In short. If you replace only two tyres, the tyre industry says the new pair goes on the rear axle, whether the car is front-, rear- or all-wheel drive: worn tyres on the rear lose grip first on a wet road, and a car whose rear slides (oversteer) is much harder to catch than one whose front runs wide (understeer). The only written exceptions are a carmaker's handbook that says otherwise and a staggered set-up, where each axle has its own size. On an all-wheel-drive car the first question is not front or back but whether two new tyres are allowed at all: Tesla accepts a pair only if the other tyres are within 1.5 mm of the new tread depth, Kia sets 10 mm of circumference between all four tyres, and the rest is in your handbook.
Why the new pair goes on the rear
On a dry road the difference between a new and a half-worn tyre is small. On a wet road it is not. The US Tire Manufacturers Association (USTMA) writes in its service manual that new tyres with deeper tread "will provide better grip and evacuate water more effectively, which is important as a driver approaches hydroplaning situations", and that greater traction on the rear axle on wet surfaces "is necessary to prevent a possible oversteer condition and loss of vehicle stability" (USTMA, Care and Service of Passenger and Light Truck Tires, 2017 edition, chapter 3).
Tesla's service manual explains the same mechanism in plain words: in the wet, the tyres with less tread have less traction; reduced traction at the front leads to understeer, "which most drivers are better able to react to than the oversteer" that worn rear tyres would cause (Tesla, Model Y service manual).
The tests. The most precise account we could read comes from the Tire Industry Association (TIA), which told a US National Transportation Safety Board symposium in 2014 that it had fitted two new tyres to the front axle of a front-wheel-drive car with worn tyres left on the rear, and found "significant instability" when turning or making a sudden lane change on wet pavement. Its position since then: when only two new tyres go on a front-wheel-drive car, they must go on the rear (TIA, NTSB Tire Safety Symposium 2014, slide 8). The slides do not publish speeds, tread depths or lap times. Michelin has run similar demonstrations on wet circuits, but we did not find a Michelin page that publishes the protocol, so we do not quote figures for them.
Why it feels wrong. On a front-wheel-drive car the fronts wear faster, they steer and they do most of the braking, so putting the new pair there looks logical. Michelin Australia even concedes that deeper tread at the front "can improve wet straight line braking and stopping distance", yet still puts the new pair on the rear, because a sliding rear in a wet bend is the harder situation to recover. The fronts will still be the first to be replaced next time: you move the better pair of old tyres forward, the new pair goes on the back, and the wear catches up through tyre rotation.
Who says what: front or back
| Source | Where two new tyres go | Condition or exception written by the source |
|---|---|---|
| USTMA (US makers' association) | Rear axle | Same size and construction as the tyres on the car; if the vehicle maker recommends otherwise, follow the vehicle maker |
| Tire Industry Association | Rear axle, "must" on a front-wheel-drive car | Based on its own wet tests; says the US regulator "says nothing" |
| Michelin Australia (17 July 2025) | Rear axle | Same size and type; "in the absence of a tire service professional's recommendation or consumer's preference to the contrary" |
| Michelin, The Tire Digest | Rear axle, "whether it is a front or rear, 2 or 4 wheel drive" | New or least worn tyres at the rear |
| Michelin UK | Rear axle | Front- and rear-wheel-drive cars with the same size front and rear |
| Continental UK | Rear axle ("the tyre industry recommends") | Some carmakers may recommend the front axle on front-wheel-drive cars: check the handbook |
| Tesla service manual | Rear, "must" | Pairs only, unless the other tyres are within 1.5 mm of the new tread |
Table compiled by us from the pages listed in the sources, read on 16 October 2026.
Two exceptions come out of this table. The first is a vehicle handbook that names the front axle: USTMA and Continental UK both say the carmaker's instruction then wins (Michelin Australia also leaves room for a tyre professional's advice). The second is a staggered set-up, covered below. "The fronts wear faster" is not an exception in any of these sources.
Two or four on an all-wheel-drive car?
On a car where all four wheels are driven, a new tyre is larger than a worn one, so it turns a little slower for the same distance. The drive system reads that difference as slip, or has to absorb it in its clutches and differentials. The USTMA note is direct: "For 4WD and AWD vehicles, even small differences in outside diameter may cause drive-train damage or mechanical malfunction", and some vehicle makers specifically advise against replacing fewer than four tyres.
How much difference is allowed depends on the carmaker. These are the figures we could read in a carmaker's own document:
| Carmaker document | Tolerance | What happens beyond it |
|---|---|---|
| Tesla, Model Y service manual | Other tyres within 2/32 in (1.5 mm) of the new tread depth, otherwise replace in pairs | Rotation is also due at 10,000 km or at a 1.5 mm difference; replace a tyre at 4/32 in (3 mm) |
| Kia, Pitstop PS750 (September 2023, all AWD models) | Circumference of all four tyres within 10 mm of each other | Over 10 mm, "all four (4) tires will require replacement"; a chatter in the drivetrain or failed AWD parts are the symptoms named |
| Michelin Canada, for 4WD vehicles (when the handbook gives no instruction) | Outside circumference of all four tyres within one inch of each other | Same size on all four, no radial and non-radial mix, no all-terrain with all-season |
Sources: Tesla; Kia PS750, filed with NHTSA; Michelin Canada.
Audi quattro, BMW xDrive, Subaru. Retailer pages and forums attribute tread-depth or circumference limits to these manuals. We could not read the current text in an official Audi, BMW or Subaru document, so we do not repeat those numbers. The tyre section of your handbook, or the dealer's service department, gives the figure for your model year; ask for the page, not a rule of thumb.
What 10 mm of circumference means in tread depth
This is our own arithmetic. A tyre that loses a depth d of tread loses about d from its radius, so its circumference shrinks by about 2π × d.
| Tread difference | Circumference difference (2π × d) | Against Kia's 10 mm limit |
|---|---|---|
| 1.5 mm (Tesla's tolerance) | 9.4 mm | Inside |
| 2/32 in (1.6 mm) | 10.0 mm | At the limit |
| 3 mm | 18.8 mm | Nearly twice the limit |
| 4 mm (for example 8 mm new against 4 mm worn) | 25.1 mm | Two and a half times |
| 6.4 mm (8 mm new against the 1.6 mm UK minimum) | 40.2 mm | Four times |
On a 225/45 R18 tyre (theoretical diameter 659.7 mm, circumference 2,072.5 mm), 10 mm of circumference is a 0.48 % difference in wheel speed, about 2.3 extra turns per kilometre for the smaller tyre. Two cautions apply. First, this is geometry, not a measurement: a paper by Michelin North America engineers, who measured rolling radius on a vehicle, finds that it "is not as sensitive to tread depth" as it is to the tyre's brand and model, or even its inflation pressure, and concludes that matching tread depths "is not the most relevant criteria" when replacing one tyre or a pair (SAE 2020-01-5070, 2020, abstract). Our reading is that the real change in rolling circumference is probably smaller than the table shows; the abstract gives no figure, so the table is a pessimistic guide, not a carmaker's test. Second, the same paper means a new tyre of another model can differ more than a worn one of the same model, which is why every source asks for the same size, type and pattern, and Michelin Australia for an identical product number when all four are replaced.
In practice. Measure the tread on all four tyres at several points with a gauge. If the remaining three are within your carmaker's tolerance of a new tyre, replacing one or two is allowed by that carmaker. If they are not, the carmaker's answer is four. Kia's measuring method is to raise the car until all four wheels are off the ground and run a flexible, non-metallic tape round each tyre; under a car, the car must be raised and supported on axle stands, never on the jack alone. Pressures must be equal and correct before any comparison (tyre pressure).
Staggered set-ups: each axle keeps its own size
A staggered set-up has different tyre sizes front and rear. The rear-axle rule assumes two tyres that could go on either axle; with a staggered set, they cannot. Tesla's service manual shows the consequence for rotation: with non-directional tyres of different front and rear sizes, "Move LH to RH. Do not move front to rear." A new pair simply goes on the axle whose size it carries. Kia's bulletin adds that some AWD vehicles are fitted with staggered sizes as original equipment and that the size must be read on the placard in the driver's door jamb or in the handbook. To read the size on a sidewall, see how to read a tyre size.
Our reading, which your handbook may overrule. On a staggered car with all-wheel drive, the carmaker chose the front and rear sizes so that the axles turn at the speeds its drive system expects, with tyres of similar wear. Two new tyres on one axle and half-worn ones on the other move that relationship by the circumference difference shown in the table above. Nothing we read gives a separate tolerance for that case; the Kia figure covers all four tyres. Ask the dealer before you fit a single new pair to a staggered AWD car.
One tyre only
USTMA and Michelin Australia give the same answer: replacing a single tyre can have an adverse effect on suspension systems, gear ratios, transmissions and tread wear; if it cannot be avoided, pair the new tyre with the tyre that has the deepest tread (Michelin includes a full-size spare), and USTMA puts both on the rear axle. On an all-wheel-drive car, the tolerance in the previous section decides first.
Winter tyres and mixed ratings
USTMA says winter tyres fitted to the front axle must also be fitted to the rear, on front-wheel-drive, 4WD and AWD cars alike, and that a full set of four is always preferable; fitting them only to the front "may cause the vehicle to experience adverse handling characteristics". Michelin Canada adds that if speed ratings differ, the lower speed-rated tyres go on the front axle, again to keep the rear from sliding first, and the car is then limited to the lowest speed rating. Continental UK says the same for load index and speed rating, and only when every tyre stays above the carmaker's minimum: the higher-rated pair goes on the rear. For seasonal changes in Britain, see winter tyres in the UK.
What the law says
No law we read says on which axle new tyres must go. The laws set what may be mixed on one axle, and a minimum tread depth.
| Country | Text | What it says |
|---|---|---|
| United Kingdom | Road Vehicles (Construction and Use) Regulations 1986, regulation 26 | "pneumatic tyres of different types of structure shall not be fitted to the same axle"; on a two-axle vehicle with a radial-ply tyre at the front, no diagonal-ply or bias-belted tyre on the rear axle; tyres on the driven axles, or on the steerable axles, must all be of the same type of structure |
| United Kingdom | MOT inspection manual, 5.2.3 | Tyres on the same axle of different sizes: major defect (b). Of different structure: major (c). Tread below 1.6 mm in the central three-quarters of the breadth of tread: dangerous (e). Nothing on tread difference between tyres |
| Australia | Australian Light Vehicle Standards Rules 2015 (version current at 22 November 2019), rules 48 and 52 | No pneumatic tyres of different carcass construction on the same axle (cord material and number of plies may differ); tread at least 1.5 mm deep in all principal grooves, except at the wear indicators. Check the version in force in the state or territory where the car is registered |
| United States | No federal rule on placement found | The TIA told the NTSB in 2014 that the federal regulator "says nothing" on two-tyre placement. USTMA asks for replacement at 2/32 in (1.6 mm); minimum tread depths are set by each state, which we did not read one by one |
| Canada | Provincial rules | Not read for this guide: check your province's vehicle standards; the tyre makers' advice above applies the same way |
Sources: regulation 26; MOT manual, 5.2.3; Australian Light Vehicle Standards Rules 2015; TIA, 2014. All read on 16 October 2026.
In practice, the British and Australian rules mean the two tyres on an axle must match in size (UK) and in construction (UK and Australia). Continental UK goes further and asks for the same tread pattern and brand across an axle if brands have to be mixed.
Before you buy two: five checks
- Read the handbook's tyre section for a front-axle instruction, a tread or circumference tolerance on all-wheel drive, and the sizes on each axle.
- Measure the tread on all four tyres, in several grooves, with the pressures set.
- Match the new pair to the old in size, load index, speed rating, construction and, if possible, brand and model.
- Put the new pair on the rear, unless the handbook names the front or the car is staggered; move the better old pair to the front.
- After fitting, tighten the nuts to the carmaker's torque, set the pressures to the carmaker's figures and reset the pressure monitoring system if the car has one. If the car pulls or the steering wheel shakes, have it checked before you drive on.
Frequently asked questions
Do new tyres go on the front or the back of a front-wheel-drive car?
On the back. USTMA, the TIA, Michelin and Continental UK all say the rear axle, and the TIA's own wet tests on a front-wheel-drive car with new tyres at the front found significant instability in turns and lane changes. Continental UK notes that some carmakers name the front axle on front-wheel drive: if your handbook does, follow it.
And on a rear-wheel-drive car?
Also on the back, if the tyres are the same size front and rear. If the car is staggered, each new pair goes on the axle whose size it carries.
Do I have to replace all four tyres on an all-wheel-drive car?
Only if the tyres you keep are outside your carmaker's tolerance. Tesla accepts a pair if the others are within 1.5 mm of the new tread depth; Kia accepts up to 10 mm of circumference difference between all four tyres, which is about 1.6 mm of tread by our calculation. Other carmakers set their own figure in the handbook.
What happens if the tread difference is too large on AWD?
Kia names a chatter felt in the drivetrain and the failure of drivetrain components; USTMA speaks of drive-train damage or mechanical malfunction from even small differences in outside diameter.
Can I replace just one tyre?
If the carmaker's tolerance allows it. Otherwise USTMA and Michelin say to pair the new tyre with the one that has the deepest tread, and USTMA puts both on the rear axle.
Can a tyre fitter shave a new tyre to match the others?
Some tyre shops offer to shave a new tyre down to the depth of the worn ones. We did not find a carmaker document that sets a rule for it; ask your dealer whether it meets the tolerance in your handbook.
Is it illegal to have new tyres on one axle and worn ones on the other?
Not in the UK or Australian texts we read, as long as each tyre is above the minimum tread depth and the two tyres on each axle meet the rules on size (UK) and construction (UK and Australia).
Does the rear-axle rule apply to winter tyres?
USTMA goes further for winter tyres: if they are on the front axle, they must also be on the rear, on every drive layout, and a set of four is always preferable.
Wheels from Onyx Forged
The tyres, their sizes and their tolerances come from your carmaker and your tyre fitter. Onyx Forged does not recommend a size or an offset, and does not choose between a staggered set and the same wheels on both axles; our wheel size guide and the tyre size calculator show what changes from one choice to the other. Onyx Forged is a French brand of made-to-order forged wheels, designed to JWL/VIA standards: see the catalogue.
Sources
- Tyre industry: USTMA, Care and Service of Passenger and Light Truck Tires (2017 edition); Tire Industry Association, NTSB Tire Safety Symposium 2014.
- Tyre makers: Michelin Australia, mixing new and worn tyres (17 July 2025); Michelin Canada, tires 101; Michelin, The Tire Digest, 2 tires to change; Michelin UK, tyre rotation; Continental UK, mixing tyres.
- Carmakers: Tesla, Model Y service manual, tire rotation; Kia, Pitstop PS750, filed with NHTSA (September 2023).
- Research: Kan, Hoffman and Carter, SAE Technical Paper 2020-01-5070 (2020, abstract).
- Law: Road Vehicles (Construction and Use) Regulations 1986, regulation 26; GOV.UK, MOT inspection manual, section 5.2.3; Australian Light Vehicle Standards Rules 2015 (version current at 22 November 2019).
All pages were read on 16 October 2026.
The Onyx Forged design office.