low gearing 12-speed Ultegra Di2

[prokyon]

Hello, what are some options to low-gear Ultegra Di2? I want somethig like 30-40 as the lowest gear, so 0.75 gear ratio. On 11-speed Ultegra, I can add an Absolute Black front chainring or Rotor crankset with 30T front chainring and then use RoadLink to run an 11-40 MTB cassette in the back, giving me 30-40 as the lowest gear. Use case is bike packing in the Swiss Alps: I ran 34-40 last time and was grinding up Stelvio at 55rpm towards the end... so need to go lower on a different 12-speed bike this time.

I found this gem https://rotoramerica.com/products/12-sp ... 9049789519 which would allow running a standard compact crankset for 34-46 gear ratio as the lowest, but I'm not sure if RoadLink or GoatLink will work well with that.

[pdlpsher1]

There’s no need to spend this much. A user here mated a 10-45 with a 105 RD. It worked fine without a roadlink.


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[prokyon]

Where did you get a 10-45 12 speed cassette? The bike already comes with Di2, otherwise yeah I would just run 105.

[pdlpsher1]

Shimano XT or XTR MTB depending on your budget. I wouldn’t use any cassette without a Shimano name on it.


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[prokyon]

OK but those MTB cassettes are for MTB microspline freehub bodies - how would you fit that onto a road hub? For DTSwiss hubs, you'd essentially have to also get this, right? https://www.jensonusa.com/Dt-Swiss-Micr ... eehub-Body

[pdlpsher1]

I can't open the link you gave. Watch this video for the correct part number to get. DT Swiss makes a special MS freehub kit that is designed for their 'road' hubs, to be used for their 12-speed GRX 1x group that uses MTB cassettes. If you just buy a standard MS freehub you'll get the MTB version made for MTB hubs, not road hubs. MTB and road hubs have different dimensions.

https://www.youtube.com/watch?v=D4VUWaPv6sQ

Here's the post by Upcountry on his 10-45 and 7150 RD setup.

viewtopic.php?f=4&t=175217

[prokyon]

Thanks, sounds like for both 11 and 12 speed can just fit an XT/XTR cassette. I wonder if there's anything special about using a 105 RD instead of Ultegra (other than lower cost) and if eccentric pulley wheels are needed - it looks like he wanted to try them. I'd actually probably use a GRX RD instead as it can tension the longer chain if needed - I had too much chain bounce on my 105 11-speed system.

[Upcountry]

Hey there. Following up to my post that @pdlpsher1 posted...
I'm actually still running the setup I laid out, although I do have the parts sitting to make the move to Sram Transmission here in the next few days. I was somewhat hopeful that Shimano would release their GRX or XTR Di2 setups this year so was trying to get a little head start on that with the idea of just replacing the rear derailleur when it came out, but everything points to mid 2025. So with Sram releasing the updated Red E1 levers, I'm willing to head that direction. I previously ran a Force D2 XPLR setup on the same bike, but really disliked the ergonomics of the levers themselves, which was the main motivation for the attempts to make a 1x12 Di2 setup.

I did ride the 105 rear derailleur with stock pulleys for a few rides, and it was fine, although it took a bit of fine tuning on the B-limit screw to get the spacing off of the 45t cog just right. The offset pulley wheel made that much more forgiving. I chose this derailleur as at the time, it was the largest range di2 derailleur in their range(rated 2t larger than Ultegra or Dura Ace), as this was prior to the 2x GRX Di2 derailleur, which I would have opted for, simply to gain the clutch. You will need to swap to a Microspline freehub, but those are fairly available depending on your hub make.

One other option for cassettes is the Ingrid Components 11-44t cassette, which is available for either XD or HG freehub bodies.

[pdlpsher1]

Thanks for the update. I didn’t realize this was a 1x setup. WhenI read 105 RD I just assumed it was 2x. I guess the 10-45 wouldn’t work on a 2x as the RD cage would be too short for such a big range.


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