Saturday, July 6, 2013

Don't buy aluminum sprockets

If you or someone you know is planning on partaking in the phenomenon known as aluminum sprockets, please consider the following:

Here is a steel 50 tooth sprocket that I used for at least 4 years.  I used this sprocket almost exclusively and would only shift the back gears.  Notice the lack of wear.  I replaced it because I was having drive train problems across the board and I thought it was part of the problem, also some of the teeth were chipped off on the end.
Steel sprocket
Here is the tiny sprocket from the same configuration.  This was seldom used and therefore the teeth on it are almost immaculate.
Aluminum Sprocket
This is the aluminum sprocket I purchased to replace the middle sprocket.  This one was used for only a year and 3 months.  However, once my shifters failed again, I set up my bike to use this sprocket only and the 14 tooth one in the back.  I used it like that heavily for the last 6 months, around 100 miles/ week.
Aluminum Sprocket wear
Now rotating the same sprocket 90 degrees, perpendicular to the crank arms, this shows the real wear.  Since most of the force was applied when the crank is being pushed down, this part was worn the worst.  Now, when the teeth are so worn that they are pointy, that is not a good thing, I should've noticed this earlier.  Also this sprocket stretched my chain by almost 1/4" per foot.  The previous chain running on the steel setup was only half as bad when it fell off, after more than 4 years of use. 
More aluminum sprocket wear
Another thing that bothers me, these sprockets are CNC machined.  Sure it's great to buy things made in the USA, but naturally you expect them to be better.  I don't see any advantage of machining a sprocket.  It seems like a punch pressed item, which would be much faster and less expensive.

None of the other aluminum bike components like cranks, pedals, rims, hubs, brakes, brake levers, stems, or handlebars are constantly exposed to wear by a steel object.  It seems like folly to make sprockets out of it.  Leave them for the racers and their sissy bikes that break with minor damage.

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