It has to do with how the tire was designed to handle the stress and load of acceleration from the drive train. When mounted in the front in the normal position, the load is from the opposite direction (front braking) that the tire was designed to handle. Mounting in reverse makes the load come from the proper direction, thus ensuring safe operation.
At least I think :dontknow:...I have a normal E111 on mine...cheers.
If you look at a Metzeler front tire, it's the exact same as a rear tire reversed. As eastcoastblur said, it has to do with "applied forces" and how the tire was designed to handle them. Some people run them with the arrow and some run them reversed. I haven't heard anyone post a negative story about running them either way, so I think it's a matter of personal preference. I've run through a flooded intersection doing about 30 mph with a reversed fat front, and the bike never lost traction or stability. I know a lot of people wonder about the tire's ability to disperse water, and I have ridden through my share showers and haven't had an incident.
The way it was explained to me is, the 160 is a rear tire and the tread and "inner crap" inside the tire are meant to propel the bike forward, as rear tires do. When you mount it in the front you need to reverse the tread so that it is more efficient as a breaking tire, as the front wheel and tire are used more for breaking.