From a press release issued by Dr. Rob Tuluie:

Tul-aris Patent Granted

One of several unique designs of the Tul-aris GP bike was recently granted a US design patent. The Tul-aris link was granted US patent no. 6581711 B1 under the title “Suspension Assembly with Compact Design and Low Center of Gravity Application.” The patent office allowed all claims without requiring any modification.

The Tul-aris link was conceived as one of the very first and integral designs of the Tul-aris has been used on the Tul-aris for over three years now. It was instrumental to the success of the project, which includes a lap record and local and national race wins. The Tul-aris link is pictured in one of several patented variations below:



Dr. Rob Tuluie, inventor of the linkage, describes its advantages as follows:
The Tul-aris link is a unique arrangement of two lever arms and pivots, which allow the shock absorber to operate in the normal fashion (compression under a bump input), while being placed underneath the engine at the same time. It connects to the lower swingarm box section on one end and to the engine case on the other, thus creating a very rigid mounting arrangement without the need for a heavy subframe or mounting braces. Not only does the Tul-aris link have low unsprung mass, it has a very low unsprung moment of inertia as well, as only one of the two links (the floating link) rotates about its center, while the other (the flexure link) is nearly stationary. In addition, the linkage positions the shock closely underneath the engine to minimize roll, yaw and pitch moments of inertia for the entire bike and places it away from exhaust heat. The compact assembly, with low overall inertias, allows the bike to turn very quickly, without the need for a radical steering geometry or ultra-short wheelbase, which can sometimes result in a lack of stability and front tire feedback. As we found during our track testing and lab simulation development work, the adjustable nature of the linkage yields kinematics such that the desired linkage ratio can be achieved with easy track-side adjustments. These adjustments allow independent changes in both first and second derivatives of shock vs. wheel travel. We found these types of adjustment to be instrumental to the performance and feel of the rear suspension. Finally, the linkage only has 4 pivots (counting all pivots, including the shock mounting points), which is one fewer than the linkages used on modern sport and racing motorcycles. The 5th joint of the linkage is a flexure joint, similar to those more recently used on Formula One car front suspensions. This type of joint reduces backlash and friction and results in a more controlled connection between damping at the shock and actual damping at the rear wheel. Lastly, the linkage was engineered using fatigue analysis software for a satisfactory fatigue life.

Another aspect of the patent is that the entire linkage assembly can, in principle, be placed into another motorcycle, with some modifications of the motorcycle required. This allows for a fundamental upgrade of the rear suspension as a whole, something that cannot be achieved by re-valving, re-springing or re-mounting of the shock alone.