02-17-2016, 02:32 AM
The link I shared was to a formula SAE team. They use a motorcycle engine in a small racecar. With an aero package creating down force and sticky racing tires, that is where you would start to see failures because the sprockets are loaded higher than on a motorcycle. It is also an engineering design competition, so it is important to go through the small details of every part of the car design.
On a bike, I would need to know more to know the limiting factors and actual loads. But, most factory sprockets wear out at the teeth first and they are likely designed that way intentionally for the intended applications. Most of that wear is from dirt and grime getting in between the mating surfaces.
In an aftermarket sprocket, you can cut material out of the center safely up to a critical point. The load will redistribute to the remaining material. The more material you remove means higher load and greater deflection (bending, twisting, stretching) on the smaller cross section that remains. All metals have an elastic region where all of that deflection can be recovered once the load returns to zero. As long as you don't exceed that linear limit, the material will go back to its original shape.
Then there is fatigue, bend a paper clip back and forth until it breaks and you have experienced a fatigue failure. The reduced sections on a sprocket will bend more than a sprocket without a cutout. They will then fail from fatigue faster than a sprocket without cutouts.
I cannot tell you if a sprocket will fail first from normal wear at the teeth or catastrophic fatigue in the reduced section without first knowing the geometry, material, and load parameters. I can only tell you I am concerned enough to say it is worth checking if you design a new sprocket.
On a bike, I would need to know more to know the limiting factors and actual loads. But, most factory sprockets wear out at the teeth first and they are likely designed that way intentionally for the intended applications. Most of that wear is from dirt and grime getting in between the mating surfaces.
In an aftermarket sprocket, you can cut material out of the center safely up to a critical point. The load will redistribute to the remaining material. The more material you remove means higher load and greater deflection (bending, twisting, stretching) on the smaller cross section that remains. All metals have an elastic region where all of that deflection can be recovered once the load returns to zero. As long as you don't exceed that linear limit, the material will go back to its original shape.
Then there is fatigue, bend a paper clip back and forth until it breaks and you have experienced a fatigue failure. The reduced sections on a sprocket will bend more than a sprocket without a cutout. They will then fail from fatigue faster than a sprocket without cutouts.
I cannot tell you if a sprocket will fail first from normal wear at the teeth or catastrophic fatigue in the reduced section without first knowing the geometry, material, and load parameters. I can only tell you I am concerned enough to say it is worth checking if you design a new sprocket.