About how long is brake lag in a properly maintained air brake system?
Saskatchewan Commercial overview
Saskatchewan Commercial: Air brakes: who needs the A endorsement and braking principles
When the A endorsement is required, heat, friction and traction, how weight and speed change braking power, leverage and air pressure, and the three parts of stopping distance.
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- Topic drill
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Study reference: SGI Air Brake Manual (2025-26), Ch. 1 Requirements for A Endorsement and Ch. 2 Brakes and braking — Heat, energy, traction, friction, Speed, weight, distance, Stopping distance
All 11 questions in this test
Every question and its answer choices. The correct answers and explanations appear when you take the test above.
About how long is brake lag in a properly maintained air brake system?
- About 4/10 of a second
- About 1 1/2 seconds
- About 2 seconds
- About 1/100 of a second
At about what temperature do most brake linings work best?
- Around 250 °C
- Around 30 °C
- Around 120 °C
- Around 300 °C
If both the weight and the speed of a truck are doubled, how much more stopping power is needed?
- Eight times as much
- Sixteen times as much
- Four times as much
- Twice as much
One wheel's brake is poorly adjusted. What happens to the other brakes?
- They lock up at the first application
- They release slightly to balance the load
- They do more than their share and may overheat
- They keep working exactly as before
How must the practical air brake demonstration be done?
- Unassisted, without a checklist, on your own equipment
- With the examiner reading out each step for you to follow
- With a written checklist you bring along
- On an SGI-owned training simulator
Air at 120 psi acts on a 30 square inch diaphragm. How much force does it produce?
- 3,600 lb.
- 36,000 lb.
- 360 lb.
- 150 lb.
What determines how much heat a brake drum can absorb?
- The width of the tire tread
- The colour of the drum paint
- The thickness of the metal
- The length of the slack adjuster
A truck has hydraulic brakes with an air-powered assist. Do you need an A endorsement?
- Only if the truck has three axles
- Only for trips outside Saskatchewan
- No, air-over-hydraulic brakes are exempt
- Yes, any air component at all requires it
What is the final factor that determines whether a vehicle stops?
- The thickness of the brake linings
- Traction between the tires and the road
- The size of the brake chambers
- The air pressure in the reservoirs
Which driver does not need an air brake A endorsement?
- A city transit bus driver
- A school bus driver with an S endorsement
- A tractor-trailer driver on a highway
- A farm-licensed Class 3 truck driver
Stopping distance is made up of which three parts?
- Reaction time, brake lag and braking distance
- Speed, weight and tire pressure
- Brake fade, brake lag and road surface
- Following distance, reaction time and gear
Air brakes: who needs the A endorsement and braking principles: key rules to remember
Our summary of what the official handbook says on this topic, in our own words. Read it before or after the practice questions above, then check the original chapter. Read the official chapter ↗
Ch. 1 Requirements for A Endorsement (p. 1)
- An A endorsement is needed to drive a vehicle with air brakes.
- Not needed: Class 3 or 5 vehicles licensed as farm trucks, and trucks with air-over-hydraulic brakes.
- You may drive an air-brake vehicle as a learner beside someone with an A endorsement, if your licence covers that vehicle type.
- To qualify: pass the written air brake test and complete a practical demonstration, unassisted and without a checklist, on equipment you provide.
- Book through 1-844-TLK-2SGI or MySGI.
Heat, energy, traction, friction (pp. 2–3)
- The engine turns heat energy into motion; brakes turn motion back into heat through friction.
- Traction is the tire's grip on the road; the final factor that moves or stops a vehicle is traction, not the engine or brakes.
- Friction resists movement between two surfaces; brake linings pressed on drums make friction and heat.
- Drums absorb heat and pass it into the air; how much heat a drum can absorb depends on its metal thickness.
- Stopping in one tenth of the time it took to accelerate needs ten times the acceleration power.
- A poorly adjusted brake makes the other brakes do more than their share and overheat.
- Most linings work best around 120 °C, should not exceed 250 °C, and fail around 300 °C.
Speed, weight, distance and leverage (pp. 3–5)
- Brake power needed varies directly with weight and with the square of speed.
- Double the weight: double the stopping power. Double the speed: four times. Double both: eight times.
- No vehicle has enough braking power once it exceeds its limits.
- A lever multiplies force: a 4:1 lever turns 100 kg of push into 400 kg.
- psi means pounds per square inch.
- 120 psi on a 30 square inch diaphragm gives 3,600 lb. of force; through a 6-inch slack adjuster that is 21,600 inch-pounds (1,800 foot-pounds) of torque.
Stopping distance (p. 6)
- Stopping distance = reaction time + brake lag + braking distance.
- Reaction time is about 3/4 to 1 1/2 seconds; brake lag in a well-maintained air system is about 4/10 of a second.
- Braking distance depends on lining friction, drum heat dissipation and tire grip.
- Even with well-adjusted brakes a heavy vehicle will not stop as quickly as a passenger car.
Study the Air brakes: who needs the A endorsement and braking principles rules as flashcards →
Other topics
- Licence classes, endorsements and examsWhat Class 1, 2, 3 and 4 licences allow, novice-driver limits, A, G and S endorsements, learner endorsements, the knowledge papers each class writes, Class 1 MELT and commercial medical standards.
- Driver condition, speed and following distanceDistraction, fatigue, alcohol and drugs, night vision and glare, the six driving conditions, traffic tempo, the time-based following count for long vehicles, tailgaters, intersections, railway crossings and the danger zone.
- Braking, passing, parking and backingSmooth stops, downgrades and retarders, combination braking, ABS warning lights, passing and being passed, curves, gear shifting, mirrors, parking on grades, warning devices for stopped vehicles, and safe backing.
- Tires, fire safety, fuel efficiency and winter drivingTire pressure and heat, tire matching, carbon monoxide, fire prevention and extinguishers, flares, fuel-saving habits and idling, plus the essential winter checks and the six hazards of winter driving.
- Vehicle condition and trip inspectionsThe PMVI program and inspection decals, who needs a daily trip inspection, Schedules 1 to 3, minor and major defects, the trip inspection report, the circle check order, brake response tests, en route and post-trip checks, and lighting.
- Taxis, ambulances, emergency and tow vehiclesWhat Class 4 covers for hire, criminal record checks and the T restriction, emergency vehicle rules and the duties of other drivers, slowing to 60 km/h, tow truck lights and taxi driving practices.
- Vehicle weights and dimensionsLegal length, width and height limits, A, B and C trains, axle definitions, overheight and power lines, red flags, clearance and amber lights, weight systems, spring road bans, permits and weigh scales.
- Truck handling: off-tracking, turns and turn-aboutsTurning radius and off-track, positioning for curves, left and right turns with a long unit, steering a semi-trailer backward, U-turns and the highway three-point and two-point turn-abouts.
- Loads, cargo securement and bills of ladingWeight distribution on trucks and trailers, securing and covering loads, overhang flags and lights, special cargos and livestock, prohibited shipments and what a bill of lading must contain.
- Transporting dangerous goodsReporting duties, TDG training certificates, consignor, carrier and consignee responsibilities, the nine hazard classes, labels, placards and UN numbers, routes and where the shipping document goes.
- Buses and passenger safetyClass 2 buses, loading zones, bus turns and leaving the curb, passenger precautions, railway crossings with passengers, standing passengers, refusing passage and the Class 2 bus trip inspection.
- School buses and the S endorsementWho may drive a school bus, re-testing every five years, safety lights and stop arm distances, what a school bus driver must and must not do, railway crossing steps, loading and unloading students.
- Coupling, uncoupling and trainsCoupling and uncoupling a tractor-trailer with air ride suspension step by step, tug tests, landing gear, hooking up a pup-train and converter dolly, safety chains, draw-bar rules and breakaway brakes.
- Tractor-trailer operation and the Class 1 licenceWhat a Class 1 licence covers, MELT training hours, the Class 1 road and trip inspection test, fifth-wheel checks, combination braking, jackknifing, offset and alley dock backing, and heavy trailers.
- Air brake components and system operationCompressor and governor pressures, reservoirs and draining, foot valve, brake chambers, S-cam brakes and disc brakes, safety valve, check valves, gauges, relay and quick-release valves, low air warning, ratio valve and air dryer.
- Dual-circuit systems and spring brakesPrimary and secondary circuits, what happens when one fails, spring-brake chambers, parking-brake valves and the pressures at which spring brakes drag and apply, compounding, blended air, the modulator valve and caging.
- Tractor and trailer air systemsThe tractor protection system, trailer-supply valve, supply and service lines, gladhands, the hand valve, relay emergency valve, breakaways and line ruptures, bobtail valve and trailer spring brakes.
- Brake adjustment and air brake pre-trip testsWhy poor adjustment causes brake failure, push rod stroke limits, manual and automatic slack adjusters, the hammer test, service tests, steep downgrade checks, and pre-trip air tests for single and combination units.