How to Review AWD Tire Tread Differences Before Recommending One, Two, or Four Tires

Autor: NTA    Time: 2026-10-15 09:57:19    Click:

A review procedure for service teams handling all-wheel-drive vehicles: how to compare tread depth across all four tires before recommending one, two or four replacements, with a decision matrix and a worked example.

On an all-wheel-drive vehicle, a replacement recommendation should start from a four-tire comparison: groove depths for every tire captured in the same visit, tire identity confirmed on all four positions, and inflation recorded at the vehicle maker's cold placard values. That comparison is then checked against the tire-matching and replacement requirements the vehicle maker sets for that model and configuration.

The choice between one tire, an axle pair, or a full set comes from testing each candidate fitment against those requirements, not from the condition of the damaged tire alone. No single tread-difference figure applies to every AWD vehicle, so a service lane that captures data with a tire tread depth scanner still needs the technician to apply the rule that fits the vehicle in the bay.

Illustrative tread depth dashboard; the readings shown are example values.

Why AWD Changes the Replacement Question

An AWD driveline expects all four wheels to cover nearly the same distance per revolution. Michelin's mixing guidance states that AWD and 4WD systems typically require all four tires to have the same circumference, because even small differences can stress drivetrain components over time.

Tread depth is only one input to that circumference. A 2020 SAE technical paper by Michelin North America engineers found rolling radius less sensitive to tread depth than to tire brand, model, and inflation pressure. A sound review therefore checks tire identity and pressure alongside groove depth.

Requirements are also written in different units. Michelin notes that some vehicle manufacturers specify a maximum allowable circumference variation across the four tires, while its own FAQ guideline for mixing tires on 4WD vehicles is expressed as tread depth: up to 5/32 of an inch from tire to tire. That guideline applies only when all four tires share the same size, brand, and model, their rolling radius matches, and the vehicle manufacturer does not recommend otherwise.

A Seven-Step Review Before Any AWD Tire Recommendation

1. Measure all four tires in the same visit. Readings from an earlier visit, or from the damaged tire alone, do not represent the current four-tire picture.

2. Capture every main groove on each tire. Keep the full groove profile, and note both the shallowest groove for wear screening and the value the applicable vehicle rule asks for.

3. Confirm tire identity on all four positions: size, brand, model, load and speed rating, and DOT date code. A different brand or model on one corner can change rolling radius even when tread depths look close.

4. Check inflation against the cold pressures on the vehicle placard, which can differ front to rear, and record the values used.

5. Pull the vehicle maker's tire-matching and replacement requirements for that model from the owner's manual, service information, or applicable bulletin. Record what the rule measures (tread depth, circumference, or rolling radius) and how, since a circumference limit cannot be compared directly with a tread depth spread. On vehicles built with different front and rear sizes, the maker's rule for that fitment decides which positions are compared.

6. Calculate the spreads in the measure the rule uses. For a tread-depth rule, that means within each tire (deepest groove minus shallowest groove), across each axle, and across the whole vehicle, then the same figures for each candidate fitment: one new tire, a new pair on either axle, or a full set.

7. Check the cause of uneven wear. Michelin's tread guide links one-sided wear to alignment, center or both-edge wear to over- or underinflation, and cupping to balance or suspension issues, so the matching inspection belongs in the recommendation before new tires are fitted.

Data Fields the Review Record Should Hold

A replacement recommendation on an AWD vehicle is easier to explain to the customer, and easier to audit later, when each field below is captured in the repair order or inspection record.

Deciding Between One, Two, or Four Tires

The table below is a review framework, not an automatic rule. Each recommendation assumes every tire to be fitted also meets the vehicle's original size specification, including any front-to-rear size difference the vehicle was built with.

Worked example (illustrative values)

Assume an AWD crossover with the same tire size on both axles arrives with a punctured right front tire that cannot be repaired. The vehicle maker's rule is assumed to be a tread-depth rule, and the values below are the depths that rule defines: left front 5.2 mm, left rear 5.0 mm, right rear 5.4 mm, all the same model, with a new tire of that model at 8.0 mm.

1. One new tire: 8.0 mm minus 5.0 mm gives a 3.0 mm spread, roughly 3.8/32 inch (1/32 inch is about 0.79 mm).

2. New front pair: the fronts become 8.0 mm while the rears stay at 5.0 mm and 5.4 mm, so this option leaves the same 3.0 mm tread-depth spread as the one-tire option.

3. Full set: four new tires of the same model bring the spread close to zero.

4. Compare each option with the vehicle maker's requirement in its own unit and measurement method, then record the requirement, the option chosen, and the calculated spreads on the repair order.

The numbers above are assumptions for illustration. When the vehicle maker states a figure, that figure and its measurement method set the decision line.

Explaining a two- or four-tire quote to the customer

A customer with one punctured tire may question why the quote includes two or four tires. The record built in the seven steps answers that directly: the advisor can show the four-tire readings, the maker requirement and its source, and the calculated spread for each option the shop checked.

Keeping that explanation on the repair order helps the next advisor understand the basis for the recommendation.

Where an Automated Tread Scanner Fits in the Review

Steps 1, 2, and 6 depend on capturing many groove readings across four tires in one visit. The LUBAN PRO tire tread scanner from Elscope Vision is built for passenger-car service lanes, and its product page describes automatic, non-stop scanning that can measure all grooves of each tire in one go.

For the AWD review, the scan report supplies the tread side of the record:

1. Groove-level depth for all four positions, captured as the vehicle drives through.

2. Alerts for tire wear, eccentric wear, and gnawed tires, which prompt the cause check in step 7.

3. A tire replacement alert and a wheel alignment suggestion, so alignment is discussed before new tires are fitted.

4. Customer tire inspection records with reminders for maintenance, repairs, or tire replacement, which give the next visit a baseline to compare against.

5. API docking for passing scan results into the dealership's own systems as an integration project.

A dealership can organize the handover in this order:

1. The scan runs as the vehicle drives through at intake, before the repair order is finalized.

2. The service advisor reads the four-tire report, applies the maker requirement, and prepares the candidate options.

3. The technician inspects flagged tires and wear patterns, then confirms or changes the recommendation.

4. The scan record and the advisor's calculation are attached to the customer's tire history, either through the API connection the dealership builds or by the advisor's entry on the repair order.

For step 3, the tire sidewall scanner provides tire size information and uses OCR and AI vision to identify tire brands, models, and DOT date codes. Pressure, load and speed rating checks, and the vehicle maker requirement in step 5 stay with the technician.

Bonus tips: Keeping AWD Tire Decisions Consistent Across Advisors

1. Write the vehicle maker requirement, its unit, and the candidate fitments checked into every AWD tire recommendation, so a second advisor can see why one, two, or four tires were quoted.

2. Keep the shallowest groove for wear screening and the rule-defined value for the AWD comparison as separate fields, so one number is not used for both jobs.

3. Store the full four-tire scan at every service visit, not only when a tire fails; a history of spreads shows whether one corner is wearing faster.

4. When one tire shows a large across-tread spread, schedule the alignment and pressure inspection together with the replacement decision rather than after it.

FAQ

What if the owner's manual gives no tread or circumference number?

The next references are the vehicle maker's service information and bulletins for that model. Tire maker guidance, such as Michelin's 4WD guideline, can fill gaps only where it does not conflict with a vehicle maker requirement, and the record should name which source was applied.

Can two new tires go on the front if the front pair is the one that wore out?

Michelin's guidance is to fit the new or deeper tires on the rear axle when only two are replaced, because rear traction loss in the wet is harder to recover from. On AWD, that placement must also respect the vehicle's original front and rear sizes, any directional tread, and the maker's matching requirement across all four positions.

Why record inflation pressure if the review is about tread depth?

The SAE study found that inflation pressure affects rolling radius more strongly than tread depth. Uneven pressures can therefore distort a rolling-radius comparison, which is why the record should show the pressures used.

Who makes the final call when the scan flags a tire for replacement?

The scan provides groove-level data and wear alerts across all four tires. The technician applies the vehicle maker's requirement, checks for damage that tread data cannot show, and signs off on the recommendation.

Test four-tire review on your own service lane

To see how four-tire groove data and alignment suggestions would fit your service lane and repair order workflow, contact Elscope Vision to arrange a demonstration with your team.

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