Low Rolling Resistance
As a tire spins, the bottom flattens out to provide a larger contact patch. Bending the tread like this requires energy. A low rolling resistance tire reduces this effect by using a sidewall that is designed to flex vertically. As a side benefit, this helps the tire absorb bumps, improving the ride. Nearly all OEM tires use a low rolling resistance design to improve fuel economy. Unfortunately, it’s nearly impossible to make a tire flex vertically without also making it flex laterally, which makes the handling feel sloppy in tight turns.
Many mistakenly believe that an LRR tire won’t last as long as a traditional tire. Since only the sidewall is changed, both types of tire can use same tread compounds, which means wear and inclement weather performance remains the same.
A shorter sidewall means less lateral flex, which means better handling. Brakes are also getting bigger, which requires more space. Instead of scaling up the wheel and tire size, the total size is kept the same to decrease the overall rotational weight. Unfortunately, this also decreases vertical flex, causing a noticeable decrease in ride quality. Most handling packages go for lower profile tires, trading cornering performance for comfort.
Automakers choose to use these systems when they want to get rid of the spare tire. Performance cars that use different size wheels for the front and rear are all but guaranteed to use one of these systems, as do some high-end small cars like the Mini Cooper.
The system most drivers are familiar with is the self-supporting tire. A reinforced sidewall can support the tread and stay sealed to the wheel rim when the tire pressure drops. Typically, a tire of this design can run in this deflated state for 50 miles at speeds up to 55 mph. Once derided for their harsh ride quality, improvements in design have made these far more comfortable in the past couple years.
A self-sealing system uses a layer of sealant sandwiched within the layers of the tread. When the tire is punctured, the sealant flows out to seal the leak. This system retains the performance and ride quality of a traditional tire, although without any warning that the tire has been punctured, it’s easy to drive with a nail or rock stuck in the tread until it causes damage. A self-sealing system also doesn’t protect against sidewall punctures.
Run-flat systems can skip the tire entirely by using a reinforced ring along the diameter of the wheel. When the tire loses pressure, the tread is supported by this ring, providing performance similar to a self-supporting tire. This works on any tire installed on the rim.
What causes tread separation?
Although most people are familiar with tread separation from the Ford Explorer’s rollover lawsuit back in 2000, the problem has recently resurfaced with Goodyear recalling 41,000 Wrangler Silent Armors manufactured in 2009.
When a tire is manufactured, the casing, including the sidewall, is built as one piece. The belt and tread are glued onto this piece, and if they aren’t put together correctly, the tread will eventually peel off. Damage from impacts, wear and improperly installed tire patches can also cause tread separation.