Which Stops Quicker: 2WD or 4WD Engaged?
Think of a situation where you have two similar vehicles, like a Jeep Cherokee XJs, but one of them has 2WD engaged while the other automobile has 4WD engaged instead. As they drive across a low-traction surface, like snow, both of them hit the brakes quickly. Which would go to a screeching halt first?
In hindsight, one would think that both would be able to stop in more or less the same time. Team O’Neil Rally School crew, however, shows that it isn’t so through a demonstration. And the paint colors aren’t to blame either.
Engineer Robin Warner explained the whole process, illustrating the difference between the two. “It’s not specifically because of the 4WD that the Jeep stops faster with it engaged,” he explains. “In straight-line braking in the snow, any car will stop faster with the tires locked as opposed to rolling, (i.e., with ABS engaged).” This is because wheels that are locked transforms itself into some kind of plowing device, where instead of rolling on the surface, they’re actually digging further into it, which then creates resistance to stop the vehicle.
Warner adds, “Because these Jeeps are almost certainly built with non-adjusting proportional valves, the front-to-rear brake bias locks the fronts tires before the rears in low grip conditions. So in 2WD mode, only the front tires lock. However, because the transfer case forces all four tires to travel at the same speed, all four tires lock and slow the Jeep down faster in 4WD mode.”
He further explains, “Now, before you rip out the ABS fuse on your car, remember: Locked wheels stop faster but cannot turn at all.”
This test might work on snow and loose gravel perhaps, but it might be different on other kinds of terrain. Furthermore, different models might have varying responses. So that’s another thing to test out.
Anyway, if you find yourself in this sort of sticky situation, at least you now know that having all wheels powered helps you stop faster when you need to slam on the brakes hard.