89. You are on a steep down grade and have reached your safe speed of 40 mph. You would apply the service brakes until your speed drops to - mph.
Detailed Explanation
The correct answer is "35". This question tests controlled braking, heat management, and maintaining steering control. This is a number-based rule, so connect the value to the situation instead of memorizing the number by itself.
Correct Answer: 35
Why This Matters on the CDL Test
This question belongs in your brake safety review. Pay close attention to pressure limits, inspection steps, stopping distance, and warning signs because brake-system mistakes are a common reason CDL applicants miss endorsement questions.
How to Remember It
Say the rule in your own words, then explain why the wrong answers are unsafe or incomplete. That habit makes similar Air Brakes questions easier when the exam changes the wording.
Answer Review
Choose "35" because this answer matches the safe CDL action for brake system safety. On the knowledge test, the safest answer is usually the one that protects space, control, visibility, legal compliance, or inspection accuracy before the vehicle is put at risk.
Why the other answers are weaker
- 25"25" does not best answer this brake system safety question. When you see a similar option on the CDL permit test, compare it against the exact safety rule and choose the answer that prevents the most immediate risk.
- 30"30" does not best answer this brake system safety question. When you see a similar option on the CDL permit test, compare it against the exact safety rule and choose the answer that prevents the most immediate risk.
Test-Day Checklist
- Read the question once for the topic, then read it again for the exact CDL action being tested in Air Brakes.
- Eliminate answers that sound convenient but skip an inspection, warning sign, or safety step.
- Say the correct rule out loud before moving on so you can recognize it when the exam changes the wording.
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Start Practice TestRelated Questions
38. The proper method of braking when going down a long and/or steep grades after selecting the proper gear, is to brake until your speed is about _ miles per hour below your 'safe' speed, then release your brakes.
105. How should you check that the service brakes come on when air pressure in the system drops below a certain level?
104. How should you check that your service brakes are working properly?
17. Excessive use of the service brakes results in overheating, which can lead to:
31. Which of these is NOT a proper time to apply the parking brakes?
Keep Studying Air Brakes
Question pages help you review one rule at a time. To build test-day speed, move back into the full Air Brakes practice test and answer a mixed set without looking at the explanation first.
State CDL Practice Paths
After you understand this answer, use a state practice path to connect the federal CDL rule with the DMV test pages drivers search for most.