Combination_Dynamics

Question 1

What is a combination vehicle?

Answer 1

Power unit (tractor) coupled to one or more trailers

Question 2

What is off-tracking?

Answer 2

When rear wheels follow different path than front wheels in turns

Question 3

How much can a 53-foot trailer off-track?

Answer 3

Up to 5 feet or more depending on turn radius

Question 4

What causes off-tracking?

Answer 4

Rear wheels cut corner because they follow shorter path

Question 5

How do you compensate for off-tracking?

Answer 5

Turn wide and watch mirrors for trailer clearance

Question 6

What is a jackknife?

Answer 6

When trailer pushes tractor around forming V-shape

Question 7

What causes jackknifing?

Answer 7

Over-braking or loss of traction on drive wheels

Question 8

How do you prevent jackknifing?

Answer 8

Don’t over-brake and maintain traction on drive wheels

Question 9

What is trailer swing?

Answer 9

When rear of trailer swings out during turns

Question 10

What causes trailer swing?

Answer 10

Taking turns too fast or sudden steering movements

Question 11

What is rearward amplification?

Answer 11

How steering movements are amplified toward rear of combination

Question 12

Why are longer combinations more unstable?

Answer 12

Small movements at front create large movements at rear

Question 13

What is the crack-the-whip effect?

Answer 13

How sudden movements whip through multiple trailers

Question 14

How do you prevent rearward amplification problems?

Answer 14

Make steering movements gradually and smoothly

Question 15

Why are combination vehicles more prone to rollover?

Answer 15

Higher center of gravity and dynamic forces during turns

Question 16

What speeds should you use with combinations?

Answer 16

Reduce speed below posted limits especially on curves

Question 17

How much should you reduce speed on curves?

Answer 17

5-10 mph below posted speed depending on conditions

Question 18

What affects combination vehicle stability?

Answer 18

Load distribution, speed, steering input, and road conditions

Question 19

How do you load a combination vehicle safely?

Answer 19

Distribute weight evenly and keep center of gravity low

Question 20

What happens with uneven loading?

Answer 20

Vehicle becomes unstable and handling is affected

Question 21

How do you handle crosswinds with combination vehicles?

Answer 21

Reduce speed more than with single vehicles

Question 22

What makes empty trailers dangerous?

Answer 22

Less traction and more susceptible to wind and skidding

Question 23

How should you brake with combination vehicles?

Answer 23

Apply brakes gradually and evenly to prevent jackknifing

Question 24

What is the danger of sudden braking with trailers?

Answer 24

Trailer can push tractor sideways causing jackknife

Question 25

How do you handle emergency braking with combinations?

Answer 25

Apply brakes firmly but not so hard as to lock wheels

Question 26

What affects combination vehicle turning radius?

Answer 26

Vehicle length, wheelbase, and kingpin location

Question 27

How do you make right turns with long combinations?

Answer 27

Turn very wide and use mirrors to watch trailer path

Question 28

What should you watch for when turning combinations?

Answer 28

Trailer wheels tracking properly and adequate clearance

Question 29

How do backing differ with combination vehicles?

Answer 29

Much more difficult and requires constant mirror use

Question 30

What is the safest backing technique for combinations?

Answer 30

Back very slowly with spotter if available