT MY CAR’S 
BRAKING ABILITY?
Mark Sanford
Writer at Brake System
University providing advice, reviews and information on 
brake system components including 
brake line repair kit advice at break system university/
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rsity
FRICTION
That is what is required to bring a moving vehicle safely to a halt. 
Rainwater and damp weather make surfaces more slippery. Understanding 
the concept behind each of these two statements will help you to 
understand the adverse effects that damp weather can have on your car’s 
braking ability.
Motor vehicle brake shoes and pads are configured primarily of a steel 
backing and a thick layer of friction material. Since these thick layers of 
friction material must remain porous in order to “bite” down (gradually) 
and stop the vehicle. The surfaces which they contact must remain 
exceptionally uniform and flat. If not, there will be unpleasant 
abnormalities in braking.
Although the flat and uniform surfaces of the rotors and drums (which act 
as a drag for the friction material on brake pads and shoes) can feel 
slippery to the touch, water and damp weather affect them very little as it 
pertains to braking ability. This is because of the extreme temperatures 
generated by rotating components as they lightly contact one another.
ROTOR AND DRUM SURFACE
One area in which water and damp weather will adversely affect rotor and 
drum surfaces (and braking ability) is anti-parallelism, warpage, cracking, 
and out-of-roundness. Long after the storm has passed, standing water on 
the roadway can create problems that affect your ability to brake 
effectively. When (and because) brake rotors and drums are extremely hot, 
contact with cool water may cause them to warp or crack in a variety of 
ways. Where brake rotors are concerned, variations in surface parallelism 
that exceed maximum allowable specifications will cause brake pulsations 
that are felt and seen in the steering wheel. Brake drums that are warped 
will contact the brake shoes unevenly and cause the rear of the vehicle to 
shudder when braking. This is usually felt in the seats and floor of the car. 
Neither of these conditions is terribly unsafe but they make the vehicle 
seem unstable at times
BRAKE FLUID
Another area where water and damp weather can adversely affect your 
car’s braking ability pertains to brake fluid. While water and damp weather 
will not have an immediate effect on your brake fluid, over time airborne 
moisture may contaminate your brake fluid master cylinder reservoir. Since 
brake fluid reaches extremely high temperatures, any water that is mixed 
within will boil. The small pockets of boiling water will create steam and 
cause air pockets in the hydraulic lines of the braking system. Vehicles in 
areas which experience above-average amounts of damp and rainy 
weather should have the brake fluid flushed and replaced annually.
Where damp weather and rain affect your vehicle’s braking ability the 
most actually has nothing to do with the brake system. Water, and 
especially standing water, on the roadway can affect your car’s ability to 
brake safely more than any other non-mechanical factor. Tires are your 
first line of defense against this wet hazard of the road. Tire maintenance 
and making sure that you have tires with sufficient tread and the correct 
amount of air pressure are critical to your braking ability in damp weather. 
When scheduling tire maintenance, add windshield wiper blade 
replacement. A good set of wiper blades can go a long way towards a safe 
drive.
DRIVING HABITS
Finally, let’s talk driving habits. Often the weakest link in the braking 
system is found between the steering wheel and the driver’s seat. 
Distraction is the enemy of safe driving. This is especially true in damp 
weather. Allow more distance for braking when the road surfaces are wet 
and dramatically increase the braking ability of your automobile. Avoid 
driving through standing water when your brakes are hot and you may 
avoid brake pulsation and the expense of premature rotor and drum 
replacement.
In summary, your best defense against the adverse driving conditions 
created by damp weather is to maintain the vehicle’s braking system and 
tires as recommended by the manufacturer and avoid distractions while 
driving especially in the rain.
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