The commercial driver’s license knowledge tests — adaptive practice for general knowledge, air brakes, and combination vehicles, built from the public federal manual.
Every state’s CDL knowledge tests are built from the same source: the FMCSA model commercial driver’s manual. The core battery is the general-knowledge test (inspection, control, space and speed management, hazards, hours of service) plus the endorsement-critical pair most Class A drivers need — air brakes (fail it or skip it and you carry a restriction) and combination vehicles (coupling, the lines, trailer dynamics). The tests are famously specific: governor cut-out pressures, leak-test numbers, following-distance formulas, tread depths. Most states require 80% to pass each knowledge test.
Specific numbers and procedures are what adaptive drilling is best at. Keentune’s CDL skills carry the exact figures and sequences from the public manual — with near-miss wrong answers (the adjacent PSI, the swapped step) so you learn to hold the real number, not the neighborhood — and every explanation restates the rule so it sticks. Mechanical-reasoning practice rounds out the “why” behind the systems. Original questions from the public-domain FMCSA manual — never a copy of any state’s test.
Or take a timed drill — 20 questions, 25 minutes
A focused drill on one section under a real clock — not a full practice exam, and never a predicted CDL score.
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What’s on the CDL exam
Passing score
80% on each knowledge test (typical state standard)
General knowledge
50 questions (typical)
Air brakes
25 questions (typical) — required to avoid the air-brake restriction
Combination
20 questions (typical) — required for Class A
Source
FMCSA model CDL manual (state manuals derive from it)
General knowledge
Inspection, control, space/speed management, hazards, cargo, hours of service — the universal core.
Air brakes
System components and the numbered tests — the most failed knowledge test.
Combination vehicles
Coupling procedure, the two air lines, trailer dynamics.
Counts and pass marks reflect the common state pattern derived from the FMCSA model manual; states vary. Reviewed 2026-07-17 — your state’s current manual governs.
Practice by section
General knowledge
The 7-step inspection, basic control, communication and space, speed and stopping distance, night/winter/mountain driving, railroad crossings, cargo, and hours of service.
Original practice authored from the public-domain FMCSA model CDL manual — the source every state test is built from — never actual state exam questions. States vary in details and administer their own tests; your state’s CDL manual and DMV are the authority. Keentune is independent practice, not affiliated with FMCSA or any DMV, and never guarantees a pass.
Nearly — states build their knowledge tests from the FMCSA model manual, so the material is consistent, but question counts, wording, and procedures vary at the edges. Study the material here, then skim your state’s own manual for local specifics before test day.
Which numbers should I actually memorize?
The air-brake set is the highest-value memorization on the whole CDL: governor cut-out (~125 psi) and cut-in (~100 psi), low-pressure warning (before 60 psi), spring brakes activating (20–45 psi), the leak-test limits (2/3 psi per minute single, 3/4 combination), and compressor buildup (85–100 psi in about 45 seconds). Add following distance (1 second per 10 feet under 40 mph, +1 over) and tread depths (4/32 steering, 2/32 elsewhere).
What happens if I skip the air-brakes test?
You get licensed with an air-brake restriction (L or Z) — meaning you can’t drive most real commercial equipment. Practically every Class A job requires full air-brake certification, so take it and pass it.
Does this cover endorsements like Hazmat or Tanker?
Not yet — this covers the core battery (general knowledge, air brakes, combination). Endorsement tests (Hazmat, Tanker, Doubles/Triples, Passenger) have their own manual sections; Hazmat also has a federal background check. Check your state manual for those.
All exam, test, and product names and trademarks are the property of their respective owners and are used here for identification and reference only. Keentune is independent study practice — not affiliated with, authorized, or endorsed by any of these organizations.