Modifying a Campagnolo 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.