Keentune is a private study app, not affiliated with, endorsed by, or acting for the FMCSA, any state DMV, or any government agency. It cannot issue a permit or license, schedule a test, or process an application; for those, use your state’s official DMV website.
CDL · General Knowledge
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What is the minimum tread depth for a truck’s front (steering) tires?
The commercial driver’s license knowledge tests — adaptive practice for general knowledge, air brakes, and combination vehicles, built on the federal regulations.
When’s your CDL?
You’ll get a countdown and a daily pace — a study signal, never a pass guarantee.
Or pick the exact date
Every state sets its CDL knowledge tests on top of the same federal floor: the commercial driver rules in 49 CFR, issued by the Federal Motor Carrier Safety Administration (FMCSA). 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: air pressures, warning thresholds, tread depths, hours-of-service limits. 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 from the federal regulations — 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. Every question is original, written in Keentune’s own words from the federal regulations — never copied from the AAMVA model CDL manual, a state CDL manual, or 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. Drills are free.
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
Federal CDL regulations, 49 CFR Parts 383, 392, 393, 395 and 396
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; states vary and set their own tests. Reviewed 2026-10-04 — your state’s current CDL manual and licensing agency govern.
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.
Keentune is not the DMV and not a government website. It is a private study app, not affiliated with, endorsed by, or acting for the FMCSA, any state DMV, or any government agency, and it cannot issue a permit or license, schedule a test, or process any application. Practice here is original, written from the federal CDL regulations in 49 CFR (a US government work) — never copied from the AAMVA model CDL manual, any state CDL manual, or actual state exam questions, and not affiliated with AAMVA. States vary in details and administer their own tests; your state’s CDL manual and DMV are the authority. No pass is guaranteed. FMCSA is a US government agency; its name is used here for identification only.
Nearly — every state tests the same federal requirements, 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?
Start with the numbers the federal rules fix. The low-air warning must come on at 55 psi or half the governor cut-out pressure, whichever is less (49 CFR 393.51). The tractor protection valve must close automatically between 20 and 45 psi, and a trailer that breaks away must brake itself (393.43). Front tires need 4/32 inch of tread, the rest 2/32 (393.75). A property-carrying driver may drive 11 hours, inside a 14-hour window, after 10 hours off (395.3). Your state manual adds procedure numbers on top; learn those from it directly.
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.