PassDGTChapter 13 of 17 · 29 questions
Tire wear and pressure, chains and winter tires, braking distances and what affects grip. Expect questions on legal tread depth and on aquaplaning.
Always measure tire pressure when the tires are cold. Driving heats the air inside and raises the reading, so a warm or hot tire gives a false result. Use a pressure gauge, like a pocket gauge or the one at a gas station. Check often and before any long trip.
Wear in the center of the tread means the tire is overinflated. The middle bulges out and carries most of the load. Low pressure does the opposite and wears the edges, while correct pressure wears the tread evenly. Set the pressure, with the tires cold, to the value in the owner's manual or on the vehicle's label.
Underinflated tires have more rolling resistance, so your vehicle burns more fuel. They also wear unevenly, last less, and overheat from extra friction with the road, which can cause a blowout. Pressure clearly matters, and low pressure never saves fuel.
Fog doesn't just cut visibility. It also dampens the asphalt, making the road slippery and reducing your tires' grip. That's why both "no" answers are wrong. In fog, always adjust your speed to the conditions.
Wet brakes temporarily lose effectiveness. Braking force can drop, the wheels may lock, and the brakes may even stop working for a moment. Press the brake pedal lightly a few times to dry them out. They don't get better when wet, and they aren't permanently damaged.
Motorcycle tires must be in good condition, with no cuts, cracks, scrapes, or deformation of the tire or rim. Check them and their pressure often, since damage can cause a crash. The front and rear tires don't have to be identical, and the tread-depth figure isn't the general condition this question is asking about.
Shock absorbers are part of the suspension and keep the wheels in contact with the road. Worn shocks let the wheels bounce more than usual over potholes and bumps, which hurts stability and braking. If you notice this, have them replaced. The clutch and brakes don't control wheel bounce.
Slow down before reaching snow, water, or ice, then keep the bike upright and avoid leaning, turning, or braking on it. This keeps as much grip as possible. Speeding up or braking on the slippery patch can make the wheels skid.
Always inflate your tires to the pressure the manufacturer recommends. That figure is based on the tire size, the weight each axle carries, and how the vehicle handles. Choosing your own pressure or always going higher is incorrect.
Vehicles carrying people or goods with an MMA of 3,500 kg or less must carry a temporary-use spare wheel, a full-size wheel, or an alternative such as a puncture repair kit. So a temporary spare is allowed on this truck, not just on cars, and a full-size wheel isn't required.
Tires heat up as you drive, and warm air raises the pressure. The manufacturer's recommended pressure is for cold tires, so wait until they cool before checking. Don't let air out of hot tires, or they'll be underinflated once they cool.
Stay calm and keep the engine running. Lift off the gas and shift down gradually so the engine slows you to a stop. Yanking the parking brake can make you skid, and hitting an obstacle is a last resort, not the correct response.
On a wet road, braking hard without ABS can lock the wheels. You then skid, need a longer distance to stop, and lose steering control. Worn tires make this worse but aren't the danger of braking itself, and wet roads are never risk-free.
Brake hoses have no set replacement interval, so you need to inspect them to spot problems early. Check that they're clean and free of cracks and leaks. They do deteriorate, and a damaged hose can cause brake failure even if the fluid is in good condition.
Age, use and weather make tire rubber harden and crack, so it loses its grip on the asphalt. With less grip, the vehicle can skid on any surface, not just wet roads. Hardened rubber never grips better.
The extra weight presses the wheels harder onto the road, so they lock later and less easily when you brake, especially the rear wheel. The extra weight also makes your braking distance longer, not shorter. Your reaction time depends on you, not on carrying a passenger.
Tires usually expire about 5 years after they are made, because the rubber loses its elasticity and no longer grips the road properly. There is no fixed mileage like 5,000 km for replacing them. Any cuts, cracks or bulges also mean you must replace the tire, whatever its tread depth.
Water can make your brakes temporarily lose effectiveness, so check them first once you are out of the water. Press the brake pedal gently a few times to dry them so they gradually recover. Water does not normally affect the shock absorbers or steering in this way.
You are not required to carry a spare wheel for a trailer. This applies to both heavy trailers and light trailers (maximum authorized mass of 750 kg or less). So neither "yes" option is correct.
Braking distance runs from the moment the brakes actually start working until the vehicle comes to a complete stop. The distance from seeing the obstacle to braking is the reaction distance, and the two together make the stopping distance. Braking distance depends heavily on the condition of your brakes and tires.
Taking a sharp left-hand curve too fast creates a strong sideways force that makes the tires slip outward, so your vehicle may veer to the right, not the left. Good signs do not remove this risk. To control the skid, press the clutch to cancel engine braking and quickly turn the steering wheel in the direction of the skid (countersteer).
A load adds weight, and a heavier vehicle needs more distance to stop once you press the brake pedal. So a loaded vehicle's braking distance is always longer than the same vehicle's when empty. The load clearly affects it and never shortens it.
Very hot asphalt makes the tread heat up more than normal from friction, which can increase tire wear by about 25%. So heat never reduces wear. Overinflated tires also wear the tread faster than usual.
Flashing the brake lights repeatedly warns drivers behind that you are about to slow down considerably, for example because of a breakdown or a traffic jam, especially on a freeway (autopista) or divided highway (autovía). It does not tell you to use the shoulder or give a distance to a jam. Turn signals or arm signals should not be used for this warning.
Braking distance is how far your vehicle travels from the moment you press the brake until it stops completely. It depends mainly on the vehicle and its load (for example, shock absorbers and tires), the road surface and how well the tires grip it, and your speed. Since several factors are involved, answers saying it depends 'only' on one thing are wrong.
ABS stops the wheels from locking when you brake hard, so you can still steer while braking. It does not steer the vehicle for you. It also does not always shorten braking distance; on surfaces like gravel or snow, it can even make it longer.
Check your tire pressure once or twice a month, and also before a long trip, always with the tires cold. Warm tires give a higher, misleading reading. Checking only before long trips is not often enough.
Use, weather and age make tire rubber harden and crack, so it grips the road poorly. This can make you skid on any surface, not only a wet one. Hard rubber does not grip better; it grips worse.
Worn or damaged tires grip the road less, so the car takes longer to stop and the braking distance grows. Braking distance is not fixed and does not depend only on speed. It also depends on the tires, the brakes and the road surface.