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So Where Do New Tires Go?

We dig deep try to give a final answer to a confounding and confusing tire question

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An obviously frustrated customer walks up to your service counter and explains that he went to a nearby chain tire store to have two new front tires installed on his front-wheel drive (FWD) minivan.

He was he told that the new tires had to go on the rear if there was a “significant” difference in the tread depth of the new tires compared to the old ones. He wanted to replace only the front tires because he’d experienced a lot of wheel spin during a recent snow storm.

The salesperson inspected the rear tires, estimated they had about 5/32nds of tread remaining (and would have passed a state inspection). Because of the difference in the tread depth, the salesperson said that company policy required that the new tires go on the rear. Believing they were just attempting to force him to buy four tires, he’s now at your store. Is there any reason not to put two new tires on the front of his minivan?

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Let’s start with the basics. Since most cars today are FWD and the front tires are responsible for acceleration, steering and most braking, they normally wear faster than the rears. If the tires aren’t rotated on a regular basis, they will typically wear out in pairs and the rear tires will often still have about half of their original tread depth remaining when the front tires are completely worn out.

All-wheel drive (AWD) vehicles may have more even wear rates. Rear-wheel drive (RWD) vehicles and part-time four-wheel drive (4×4) vehicles may wear the rear tires faster.

Your FWD minivan customer’s intuition is that since the front tires wore out first and there is still about half of the tread remaining on the rears, the new tires should be installed on the front axle. Because those are the drive wheels, he believes he’ll get better wet and snow traction; and by the time the front tires have worn out for the second time, the rear tires will be worn out, too.

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That same intuition is that the deeper tread of the new tires provides extra protection against a blowout. Most people believe that it’s less dangerous to have a rear tire blowout than a front because they’ll still have steering control with a rear tire blowout.

Unfortunately, intuition is wrong on both counts, and can be downright dangerous for the customer while exposing the tire dealer to significant (and expensive) liability.

Here’s why: In dry, clear weather it really doesn’t make much difference, but in wet conditions having new rubber on the rears makes a huge difference. Tiremakers and major retailers are universal and unequivocal in their recommendations that, if only two tires are being replaced, the two new tires should be installed on the rear axle.

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And that goes for FWD, RWD, AWD and even 4x4s.

Grip and Blowouts

The deeper tread of new tires will provide better wet grip and evacuate water more effectively, which delays the onset of hydroplaning. On the rear axle, this will help avoid oversteer and a loss of vehicle stability on wet surfaces. While the worn tires on the front wheels will be more susceptible to hydroplaning, drivers can correct far more easily with new tires in the back. Most drivers quickly recognize the loss of front traction and they instinctively slow down to maintain control. Rear-tire hydroplaning is much harder to correct for and is far more likely to result in oversteer, fishtailing and total loss of vehicle control.

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Blowouts are dangerous because they adversely affect a vehicle’s handling. If the blowout is in the rear, there is nothing the driver can do; there is virtually no way to control the fishtailing rear end of the car. But a driver can better counteract the effect of the blowout in front because he can maneuver the front wheels. The control is far from perfect, but it’s not the wild ride that results from a high-speed rear tire failure.

The Internet is full of videos of tests by professional and amateur drivers where sprinklers spew “rain” on the course to induce hydroplaning, which occurs when the tire cannot pass enough water through its tread to maintain effective contact with the road. The onset of hydroplaning varies with water depth, vehicle weight and speed, as well as tire size, air pressure, tread design and tread depth.

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If all other factors are equal and the front tires have significantly less tread depth than the rear tires, the front tires will begin to hydroplane and lose traction on wet roads before the rear tires. This causes the vehicle to understeer (the vehicle resists turning), but understeer is relatively easy for most drivers to control because once they sense the understeer they instinctively ease up on the accelerator, slowing the vehicle and helping maintain control.

On the other hand, if the front tires have significantly more tread depth than the rears, the rear tires will hydroplane and lose traction before the fronts. The resulting oversteer (the vehicle starts to spin out) is far more difficult to control, even for expert drivers.

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The average driver’s instinct to quickly lift off the throttle when the rear of the car starts sliding, often makes things worse because the transfer of weight off of the rear tires may make it more difficult for the driver to regain control, possibly causing a complete spinout. Even though drivers in the videos had the advantage of knowing they were going to be challenged to maintain car control, spinouts were common with new tires on the front and the worn tires on the rear.

What’s the bottom line? When tires are replaced in pairs, the new pair of tires (assuming the vehicle is equipped with the same size tires all of the way around) should always be installed on the rear axle and the existing partially worn tires moved to the front axle.

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The need to keep deeper tread tires on the rear axle to resist oversteer caused by hydroplaning is critical. Since most tiremakers recommend not rotating tires front to rear if there is more than 2/32nds difference in tread depth, this may (especially on FWD vehicles) often eliminate the possibility of ever rotating tires until a complete set of new tires is installed. The rule is the same for AWD, 4×4 and RWD vehicles: the best tires on the back.

What about winter tires? Still the same … the most tread on the back. This applies to all passenger cars and light trucks, including 4×4 and AWD vehicles. If winter tires are needed on a FWD vehicle, they must be installed on all four wheels. Here the argument for wanting the best traction on the wheels doing the pulling seems strongest. Yet, the front wheels slipping are far less dangerous than losing control of the back end.

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Beware the Lawyers

The legal community has firmly locked onto this issue. Personal injury attorney websites discuss in detail the reasons for the manufacturers’ recommendations and what to look for after hydroplaning accidents. They describe hydroplaning wrecks as often being among the most devastating on the road, and that spinal cord injuries, severe brain injuries and other disabling conditions may result.

The sites note that many tire ‘professionals’ still believe that the tires with the most tread should go on the front if it is a FWD vehicle and that the season of the year makes a difference. They point out that the customer may be asked what he prefers or the shop will simply rotate the more worn tires off the front, even when the tires are not replaced.

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They point out that the service records of the crash vehicle should be investigated.

Because all manufacturers’ recommend that the new tires should go on the back, if new tires are installed on the front the sellers or installers of such tires are clearly liable for all injuries. What should be done is so clear-cut, that the defense in these cases is often quite meek.

Recently, there have been several large settlements against installers. In a California case, the plaintiff lost control, the vehicle rolled over and the plaintiff was left a quadriplegic. While all of the tires had adequate tread, in violation of the company’s policy the defendant installed two new tires on the front. The case settled for $8.5 million. In a case against Costco and General Motors that settled for $10 million, Costco had installed two new tires on the front and a General Motors dealer had inspected the car and tires just before the accident.

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Obviously, there is a lot of risk to making a customer happy by installing two new tires on the front. The only safe policy is to simply refuse to put tires with more than 2/32nds difference in tread depth on the front axle. Some installers try to cover themselves by having the customer sign a waiver.

That might work, but you should talk to your insurance company and lawyer before you get comfortable with that policy.

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