Two or four new tires—and on which axle the new ones belong

The Short Answer

The new tires belong on the rear. Even with a front-wheel-drive car. Even if the worn ones are on the front.

That sounds wrong – steering is at the front, propulsion is at the front, and most cars have the weight at the front. Nevertheless: put them on the rear.

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Why

The reason lies in what happens when grip is lost – and the difference between the front and rear is dramatic.

The TCS describes it this way: If the front wheels lose grip, for example due to aquaplaning, the vehicle temporarily becomes uncontrollable, but maintains its direction of travel. If the loss of grip occurs at the rear, this can lead to the rear breaking out – and that is much more difficult to correct than a temporary loss of steering control.[1]

Translated:

• Front wheels slide means: The car continues straight ahead, even though you are turning the wheel. You notice it immediately, you take your foot off the gas, and grip returns. Unpleasant, but manageable – and almost everyone reacts instinctively correctly.
• Rear wheels slide means: The rear comes out. The car rotates around its own axis. The correct reaction – counter-steering, not braking – is unnatural, and those who haven't practiced it almost never do it when startled.

The rear axle is the guide axle: It keeps the car on track.[1] Therefore, the tire with more tread belongs there, regardless of which axle is driven.

That ESP catches this is only partly true. ESP can brake and distribute torque – but it cannot create grip. Where there is no grip, no electronics will help.

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The Second Reason: Aquaplaning

The first reason is driving dynamics, the second is the physics of water displacement.

A tire with a deep tread can shovel away more water. If the deeper treads are at the front and the shallower ones at the rear, the front wheels displace the water – and the rear wheels are the first to aquaplane because they have less tread available.

The result is exactly the situation described above: The rear loses grip first.

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"But the front wears out faster"

True – with a front-wheel-drive car, propulsion, steering, and weight are on the same axle. The front tires often wear out twice as fast.

This is an argument for regular rotation, not against putting the new ones on the rear. If you swap front and rear tires every 8,000 to 10,000 kilometers, you will have four tires that wear evenly and reach the end of their life at the same time. Then the question "two or four" doesn't even arise.

Practically, this is easiest during seasonal wheel changes – which is why it makes sense to note the position when storing them.

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Two or Four? The Honest Calculation

We sell tires individually and in sets, which is fine with us. What's right for you depends on three questions.

How big is the tread difference?

Under about 2 millimeters difference: two new ones are sufficient. Put them on the rear, the better old ones on the front.

Over 3 millimeters: That becomes unpleasant. Two brand new tires at the rear and two almost worn tires at the front result in a car that pushes early at the front – manageable, but unbalanced. In this case, there's a strong argument for four.

Are they the same tires?

Two new tires of a different model than the existing ones mean two different rubber compounds and two different treads on one car. Identical per axle – meaning both tires on an axle are identical – is the minimum, and that is non-negotiable.

If you can no longer buy the old ones because the model has been discontinued, you will get a mixed set anyway. Then the question is whether you want to live with that.

How old are the old ones?

Putting two new tires with two eight-year-old ones is a bad investment. The old ones will be due in two years, and then you'll be facing the same question again – with the difference that the new ones won't be new anymore. How to read the age is in the DOT article.

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What an Extra Set Costs – Specifically

For the common size 205/55 R16, the current median is around 83 CHF per tire; the middle 80 percent range from about 65 CHF to 115 CHF. Two additional tires therefore typically cost around 130 to 230 Swiss francs.

For 235/55 R19, the median is currently around 159 CHF; two additional tires there correspond to about 320 Swiss francs. Prices are a snapshot. It remains crucial whether the tread, construction, model, and age of the existing tires are technically compatible with a mixed set.

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All-Wheel Drive Has Its Own Rules

Here it becomes stricter, not for safety reasons, but because of the technology.

Many all-wheel-drive systems cannot tolerate different rolling circumferences between the axles. A tire with 8 millimeters of tread has a minimally larger circumference than one with 4 millimeters – with a rigid or viscous center differential, this means continuous slip work, which in the worst case can cost you the differential.

Some manufacturers therefore specify a maximum permissible tread difference, often around 2 millimeters. What applies to your vehicle is stated in the owner's manual. With all-wheel drive, a set of four is often not comfort, but a requirement.

We don't know your car – please check that before buying two.

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The Four Takeaways

1. The new tires belong on the rear, even with front-wheel drive. Rear-wheel sliding is more dangerous than front-wheel sliding.
2. If the tread difference is more than 3 millimeters, there's a strong argument for four new ones.
3. Always identical per axle – the same model, the same size.
4. For all-wheel drive, check the manual before buying two. A requirement may be stated there.

And the statement that makes the question superfluous: Rotate front and rear tires every 8,000 to 10,000 kilometers. Then all four will be due at the same time.

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Further Reading: Proper Tire Storage · DOT Number and Tire Age · Mounting & Appointments

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