Article

In this article, automotive engineer and tire expert, Richard Sherman addresses the often disputed topic of tire placement. This particular topic is an interesting example where industry standards and engineering logic conflict with conventional wisdom.

Tire placement and repair are frequently at issue in legal disputes when a recently serviced vehicle loses control and crashes. The experts at Robson Forensic can assist in the resolution of such disputes.

Tire Placement

An often quoted phrase, “put your best foot forward” is familiar and certainly applied by many in their personal and professional lives. In the case of automobile tires however, the opposing argument is correct; when purchasing only two new tires, manufacturers and qualified automotive engineers typically recommend placing the better tires (deepest tread) on the rear axle of the vehicle.

Though the ideal situation when replacing tires would be to replace all four at the same time, there are certain conditions that may cause a consumer to purchase only two. Goodyear, Dunlop, Michelin, BF Goodrich and other tire manufacturers recognize this scenario and specifically state in their literature to place the best tires on the rear axle of the vehicle; it is this advice that frequently defies conventional wisdom, especially involving front wheel drive vehicles.

Front Wheel Drive (FWD) vehicles have dominated U.S. auto sales since the early 1980’s. By moving the drive wheels to the front of the vehicle, underneath the weight of the engine, FWD vehicles are able to offer superior traction under acceleration, which is particularly helpful in low friction conditions (rain or snow). It seems that much of the misconception surrounding tire placement involves the fact that the front tires on FWD vehicles are tasked with steering, accelerating, and performing the majority a vehicle’s braking. It is understandable why the lay person might think it beneficial to place their best tires on the wheels that are tasked with doing so much, but they are incorrect.

Reducing the Risk and Severity of a Crash in Hydroplaning Events

The rationale for placing a vehicle’s best tires on the rear axle is based on how a vehicle behaves during a loss of traction. In a hydroplane situation, which occurs when the tire is no longer in contact with the road due to the tire’s inability to sufficiently disperse water, it is the tire(s) with the least tread that will lose traction first. When a vehicle’s front tires lose traction, the vehicle will typically understeer. When a vehicle’s rear tires lose traction, the vehicle tends to oversteer.

Oversteer is the condition in which the rear of the vehicle attempts to overtake the front in a turning or sliding event. This is commonly referred to as fish-tailing or as a car being “loose”. In understeer, a vehicle will travel closer to a straight line compared with steering input. Understeering is sometimes referred to as a vehicle “pushing”.

In the event of understeer, most drivers are able to maintain or regain control of the vehicle without crashing. In most cases, the driver’s natural reaction to ease-off the accelerator and slow the vehicle is sufficient to regain traction without incident. Oversteer situations, on the other hand, are more perilous; this type of situation is nearly impossible for the typical driver to recover from and will often result in the vehicle spinning uncontrollably or leaving the intended line of travel.

Vehicle manufacturers recognize the hazards associated with oversteer and intentionally design their automobiles to have a bias for understeer. The most common collisions involve frontal impacts and the safety equipment found in vehicles (i.e. airbags, crumple zones, etc.) is designed for this situation. In the event of a spin or slide, the sides and rear of the vehicle more frequently become the point of impact for a crash, which affords vehicle occupants less protection. The resulting injuries associated with side impacts are far more severe than those experienced in frontal collisions with similar impact forces.

The Final Word on Tire Placement

Placing the better tires on the rear of a vehicle will increase its stability. In the event of a hydroplaning event, having the better tires on the rear of the vehicle will cause the vehicle to handle in a more predictable manner.

Front tires typically wear faster than the rear tires, but that is dependent upon the vehicle and the conditions they are exposed to. Maintaining a vehicle to include proper rotation of tires, at 5000 to 7500 mile intervals, will allow them to wear more evenly. Actual wear rates between the front and rear axle can vary and intervals may need to be adjusted to compensate.

Tires are the only thing between the vehicle and the road. It is preferable to replace all four tires at the same time; however, when replacing only two tires, drivers should remember to always mount the better tires on the rear of the vehicle, maintain proper air pressure, and replace tires when, or before the tread depth reaches 2/32”.

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Industry Resources on Tires Placement

Goodyear (www.goodyear.com/email/faq/care.html)

  • When you select a pair of replacement tires in the same size and construction as those on the car, we recommend you put them on the rear axle. A single new tire should be paired on the rear axle with the tire having the most tread depth of the other three.

Michelin (www.michelinman.com/US/en/safe-driving/tire-safety/mixing-tires.html)

  • When replacing two new tires instead of four, be sure that your new tires are the same size and tire type as your current tires, and that your dealer always installs the new tires on the rear axle of your vehicle.

Tire Rack (www.tirerack.com/winter/tech/techpage.jsp?techid=52)

  • When tires are replaced in pairs […], the new tires should always be installed on the rear axle and the partially worn tires moved to the front. New tires on the rear axle help the driver more easily maintain control on wet roads since deeper treaded tires are better at resisting hydroplaning.

Tire Design & Failure Investigations

Our experts in tire design and failure analysis are frequently retained in vehicle crash incidents involving damaged or failed tires. Utilizing crash evidence and industry experience, our experts can determine if tire damage was the cause or result of a crash.

Where tire failures are found to have contributed to the cause of a crash, our engineers have the training, education, and industry experience to determine how and why tires fail. Investigations can include an examination of design and manufacturing practices. Our experts also look at the actions of tire retailers and service stations, including tire fitment, repair, and rotation.

For more information visit our Tire Failures page.

 

Featured Expert

Richard Sherman

Tire Design & Failure Analysis Expert

Richard Sherman is an automotive engineer specializing in tire design and failure analysis. He applies his expertise to the investigation of vehicle crash incidents, with a particular focus on those involving failed or damaged tires. Richard approaches his forensic casework with experience gained working in engineering positions for tire, vehicle, and automotive component manufacturers.

Prior to joining Robson Forensic, Richard worked for the Goodyear Tire & Rubber Company where he was engaged in the design, manufacture, and quality assurance of passenger vehicle tires. As a tire designer, Richard was charged with the development of new tires as well as the tuning of existing product lines to ensure consistent, reliable performance. In a later role as Quality Team Leader, Richard performed root cause failure analyses related to product quality concerns. Richard’s experience related to tire engineering and failure analysis is well complemented by the experience he gained earlier in his career selling, mounting, and repairing tires at a quick service tire shop.