Sub compact (46-30, or 48-32) road bike with 9/42 cassette (or 10/42,11/42,11,40) Absolute Black,Di2

Описание: Detailed description below, of the perfect gearing I’ve found for both the uphill and the downhill here in the French Alps - for high cadence riders/mere mortals ! Most riders are unlikely to need such a huge range of gearing away from the mountains, although it would be great for touring too. It's always better to have more gears than you need, rather than less imo !

I have now completed a whole season of riding on this set up (2021), without any issues. I've even set a few fastest segment times in my age category for some popular local climbs. Shifting and pedalling is extremely smooth and quiet in all gear combinations (noisy in video as filmed in a closed room). No chain drop issues after careful adjustment.

I ride up to 200,000 vertical metres each year and have a number of top ten times on Strava for my age group on famous climbs out here , eg Col de l'Iseran (1st place). I have used a 10/42 cassette with a 50/33 crankset/chainset for the past 2 years on my Trek Emonda. I intend using the set up in this video (detail below), or similar, for some of the steeper climbs out here, eg Colle San Carlo (10km at a constant 10%) and Col de la Loze.. Knowing me, I'll probably just use it for everything though ! (Update 12/21 : I do now use it for everything !)

DESCRIPTION OF THE SET UP IN THIS VIDEO :

HUB must be Sram XD or XDR compatible. XDR (11/12 speed) replacement hubs are available for most, but not all, wheel brands.
CASSETTE is a 9/42 11 speed by E*Thirteen. It weighs 345g so more than my previous 10/42 Sram xg1195 (263g) but virtually the same as an Ultegra 11-34 cassette (339g).
CHAIN is a 12 speed Sram Eagle GX. I've been using the same model 12 speed chain on my second bike for a similar set up, as it significantly improved shifting. I think a 12 speed chain is also an advantage here to reduce chain rub against the front derailleur when in the big chainring and smallest rear sprocket (9 tooth). I haven't tried an 11 speed chain on the road yet.
CRANKSET/CHAINSET is a Shimano Dura Ace r9100 fitted with Absolute Black 46-30 chainrings, which are a straight swop with the Shimano road ones. Note that these AB rings bring the chain-line in 2,5mm compared to standard Shimano Road chainsets when fitted. This is an advantage as it reduces chain angle to the bigger sprockets. However, with my frame's downtube (oval and fattish) I had to fit a 1mm felt spacer/washer between the crank and the BB to help reduce chain rub against the front derailleur when in the small chainring. I also had to modify the front derailleur *
Note that when back-pedalling with the chain in the big chainring (46) and the biggest cog (42) the chain does drop, although not when in the small front chainring (31). This may be because of the spacer I was obliged to fit at the bottom bracket.. Importantly, this does not affect normal pedalling performance.

NOTE : I HAD TO MODIFY MY FRONT DERAILLEUR for the AB chainrings with my frame*

REAR DERAILLEUR : Di2 ULTEGRA rd-r8050GS medium cage rear derailleur (or Dura Ace r9150 if you fit a GS cage) with a Wolftooth Roadlink DM hanger extender. A hanger extender is essential with these 2 medium cage derailleur options (max official capacity w/o extender = 34). Di2 is a huge advantage as it effectively eliminates chain slack - the default setting prevents selection of the 2 smallest sprockets when in the small front chainring. Chain slack is likely to be an issue with a mechanical groupset, although I have not tried it yet..
I have refitted the derailleur return spring to the second of the 2 holes so that it is stiffer.
Note that earlier GS (medium cage) Di2 derailleurs have shorter cages/lower capacity and so a 40 cassette is probably as big as you can go.
FRONT DERAILLEUR : slightly "modified"* Ultegra r8050 Di2 front derailleur, lowered as far as possible. Bigger gap than recommended but works fine. Guess a GRX mech would allow exact spacing. Sideways adjustment not an issue with the Ultegra mech.
*NOTE : I had to modify the front derailleur by filing/grinding the forward rounded "hinge" area to allow more retraction with the AB chainrings fitted (chainline moves in 2,5mm). Until I had ground off approx 1,5mm, it was being stopped from retracting far enough by contact with the bike frame (Trek Emonda SLR 2016). To modify, I set the front derailleur in the small chainring position, marked the area to file/grind and then, once removed from the bike, I ground the rounded hinge area back approx 1,5mm. I am confident this has not compromised the strength of the derailleur and it now allows the movement necessary !

In summary:

46-9 gear combination is harder/faster to pedal than 50-10. In fact it's actually slightly harder than 56-11 !!

30-42 allows climbing 10% gradients at 9kph for a cadence of 100 (à la Froome). 30-42 is the equivalent of 34 front - 48 rear :0)

Enjoy the climbs !!