Easier Cycling Uphill – Modifying a Campagnolo Chorus Rear Derailleur

Campagnolo Chorus Rear Derailleur with medium cage

When I go on my bike rides, for some reason, I set a goal to climb 3000 feet (914 m). With the combination of my age (67.74 years) and weight (194 lbs, 88 kg, 13.86 stone), it started to get harder for me to turn over the pedals on steep (12%-15%) grades.

I’m riding an Eddy Merckx Professional frame with 2015 Campagnolo Chorus components. I set it up with an 11 speed Campagnolo Chorus compact crank with 50/34 chainrings and an 11-29 Campagnolo Chorus cassette, which had the lowest gear at the time. The wheels are Mavic Open Pro UST rims, Campagnolo Record hubs and DT Competition Double Butted spokes.

In the 11 speed range, Campagnolo is now offering a 11-32 cassette (11–12–13–14–15–17–19–22–25–28–32). I thought that the lower gear on the new cassette would make climbing easier but the maximum sprocket size for my Chorus rear derailleur with the short cage is 29 teeth. Campagnolo has a rear derailleur technical document with the specifications. (PDF)

Campagnolo makes a medium cage for the 2015 (and later) Chorus rear derailleur (p/n RD-RE102m, see page 19 of this Campagnolo parts document), so installing the medium cage would enable me to use the 11-32 cassette.

Campagnolo 11-32 Cassette, Chorus rear derailleur medium cage, short cage

With the medium cage derailleur, 11-32 cassette and a new longer chain, I’m no longer killing myself to go up the 12%-15% grades, though the difference wasn’t as dramatic as I thought it would be. I could probably also accomplish a similar effect by losing 15 lbs.

Worn Chain

worn chain

Old SRAM PC-870 chain (top); new SRAM PC-870 chain (bottom).

The chain on my De Rosa started skipping on the lower gears on the Campagnolo 8 speed cassette. Unfortunately, by the time the chain was skipping, the lower cogs on the cassette were worn out.

Measuring from the center of one rivet to the rivet 23 away on a new chain is 12 inches (~30.48 cm). My chain was over 1/4 inch longer. Park Tool recommends replacing the chain when it is 1/16 inch too long.

Replacing the 8 speed cassette is a problem because of the dearth of parts, considering I need a ≥28 tooth lowest cog. I’ve found Miche 13-28 Campagnolo compatible cassettes on eBay in the UK and Italy, but then I start to wonder whether I should keep trying to support shifting components that were last produced in 1997.

I’ve also found on Branford Bike that a Campagnolo 9 speed hub could be used by dropping one sprocket and using a Wheels Manufacturing 8 speed spacer kit, but that spacer kit is also no longer available.

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.