The Burgtec Oval Shimano Direct Mount Thick Thin Chainring provides the mechanical advantage of increased gearing.Through research and testing of many different prototypes with varying amounts of Ovality we found 115% (from the top centre) to be the optimum.This shrank the dead spot suitably and gave the same flawless chain retention as our round rings. The shortening of the dead spot on the top and bottom of the power curve allows you to get back into the power phase of your crank rotation sooner.We would recommend sticking to the current sized round ring that you are currently using when selecting your Oval size.Burgtec Oval Shimano Direct Mount Thick Thin Chainring Highlights-Thick Thin Tooth Profile10, 11 and 12 Speed Compatible115 Degrees of OvalityFully CNC Machined from 7075 Aluminium More info