Grind off some teeth or not (If so how many)?

[John in CR]

With a temporary reprieve from rainy season I've been riding instead of building, but it's time to put this Nexus3 to the test. In order to still use bike chain I'm going with larger sprockets. I'm going first with the big hub motor that has pushed me past 60mph in a 20" wheel, but using it outside the wheel. My interest isn't speed, but hill climbing without strain, so I have a 36t sprocket to attach to the cover of the hub motor, and a 44t sprocket already welded to the 18t sprocket that comes with the Nexus geared hub, and the Nexus hub mounted in a 20" wheel.

As quiet as possible with chain that's turning in the 600-900rpm range is what I'm after. Something I've seen on very large chainrings is filed off every other tooth or 2 out of 3 teeth. I'm thinking of doing the same while I still have these sprockets off the bike.

How far should I go? On the front sprocket, should I grind off every other tooth or 2 out of 3, making it an 18t or 12t sprocket of large diameter. What about that rear, go make it a 22t sprocket, or grind off 3 out of 4 and make it 11t?

OR considering that it is quite likely to go unchanged unless the gearing is way off, just leave the sprockets with all teeth intact?

John

 

[spinningmagnets]

When you are using a large diameter chainring on the front bottom bracket, I believe thats when each tooth is under the most strain. However, when a small gear on a motor is driving a large chainring thats on the rear wheel, I believe the load on each tooth on the large chainring is greatly reduced.

I assume there would be some noise and friction reduction by removing teeth, but I dont know how much or if its worth the trouble. That being said, I would be very comfortable removing 1 out of 2 teeth on an aluminum chainring, and two out of three on a steel chainring. Just a thought, best of luck...

 

[John in CR]

Thanks SM,

My thought process was after seeing gaps in the teeth on extremely large chainrings on bikes apparently attempting speed records, that having fewer teeth in contact with the chain reduces friction and therefore sound too. Plus I'd like to get to odd numbers of teeth on each sprocket to promote even chain and sprocket wear, according to Sheldon Brown.

John

 

[liveforphysics]

With my GSXR1000, I have a tendency to break teeth off the rear sprocket when I use aluminum. After you loose about 5 teeth from a sprocket, it really gets noisy. I know we are dealing with less force in this situation, but I've personally only seen an increase in noise from less teeth. IMHO, dropping teeth is a bad idea, but I'm sure it would function either way.

 

[John in CR]

With my GSXR1000, I have a tendency to break teeth off the rear sprocket when I use aluminum. After you loose about 5 teeth from a sprocket, it really gets noisy. I know we are dealing with less force in this situation, but I've personally only seen an increase in noise from less teeth. IMHO, dropping teeth is a bad idea, but I'm sure it would function either way.

Thanks Luke,

That's enough evidence to save me the work. I thought of another possible reason for missing teeth on those huge chainrings...less work to make.

If noise ends up an issue, I'll just go to a belt anyway. Since I'm looking at little reduction, I think medium size pulleys can make a belt drive make sense.

John