Breakdown Was Yesterday

2023 Author: Eric Donovan | [email protected]. Last modified: 2023-08-25 09:36

For many drivers, a flat tire is a drama. But that need not be. Run-flat tires save you having to change a flat tire.

Changing tires at the roadside is a thing of the past with run-flat tires. Even with a complete loss of air, you can still drive to the next workshop. Almost every manufacturer now has corresponding tires in their range.

Two different versions of run-flat tires determine the market. With the Pax system developed by Michelin, a rubber ring attached to the rim bears the weight of the vehicle in the event of a breakdown. The technology has been on the market for a few years, but could not establish itself because special rims are required. Other manufacturers instead rely on tires with reinforced sidewalls that support the car and can be combined with all rims. Even Michelin now also offers this variant. Since a loss of pressure is hardly noticeable while driving, an electronic pressure control system is required when using run-flat tires. Via the option list, it costs from 200 euros, depending on the car model, retrofit kits are available at similar prices.

More space in the trunk

In addition to puncture protection, there are other advantages. Since the spare wheel can be dispensed with, the space in the trunk increases. In addition, the vehicle weight is reduced by around 25 kilograms, which is reflected in fuel consumption.

In addition to these advantages, the tires, which are often called “run-on-flat” or “run-flat”, also have disadvantages. Above all, driving comfort suffers. Since the side walls of run-flat tires have to bear the entire weight of the vehicle in the event of air loss, they must be particularly strong and stiff. This is already at the expense of the suspension with the correct air pressure. Especially at low speeds, run-flat tires offer significantly less rolling and noise comfort than conventional tires.

Special shock absorbers

The technology has evolved over the past few years, so that the tires have become significantly more supple; however, it is not yet enough for comprehensive acceptance. This is why vehicle manufacturers and chassis specialists are now also working on this problem. Supplier ZF Sachs, for example, offers shock absorbers specially tailored to run flat tires, which are now celebrating their premiere in the new model year of the BMW 3 Series.

A special feature is that the damper reacts differently in the rebound and compression stages. Thanks to a special linear valve in the piston, the wheel rebounds particularly evenly, which ensures a high level of ride comfort. During compression, as usual, the force increases with increasing spring travel, which ensures safe and agile driving behavior.

It should be noted, however, that run-flat tires cannot completely replace the spare wheel. After driving around 100 kilometers at medium speed, they too give up and a tire change is due. This can be a problem, especially on public holidays or abroad if the right size and brand cannot be found. Those who have a suitable spare wheel with them do not have these problems. (mid)