Its not just that the rear tires have to slip before the front engages, it is more the fact that the rear tires need to continue to slip for the front to stay engaged. So your rear tires are turning 20% faster than your front tires with the old system. They only need to turn 4% faster with the new system. Where this makes a difference is in snow, and on very narrow shelf trails with a big drop off right beside the trail. You don't want the rear tires to need to spin for the front tires to pull, because the rear tires spinning will tend to make the rear of the machine walk to the downhill side, and off the side of the trail.