It's great how far derailleur drivetrains have come. To compare, my vintage bike Mr Ramen has a customised 13-26 7 speed cassette and 48/32t chainrings, it had reasonably small jumps between the cassette sprockets and had a reasonably low gear of 32x26t (although I wish it was lower when I was riding in the Alps) however it was missing much of a top end which meant just coasting down most of the big hills. The thing is that there was always a penalty, you either have a good spread of gears and big jumps or a narrower spread and smaller jumps, never both without having to go to the complication of a triple crankset. I've never really liked the complexity or the poorer shifting of them. Fast forward to today and 11 speed drivetrains are still only found on higher end bikes, however they are offered by Shimano and SRAM instead of just Campagnolo.
Initially when I bought my Campagnolo Athena groupset, I had quite different intentions for it. It was attached to a lightweight skinny tyred racing bike which was mostly used for training and bunch riding quite briskly. The 50/34 crankset and the 11-25t 11 speed cassette gave very nice closely spaced gears and still had a relatively good bottom gear which was fine for climbing. However things change. Since building Phil, my all purpose Genesis Croix de Fer, I have been wanting a lower bottom gear. Partly for climbing and partly for off-road riding which is now possible on this bike.
Firstly let's look at the current gearing situation as it was. I've put together two charts comparing my gearing, units are in Gain Ratios. If you look below you can see the 11-25t cassette has no percentage changes in gear over 12% and on average they are about 9% which a still quite decently low 2.7. The closeness of the gears is quite nice, combined with the Ultra-shift shifters which allow downshifting up to 5 gears with one stroke makes it very quick and easy to find the right gear. However I was finding off-road the 2.7 bottom gear was insufficient, particularly when going through heavy mud or other obstacles. Also the 2.7 was a tad high when climbing up steeper gradients.
Before pulling the trigger I tested the gearing in my chart below. There are two 14% jumps and a 13% jump, however most of the others are quite close and the bottom gear is now a nice 2.1 which is about a 26% lower gear than previously. Also the overall gearing range is wider at 433% as opposed to the previous 337% which is significant. Being able to have this gearing range and also have relatively close ratios would have been wishful thinking only 10-20 years ago. A typical 10 speed 11-32t cassette will have 11-13-15t small sprockets which all have quite big jumps inbetween them. The 11 speed 11-32t cassette as you can see has one tooth jumps in the smallest 4 sprockets, 11-12-13-14t which is the same as the 11-25t cassette.
Now onto the installation... Firstly the challenge was being able to have sufficient chain tension with such a wide gearing range, this comes down the chain wrap. The job of the derailleur is not only to change gear but to keep sufficient tension on the chain to stop it from falling off. The derailleur needs to keep enough chain tension in the small chainring small sprocket combination but also be able to give enough chain to allow a big chainring/big sprocket combination. The way to figure this out is to do some simple maths.
Rear 11-25t cassette = 14t difference
Front 50/34t chainrings = 16t difference
However swapping to a 11-32t cassette...
Rear 11-32t cassette = 21t difference
Front 50/34t chainrings = 16t difference
The first thing to go was the short cage rear derailleur which has a rated chain capacity of 33t, and in came a medium cage Campagnolo Athena rear derailleur which has a capacity of 39t. This derailleur was originally intended to go with Campagnolo's triple cranksets however works perfectly fine on a double as well. Thanks to the flexibility of the Novatec D712SB-11 hubs, I am able to swap the freehub to a Shimano/SRAM compatible one very easily.
It's hard to say goodbye, the Campagnolo cassette is a bit of a work of art. The alloy carrier for the largest three sprockets is beautifully machined with lots of intricate cutouts and then anodised.
Now it's starting to look more like a MTB wheel...
Campagnolo specifies that the dimension between the face of the lowest tooth on the cassette and the face of the rear derailleur hanger should be 10.2-12.2mm, looks like I'm just in. This is to ensure that there is sufficient spring tension in the derailleur for changing gears. Previously the old Campagnolo cassette was a little bit under 10.2mm and I had to run a washer under the derailleur hanger bolt to space it out sufficiently enough.
There are a few other subtle differences, the backside of the derailleur hanger bolt is a Torx fitting now. Also noticeably when shifting there is a stronger spring inside the derailleur which gives more positive shifts downshifts. I was partly expecting this as I read that the original 2010 11 speed rear derailleurs were found to have insufficient spring tension which was upgraded in later models.
All done.. including my new bling super-light gold chain with cutouts and hollow pins. The shifting is actually slightly improved from before due to the slightly stronger spring in the new rear derailleur. The longer cage is also doing it's job well with good chain tension in all combinations. You'd never know it's a Shimano/Campagnolo frankenstein unless you saw the Shimano logo on the cassette lockring. However the bike does have Shimano quick releases and a front dynamo hub so really it's nothing new. Now I just have to go find some mud and some steep hills.