2008 BMW Dirt Bike?

BMW engineers aren’t just thinking about building a full-fledge dirt bike anymore; they’ve done it. Little glimpses and photos of a new German 450 keep leaking out of Europe. And the bike is exactly what you would expect from BMW: very unconventional. Not to worry, though, the bike isn’t freakishly weird. It has the basic footprint of an off-road bike. The motor is a liquid-cooled, double-overhead-cam four-stroke. Right now it uses a Marzocchi fork and a no-link Ohlins shock, but there are reportedly other suspension designs in the works. As we would expect from virtually any all-new bike (especially one from BMW), the motor features electronic fuel injection.

Things start getting pretty interesting when you look closely at the motor. The clutch is mounted on the crank, presumably to save weight. This has been tried before, but there are usually problems associated with the much higher rotational speeds of the crankshaft. But if BMW has solved that, then there can be significant benefits in light weight and compact design.

 

In fact, the motor is very short from front the back, which allows the head and cylinder to be much less upright. That can make for less seat height, more fuel capacity, and even better cooling.

 

Another idea that has been played with in the past is a countershaft that is mounted on the same axis as the swingarm pivot. The chain will have more constant tension this way. The disadvantage, contrary to what most people might believe, is that the motor’s torque will have an even greater effect on the suspension. BMW is well aware of this phenomenon from its shaft-drive street line, and has a great deal of engineering experience in dealing with it.

 

The bike has been raced already in a number of German events and in a World Enduro Round. Joel Smets is on the development team, as well as Sascha Eckert and Simo Kirssi. Probably the most promising outing was at round two of the German Cross Country series, which was held on a military base in Walldorn. Kirssi passed almost the entire field of riders to get into  second place behind four-time World Enduro Champion Samuli Aro. An undisclosed experimental part broke, causing Kirssi to pull out, but the BMW team was still elated with the  performance. ‘We knew that this could happen as we are still trying and developing parts,’ he said later with only slight disappointment.

 

BMW still hasn’t announced a time­table for the release of the new bike, but we don’t think it will be 2008.