Truck tire tread depth in Canada: the limits in millimetres, axle by axle

Five rules, one tire: which limit applies when

A Canadian truck tire is judged against several standards, and they do not use the same number. The National Safety Code (NSC), published by the Canadian Council of Motor Transport Administrators and adopted or mirrored by every province and territory, supplies three of them. Provincial law and the roadside criteria of the Commercial Vehicle Safety Alliance (CVSA) supply the rest.

• NSC Standard 11, Part A, the maintenance standard your shop works to between inspections.
• NSC Standard 11, Part B, the periodic motor vehicle inspection (CVIP, or the annual inspection in Ontario): a tire below its limit means no decal.
• NSC Standard 13, Schedule 1, the driver’s daily trip inspection.
• Provincial rules, such as Ontario’s tire regulation under the Highway Traffic Act and Quebec’s safety standards for road vehicles.
• The CVSA out-of-service criteria, which inspectors in Canada, the United States and Mexico apply at the roadside.

Standard 11 explains how its own conditions relate to the roadside ones: the CVSA out-of-service criteria are similar to, but not identical to, the hazardous conditions in the standard, because the criteria apply at a roadside inspection and the hazardous conditions in a shop. On the steer axle the roadside line is the lowest and the periodic inspection line is well above it, so a tire that will not get the truck parked can still cost you a decal.

NSC Standard 11: the shop limits and the inspection reject criteria

Part A: what the maintenance program must hold

Section 9 of the maintenance standard, tires and wheels, sets a floor of 3 mm on front tires and 2 mm on rear tires, and warns that a vehicle hauling dangerous goods may need a different minimum under provincial law. The same section rules out:

• a retreaded tire on an active steering axle, retread material that is loose or separating from the casing, and regrooving on any tire not marked “Regroovable”;
• a cut or crack longer than 25 mm that goes deeper than a major tread groove or into the casing ply, exposed body cord, or a missing piece of tread longer than 25 mm;
• a bump or bulge showing tread separation, a plug-type repair in a sidewall, UV damage more than 3 mm deep, and a tire that touches any part of the vehicle;
• radial and non-radial tires mixed on one axle, a rim that does not match the tire size, and a tire labelled “Not for Highway Use” on a public road;
• pressure more than 10% above or below the recommended figure, more than 10% difference between duals, a leak, or a damaged valve stem or missing cap.

Part B: what fails the periodic inspection

At the periodic inspection the technician finds the spot on each tire where the tread is lowest, measures it in a major tread groove with a gauge, and never on a wear bar. The standard defines a major tread groove as one of the deepest moulded grooves running around the tire through the full thickness of the tread rubber, the kind that holds the wear bars. The lowest measurement goes on the inspection report, and when a tire is replaced after a failed inspection, the readings of both the old and the new tire are recorded.

The vehicle is rejected when a tire on an active steering axle has less than 3 mm or any other tire less than 2 mm. Below 2 mm on a front tire or 1 mm on a rear tire is a hazardous condition: repairs are needed before the truck goes back on the road. The standard also notes that some jurisdictions require at least 3 mm on every tire of certain vehicles. Other reject criteria worth knowing for the shop: tires on one axle whose nominal size differs by more than 25 mm, duals whose diameters differ by more than 13 mm, and pressure more than 10% above or below the recommendation, which the inspector measures and records before and after any correction. A bulge of up to 9 mm from a sidewall repair is acceptable.

An active steering axle is one the steering wheel controls directly; a passive steering axle turns in response to lateral force. Our CVIP and periodic inspection guide covers how often each province inspects.

Ontario and Quebec set their own numbers

Ontario: Regulation 625 and the daily inspection

Ontario’s Tire Standards and Specifications regulation (R.R.O. 1990, Reg. 625) sets the provincial wear limit. A tire may not be worn so far that, in any two adjacent major grooves at three equally spaced points around its circumference, the tread wear indicators touch the road or less than 1.5 mm of tread remains. A front tire on a motor vehicle with a gross vehicle weight rating over 4,500 kg needs at least 3 mm, measured the same way. Siping does not count as tread, and on a tire with no major grooves the depth is read where the tire maker designates.

The same regulation bars regrooving or recutting a tire not designed and marked for it, duals that touch or whose diameters differ by more than 13 mm (or circumferences by more than 41 mm), and tires marked “not for highway use”, “farm use only” or “competition circuit use only”, or carrying the letters SL, NHS or TG after the size. On the front of a bus, a tire may not carry added tread material.

Ontario’s daily inspection schedules in Regulation 199/07 list “tire tread depth is less than wear limit” as a major defect, and a footnote points to section 3 of Regulation 625 for that limit. The MTO truck handbook repeats the 1.5 mm and 3 mm figures, asks drivers to check tires and wheels on the pre-trip inspection, and advises re-checking wheel fasteners between 80 km and 160 km after new tires or wheels go on, with the work done by a certified tire installer or a mechanic.

Quebec: the SAAQ mechanical inspection guide

The SAAQ’s Road Vehicle Mechanical Inspection Guide (updated August 2024) is based on the Highway Safety Code and the Regulation respecting safety standards for road vehicles. For vehicles with a gross vehicle weight rating of 4,500 kg or more, it lists as a minor defect a steering-axle tire with less than 3.2 mm (4/32 in) in a groove and any other tire with less than 1.6 mm (2/32 in). It lists as a major defect two adjacent grooves under 1.6 mm on a tire on the active steering axle of a motor vehicle, or under 0.8 mm (1/32 in) on other single or dual tires. The guide treats 1.6 mm as the height of a tread wear indicator and asks the mechanic to measure in a main groove, never at the wear indicator or a stone ejector, and to write the measurement on the report.

A minor defect gives the owner 48 hours to make the repair; a vehicle with a major defect stays off the road until the repair is proven. Quebec’s mandatory maintenance every six months also comes with a brake and tire measurement record (Registre de mesures de freins et de pneus); brake readings are required on vehicles rated 7,258 kg or more, and tire readings on it are optional. Fleets that fill them in anyway already have a tread log.

The trip inspection and the roadside

Schedule 1 of NSC Standard 13, the trip inspection for trucks, tractors and trailers, splits tire problems in two. Damaged tread or sidewall and a leak are defects, recorded and reported to the carrier before the next inspection; a leak that can be felt or heard counts as a flat. The major defects are a flat tire, tread depth below the wear limit, a tire touching another tire or any part of the vehicle other than the mud flap, a tire marked “Not for highway use”, and cords showing in the tread or outer sidewall. A truck with a major defect may not be driven until it is fixed.

At the roadside, a CVSA inspection bulletin quotes the out-of-service criterion for tires on the front steering axle of a power unit: less than 2/32 inch (1.6 mm) in any two adjacent major tread grooves, usually the ones that contain a wear indicator, at any point on the tire, never measured on a stone ejector or wear indicator. CVSA updates its criteria every year; the full tire section is in the current edition.

Compare that with the inspection line. A steer tire reading 2.5 mm will not be put out of service at a roadside inspection, but it is under the 3 mm NSC reject line, under Ontario’s 3 mm front-tire minimum, and a defect under Quebec’s 3.2 mm. Plan steer replacements around the inspection numbers, not the roadside one.

Tires were CVSA’s vehicle focus in the 2025 International Roadcheck. Across North America they made up 21.4% of vehicle out-of-service violations, second only to brakes; in Canada the share was 9.5%.

Measuring in millimetres

Every Canadian rule above is written in millimetres, while many gauges and older shop habits run in 32nds of an inch. Most gauges show both scales, and CVSA’s bulletin tells inspectors to check which one they are reading. One thirty-second of an inch is about 0.8 mm, so the common readings convert like this:

The table explains a common surprise: a drive or trailer tire at 2/32 inch meets Ontario’s regulation but fails the NSC periodic inspection, so it will cost a decal at the next CVIP. The habit to build is to read and record in millimetres.

The method is the same whichever rule you check against. Put the gauge in the centre of a main circumferential groove, never on a wear bar, stone ejector or other raised part of the tread, and press it down on its base. Before you start, confirm the probe fits the groove and the gauge reads zero against a flat surface; afterwards, lift it out by the barrel without touching the probe. Repeat across every main groove, then at two more points spaced around the tire, as Ontario’s three-interval rule requires, and record the lowest figure, as Standard 11 does. Newer tires with hidden grooves that open as they wear are full depth from new and can be read with an ordinary gauge; CVSA notes that North America sets a minimum depth but no minimum groove width.

A tread log that pulls tires on time

One reading tells you whether a tire is legal today. A series of readings tells you when it will stop being legal, which is what you need to order tires and book the truck. Keep the log by unit and wheel position, in millimetres, with the odometer in kilometres:

• When: at each PM service, each tire mount and removal, before each periodic inspection, and after any roadside tire violation. Drivers still look at every tire on the daily trip inspection.
• What: unit, position, date, odometer, the lowest reading, and the tire’s brand, size and serial so you can follow it when it moves.
• Pull point: your own replacement depth for each position, set a few millimetres above the legal line so no tire crosses it between two readings.
• Why it came off: worn out, damaged, irregular wear or sent to the retreader. Over a year this tells you where tires are being lost.

The same log gives you tire cost per kilometre: add everything a tire cost (purchase, mounting, repairs, retreads), take the distance between its first mount and final removal from the odometer, and divide. A drive tire and its one retread that cost 760.00 together and ran 352,000 km come to about 0.0022 per kilometre, in your own currency. Compare brands, retreaders and positions on that figure rather than on purchase price.

Retreads and regrooved tires in Canada

Canada is stricter than the United States on the steer axle. NSC Standard 11 rejects a retreaded tire on any active steering axle, in maintenance and at the periodic inspection; retreads are allowed on a bus tag axle, whether it steers actively or passively. Retread material that is loose, missing or separating from the casing fails the inspection, and a separation wider than half the tread is a hazardous condition. Regrooving is allowed only on a tire marked “Regroovable”, and Ontario’s regulation says the same in its own words.

Quebec’s guide lists a recapped tire on the front steering axle of a vehicle rated 4,500 kg or more as a defect unless the vehicle has two active steering axles, and a recapped tread separating from its casing by more than 6 mm. Ontario bars added tread material on the front tires of a bus.

Trucks bought from American fleets deserve a look before their first Canadian inspection. US rules (49 CFR 393.75) bar retreads on the front wheels of buses and regrooved front tires above a load rating on trucks, but not retreaded front tires on trucks, so a retread on the steer axle can arrive legally on a US unit and must come off here. The American limits are in our US tread depth guide. Simplest policy: new tires on every steering axle, retreads on drive and trailer positions.

Winter: chains, studs and winter tires

None of the heavy-truck rules quoted here sets a separate winter tread depth, so the year-round limits apply in January too. The seasonal rules are about traction devices:

• British Columbia: drivers must obey winter tire and chain signs from October 1 to April 30 (to March 31 on some highways away from mountain passes and high-snowfall areas). Commercial vehicles with a licensed gross vehicle weight of 11,794 kg or more must carry steel link chains. Trucks from 5,000 kg to 11,794 kg carry chains or acceptable traction devices unless they run winter-rated tires with the three-peaked mountain and snowflake symbol or the M+S symbol.
• Quebec: the December 1 to March 15 winter tire requirement covers vehicles registered in Quebec except heavy vehicles, tool vehicles and farm machinery. Studded tires are allowed from October 15 to May 1, but only on passenger vehicles, taxis and commercial vehicles up to 3,000 kg.
• Ontario: Regulation 625 allows studded tires only from September 1 to May 31, mainly for permit holders in Northern Ontario, and on a vehicle over 3,500 kg only if it is an ambulance, police or fire vehicle, school bus, public utility emergency vehicle or road service vehicle.

Snow and slush are when worn drive tires hurt most, so the start of winter is a sensible moment to read every drive position and move your pull point up if the log shows tires close to it.