About 40 percent of cars and trucks now on the road are equipped with electronic stability control, or ESC, and
each year it's seen on more and more vehicles -- especially SUVs and crossovers. The ESC systems have been very beneficial in that they reduce the propensity of these vehicles to roll-over and many new and upcoming vehicles of this type are getting them as standard equipment. The National Highway Traffic Safety Administration has even proposed making stability control mandatory on all vehicles by 2012.

However, there's a fly in the ointment. The last few years have seen the rise of the oversized wheel and tire, with the release of ever-larger rims at each auto show, it seems.. The problem is that slip control systems like ABS, TCS an ESC depend on knowing how fast each individual wheel is rotating, among other things. The systems are calibrated to each platform based on knowledge of the wheel rotational inertias, center of gravity height. The control software has adaptive mechanisms built in to compensate for varying wheel sizes, but they can only go so far and when buyers put some exceptionally large wheels on, the systems just can't work right. If things get too far out of range, the system can either modify the vehicle behavior in unexpected ways, or cause a fault to be detected even when there's nothing wrong with the system itself.

The Specialty Equipment Market Association (SEMA) is worried that mandating ESC will not include a requirement that the systems work with aftermarket parts. However, this is totally unrealistic. The engineers who develop these systems test them with all kinds of combinations of over-sized and under-sized tires, but they can't possibly check every combination or even guarantee what will be put on the vehicle down the road. Nobody knows what kind of tires or what sized wheels will come out two, three, eight years down the road. If anyone should be required to ensure compatibility, it should be the aftermarket companies. The stability control systems are sold in good faith based on known hardware. If someone changes that hardware beyond certain limits, they should be responsible for the consequences. The Detroit News has an article about problem.

[Source: Detroit News]

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