If you’ve bought a new car in the last several years, there’s an increasing likelihood that when you take a look in the trunk, you’ll no longer find a spare tire.
At best in many cases you’ll get an emergency tire inflator kit that can be used to temporarily seal a puncture and re-pressurize the tire.
On many high-performance and premium models, you won’t even get one of those if it’s equipped with run-flat tires as the 2017 BMW 530i just drove was.
While I’ve driven many cars over the past dozen years or so with run-flats, this was the first time I actually got to take advantage of capability.
Performance and fuel economy are most often thought of as mutually exclusive, but when it comes to the missing spare tire, it actually benefits both.
As wheels and tires have become increasingly large over the past two decades, finding room to package a full size spare tire or leave room to store the flat have become more problematic. That’s what initially led to the development of run-flats.
In short, these often low-profile tires are designed to be driven on for a limited distance at a limited speed even with no pressure.
According to the BMW roadside assistance rep I spoke with, the Continental tires on the 530i I was driving could go 50 miles at 50 mph. In most cases the tires have reinforced sidewalls to support the weight of the car even without air although some have a support structure around the wheel, usually some sort of hard rubber ring that takes up the weight when the tire pressure drops.
The other driver for getting rid of spares is fuel economy. The 30 to 40 pound mass of a spare tire and jack can often be enough to drop the weight of a vehicle into a lower test class for fuel economy dynamometer testing.
That can be enough to pick up an extra mpg or two on the new vehicle label. In hybrid vehicles, the battery is often installed in the space that would hold a spare, forcing the use of inflator kits or run-flats.
Read more of the original article at Forbes.