Do You Really Need to Replace All Four Tires?

The myth, and why it sticks around

One tire picks up a sidewall cut. You go to replace it and hear "you really should do all four." It's easy to hear that as a sales line.

Sometimes it is good advice and sometimes it isn't required. The honest answer depends on three things: what drives your wheels, how worn the other tires are, and what your vehicle maker says. Here's what the tire makers and owner's manuals actually recommend.

What the tire makers recommend

Start with the baseline. Both the U.S. Tire Manufacturers Association (USTMA) and Bridgestone recommend replacing all four tires at the same time. Bridgestone's reason is that tires are key to how a vehicle performs and handles, so the four should be as close to identical as possible. The Tire Industry Association calls it the best practice.

But none of them stop there. They also tell you how to do it when four isn't practical:

So "all four" is the recommendation, and "two, matched and on the rear" is the accepted fallback. Why the rear? That's its own question, answered in new tires on the front or the back.

Why tread depth matters more than it looks

A new tire is taller than a worn one of the same size. The difference is only the tread that's worn away, but it changes the tire's overall diameter, and with it how far the tire travels in one turn.

On a two-wheel-drive car that mostly shows up as a difference in grip between the new and the worn tires. On a vehicle that drives all four wheels, it can matter mechanically. Michelin explains that AWD and 4WD systems typically need all four tires to have the same circumference, and that even small differences can put stress on drivetrain components over time.

All-wheel drive: the owner's manual decides

This is where the "all four" advice comes from, and where it's strongest. Bridgestone says that on some all-wheel-drive vehicles, significant differences in tire diameter, as with two heavily worn tires against two new ones, may lead to excessive wear to drivetrain components. It also says matching sizes and constructions on all four is particularly important on AWD, unless the vehicle maker specifies otherwise.

The key phrase is some vehicles. AWD systems differ, and the vehicle makers set the limits. A few examples of what they say:

• Tesla's Model Y manual recommends replacing tires in pairs unless the other tires are within 2/32 in (1.5 mm) of the new tire's tread depth.
• Subaru recommends replacing tires with the same tires the vehicle came with, and if you choose a different brand, the same size and style.
• Michelin notes that some vehicle makers specify a maximum allowable circumference difference across the four tires.

We can't give you one number that covers every AWD vehicle, because there isn't one. Open the tire section of your owner's manual before you buy. If it gives a tread-depth or circumference limit, measure against it.

Two-wheel drive: pairs are usually the plan

On a front- or rear-wheel-drive car, replacing two tires is common and covered by the guidance above: matching size, load index and speed rating, same category of tire, new pair on the rear axle. Your owner's manual still has the final word, but the drivetrain concern that drives the AWD rules doesn't apply in the same way.

Measure the gap before you decide

To know where you stand, you need numbers, not a glance. Measure each tire in the inner, center and outer grooves:

Then compare:

• Across the set. How far is the most-worn tire from the least-worn?
• Against the new tire's depth. Your installer or the tire's spec sheet can tell you the new-tire tread depth.
• Against your manual's limit, if it publishes one.

Our tread depth chart shows the 2/32 and 4/32 lines in 32nds and millimeters.

Only one tire is damaged: your options

If one tire is cut, punctured beyond repair or bulging, and the other three are fairly new:

1. Check whether it can be repaired. Our repair checker walks through where a puncture can and can't be fixed.
2. If not, check the manual. On AWD, find any tread-depth or circumference limit.
3. Measure the other three. If they're close to new and within your vehicle maker's limit, a single matching tire may meet the manual's rules.
4. If they're well worn, replacing in pairs (or all four on AWD) keeps the set within the rules.
5. Follow USTMA's placement advice for a single tire: pair it with the deepest-tread tire, both on the rear axle.

How to avoid the question next time

Uneven wear is what turns one damaged tire into a four-tire bill. The Tire Industry Association notes that drivers who don't keep up with rotation often end up needing to replace one axle before the other is worn out.

• Rotate on the schedule in your owner's manual. Our rotation pattern tool shows the pattern for your drivetrain.
• Check pressure monthly, cold, against the door placard.
• Watch for uneven wear across a tire. It points to alignment or inflation.
• Keep the receipts. Knowing when each tire went on helps you judge the next decision.

The checklist

1. Read the tire section of your owner's manual, especially on AWD
2. Measure all four tires in three grooves each
3. Compare the gap with any limit your manual gives
4. Match size, load index and speed rating to the door placard
5. Choose the same category of tire as the others, ideally the same model
6. Replacing two? Put the new pair on the rear axle
7. Start a rotation schedule with the new set

Not sure where your tires stand? Run them through Do I Need Tires Yet?. If it's time, shop by size or vehicle and buy the number your manual and your measurements call for.