On Fri, 23 Jan 1998 13:11:35 +0100 Oyvind Kaurstad writes: >How can a car with ABS brakes come to a stop in a hill? It doesn't seem like it would matter whether the road is level, uphill, or downhill, just whether the tires are sliding (because the brakes locked) or not. > >Why don't the ABS-system release the brakes when the car stops? Some of the early ones did. There was an attempt to require ABS brakes on heavy trucks in the 1970's before the technology was ready. There were many failures of this sort, which caused collisions that would not have occurred with standard brakes. After that disaster, only now (after years of proving in cars) are ABS brakes being fitted to trucks again. >And now you might say that the ABS-system is deactivated below >a certain speed, which is absolutely correct=2E I think they also look for things like one wheel stopped while the others are turning, a sudden decrease in the speed of a wheel, etc. There are also a lot of self-checks to see if a sensor or other part has failed. Usually the system lights a warning light and reverts to standard brakes if trouble is detected. >But what if a car standing still starts to slide? Will the ABS-system >be able to release the brakes? Why would you want to? The best way to keep a car still would be to lock the brakes. If the tires don't have enough static friction on the road to keep the car from moving, releasing the brakes would only make it move faster.