Behold, the 929 DH. This is a frameset I am making for my senior design project at Northeastern. The thought behind the design is to utilize a single sided rear swingarm like on some high end moto gp style race bikes for quick wheel changes.

I have been toying with the idea of making an open wheel mountain bike for some time and decided that for my senior project I should pull out all the stops and try it out. I was not sure that it was feasible given the lightweight nature of mountain bikes compared to motorcycles and the increased demand for durability and strength. Once I completed the solid models and ran stress and fatigue analysis on it, I realized that it was not only viable but very functional. I went on to design a quick release style rear axle assembly which utilizes a stock front 20mm rim. The bearings and all were pressed out of the front hub so that a new low friction sleeve could be pressed in their place. The hub rides on a 30 mm axle and locks to it with pins that slide into the holes for the six bolt iso disc brake mount. The disc rotor and chainring are mounted on board the swingarm between the two 47 x 30 x 8 mm bearings. This makes it so that the wheel can be removed very swiftly while the chain and disc remain connected to the frame. 

The other reason I wanted to do the single sided swingarm is because it just looks so good. i have always salivated when I see a Ducati 1098 or a BMW that uses one because of the clean open look of the rear end. It just looks like it shouldnt be possible. But since they can do it, I dont see why I cant.

 The rest of the frame is equally intricate, from the front triangle to the suspension design, but its all done for a reason. The front triangle is neat because most all of the linkage runs through the middle of the frame. I made a double downtube and lower seat tube with the streamline tubing to connect the pivots.

The suspension is a whole other thing on its own. I came up with the particular configuration on September 29, so without being able to come up with a more appropriate name I christened it the 929 DH. Its basically another floating shock virtual pivot design like some of my others but the configuration has been tweaked around. This was done for a few key reasons. Improve the mid range travels linear feel, sharpen the progressive drop off, lower the leverage ratio overall, and lower the center of gravity of the frame as much as possible. It resembles a flattened DVP linkage in some ways. The resulting leverage curve is absolutely dialed perfectly for what I was going for. I have learned much from the design and testing of my other 3 prototypes and have distilled the design into this project. A plot of it is shown below. 

 Wheelpath was another key focus of this design. The pivots on the vp links are relatively high so that the wheel is pushed back as it is pushed up. The reason it can do this without sacrificing pedaling efficiency is the locations of the chain line. I decided to use an internal shifting hub that will be mounted 2/3rd the way up the seat tube which is at the most benefitial intersections of the ICC and CCCs.   

 Its unclear whether this would be something that could really go into production sensibly in the mountain bike world because of the inherent produce-ability shortcomings. It is a very complex design and fabricating it took about my whole spring break week. Im sure this could be done faster if I had all my machining jigs set up beforehand, but I wouldnt see it being done in any large scale. Its designed with the use of the streamline 4130 tubing in mind, because I do not trust my aluminum welding skills enough to coax me off a 20 foot drop. This aside it is a most unique design and even if no one else wanted one, I did, so I made one.