Modifying a Campagnolo Cog

Grinding the splines on a Campagnolo 10 speed compatible cog
Grinding the splines on a Campagnolo 10 speed compatible cog

After building a new wheel and acquiring a new 13-26 Campagnolo Record 8 Speed Ultra Drive cassette, I needed to change the cog in the final position from a 26 tooth to something larger so I could have a lower gear for hills. My normal ride has a Category 3 climb, according to the Tour of California’s rating of bike climbs. There is also a short 9.5% grade that I dread every time I get there, so the extra 2.6 gear-inches makes a difference.

I couldn’t find an 8 speed Campagnolo cog larger than a 26 tooth but there seemed to be Miche (Campagnolo 10 speed compatible) cogs with 27, 28 and 29 teeth for sale on eBay. According to every source I found, Campagnolo 10 speed cogs would not work on an 8 speed hub, mainly because the splines are deeper and there is a stepped-ridge on one of the splines. That’s where the Dremel cut-off wheels come in. After a few minutes with the cut-off wheel and some chamfering of the splines with a file, the 10 speed cog was now 8 speed compatible.

6 Replies to “Modifying a Campagnolo Cog”

  1. old article I know. Just thought someone could benefit from that fact that 30t aluminum 8 speed Campy cogs are available. I have two. it is the max for my 2nd gen C Record.

  2. I grew up riding the hills in Berkeley and loved it. Now I live in Austin, Texas. No hills at all! Thanks for reminding me of the joy of working on bikes and of my old rides.


  3. Followed your path to 8-speed happiness with a 10-speed 29t cog (in Huntsville, AL). The job was straightforward and easy.

    The spline shapes look so different that the idea has not even occurred to me. Also knowing that someone was able to do it left no room for hesitation!

    Thank you and best wishes,

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