The Absolute Black Road Oval Dura Ace R9100/Ultegra R8000 Chainrings are designed for a new type of Shimano cranks: Dura-Ace 9100 & Ultegra 8000 only. These are the finest oval chainrings from Absolute Black in terms of shifting, smoothness of pedaling and manufacturing quality. They can also be retrofitted to 9000 and 6800 cranks. 10/11/12 Speed compatible. Absolute Black Road Oval Dura Ace R9100/Ultegra R8000 Chainring Features/Advantages One of a kind special oval shape that helps you climb easier and faster (Patent Pending) Over 15% stiffer than Rotor Q-Rings due to thicker, 5mm construction Bespoke Absolute Black 6 point ramp and recess shifting design shifts better than any other brand and model of oval chainring Finest design that provides excellent strength to weight ratio You will not feel the oval shape while pedaling Your pedaling action will feel smoother Helps reduce stress on knees and helping your legs remain fresher for longer You will be able to maintain better cadence while climbing Reduces possibility of leg cramps You will reduce chainring/cog shifts by at least 15% Absolute Black Road Oval Dura Ace R9100/Ultegra R8000 Chainring Weights 34T (31g) 36T (37g) 38T (41g) 39T (42g) 50T (120g) 52T (137g) 53T (139g) Absolute Black Road Oval Dura Ace R9100/Ultegra R8000 Chainring Specifications Compatibility: Shimano Dura-Ace 9100, R9150 Di2 and Ultegra 8000, R8050 Di2. They can also retrofit 9000 and 6800 cranks but use bolt covers for best appearance. 10 / 11 / 12spd compatible. Materials: CNC machined 7075 Txxx Aluminum. Long-lasting construction. Type II anodizing. Mounting: 110 BCD x 4 Ovality: Optimized to each size separately. 34T- 6.5% ; 36T, 38T, 39T- 11.4%, 50/52/53T - 10-11.2% ; Timing of 108 -110.5° after TDC (top dead center) - Ideal for road climbing. Patent Pending. IMPORTANT: Ramps on big rings are specially configured for combinations: 50/34, 52/36, 52/38, 53/39T. If you wish to use other configurations it will also work, but shifting will be slower and may require more adjustments of the front derailleur to be acceptable. Also, remember that the front derailleur can only accept a max 16T difference between 2 chainrings - this is how Shimano and Sram designed them.