Niner's CVA Suspension

Niner's CVA suspension is covered by U.S. Patent Number 7,934,739.  Interestingly, the '739 patent is limited to 29er frames/bikes, which, according to the inventor, Steve Domahidy, require special design considerations compared to 26 inch bikes.  In particular, it was noted that the difference in bottom bracket position relative to the rear wheel dropout affects the angle of the chain that extends between the chainrings and the cogs.  The highlights of the patent "specification" are set forth below.    
 
The CVA suspension design is a dual link design in which the focus of lines passing through the upper and lower pivot points is represented by X in the Fig. 2, below, and the position of X changes through suspension compression thereby corresponding to the Constantly Varying Arc. 
 

In order to limit pedal bob, it is desirable to select pivot points that allow the chain tension to be directed near the focus of the CVA (i.e., the chain force vector passes near or through X).  Thus, it is desirable to select the pivot points so that the chain force vector intersects with X at about the rider sag amount, which typically is set at about 25% compression (as depicted in Fig. 2, above). 
"When the pivots are aligned in this manner, the chain force attempts to move the lower link down and the upper link up.  The opposing forces at least partially negate one another, thus limiting pedal bob that may otherwise result from chain tension."  Bump forces, however, urge the links in the same direction.  With this information, one can select the angles of the top and bottom linkages based on several factors, including the total amount of travel, the amount of travel corresponding to rider sag, bottom bracket height, and the desired gearing to which the suspension will be optimized.  Thus, the degree of pedal bob or resistance thereto will be affected by the rider's selection of chainring and cog.      
 
It is further disclosed that "[u]sing linkages that have equal lengths helps provide a favorable wheel path throughout suspension compression ...."  But, to obtain sufficient travel and a desired rear-axle path without an undesirably long wheelbase, in certain embodiments the bottom-front pivot is placed in front of and below the bottom bracket axle.  Another measure that may be included to keep the wheelbase in check is a forked top-rear pivot that is able to rotate past the seat tube (see 54 in Fig. 9, below). 

 

 

Additionally, it is noted that the path of the rear axle through compression has a significant impact on effectiveness of the suspension.  Referring to the Fig. 6, below, it is desirable for a rearward axle path in the initial 20% of compression, a substantially vertical path between 20-30% compression (for small bump compliance because the chain force is less likely to lock out the suspension because the chain force vector intersects or passes near to X), and a forward axle path from 30-100% (which avoids chain growth and pedal kickback).