Shimano 2x12 with 46-30 front and 10-45 Rear?

13 replies · 1,285 views

John Z
174 posts
#1Jun 10, 2024, 9:54 AM
I have always found 46x11 lacking for fast descents. Now that Shimano offers 12-speed gruppos with a 10, my dream has come thru, except of course that the GRX cassette is a 10-36. Much of my gravel riding includes prolonged grades of greater than 10%, and since I am not a masher, I would like to have at least a 40. So, I am back to a nonstandard solution. My current driveline has road front shifters, 46-30 chainrings, and 11-40 rear XT cassette.

Now, Shimano offers a 10-45 rear XT cassette. In theory, I would need the following:

RD-M8120-SGS 10-45 SHIMANO DEORE XT Rear Derailleur 2x12-speed $77
CS-M8100-12 SHIMANO DEORE XT 12-Speed MTB Cassette Sprocket $165
FD-R7100-F SHIMANO 105 Front Derailleur (Brazed-On Mount) 2x12-speed $47
ST-R7120-L SHIMANO 105 Hydraulic Disc Brake DUAL CONTROL LEVER 2x12-speed $355
ST-R7120-R SHIMANO 105 Hydraulic Disc Brake DUAL CONTROL LEVER 2x12-speed $355
WP-Y0SS9801T Chainring 30T for FC-RX610-2 $28
WP-Y0SS98010 Chainring 46T for FC-RX610-2 $45
CN-M8100 SHIMANO DEORE XT 12-Speed MTB Chain 138 Link $48

Total: $1120.

However, there is the rear hub compatibility issue, so I would also get a new rear wheel:

Shimano GRX WH-RX880-700C Wheel Rear Carbon $850.

That brings the cost to $1970, plus labor as I will be paying my LBS to perform the conversion.

I see two issues:

1) Is the 138 link chain long enough?
2) This is the main issue, Wolftooth does not yet offer a 12-speed Tanpan.

Thoughts?
0
stu
646 posts
#2Jun 11, 2024, 1:00 PM
That's a bag of money!

Personally I would consider the following:
1) A crankset with more chainring choices.
2) A larger big cog for your 11-sp cassette.
3) Separate brake and shift levers. In your price list over $700 for levers stands out.

Fortunately I have more modest requirements so I've been fine using all three of the above.
0
3TX
55 posts
#3Jun 11, 2024, 9:01 PM
Could you just change to the GRX 48/31 cranks/chainrings for some more top end speed with the 11-40 or 11-46 cassette? ...I haven’t tried it, but there’s a post on Reddit: "I'm currently running 48/31 with 11-46 11 speed. I have the 1x deraileur with the m8000 sgs deraileur cage plates. Shifts flawlessly."
https://www.reddit.com/r/gravelcycling/comments/17u7bss/new_shimano_grx_2x12_cassette_options/
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John Z
174 posts
#4Jun 11, 2024, 10:16 PM
Could you just change to the GRX 48/31 cranks/chainrings for some more top end speed with the 11-40 or 11-46 cassette? ...I haven’t tried it, but there’s a post on Reddit: "I'm currently running 48/31 with 11-46 11 speed. I have the 1x deraileur with the m8000 sgs deraileur cage plates. Shifts flawlessly."
https://www.reddit.com/r/gravelcycling/comments/17u7bss/new_shimano_grx_2x12_cassette_options/
I did not think this way, but since Wolftooth got back to me and said a 12-speed Tanpan is not feasible, I am liking the idea of a 48/30 or 31 in the front with a wider range in the rear. Not quite as good as 46, but a bit more and certainly a lot less expensive.

Thanks for the idea.
1
Emilio700
56 posts
#5Jun 22, 2024, 9:28 PM
I had a similar idea but using a SRAM PG 11-44 cassette and Wolftooth Roadlink DM on 12s GRX Di2 2x. I have it working but shift performance isn't great. It will cross chain and still has RD tension when small ring x 13t cog. I suspect the shifting has more to do with the SRAM cassette than the config.

Prior to this I ran a full 2x GRX 11s Di2 with the same Wolftooth Roadlink but an XTR 11-40 cassette. Ran that for about 2 years and it shifted perfectly. Also allows cross chain no problem and no chain droop when small ring (31t) x 13t cog. Later I swapped in an 11-42t XT cassette and it still shifter perfectly. Trying to replicate that shift performance with the new 2x GRX 12s di2 but no luck yet. I'm doing the Oregon Trail Gravel 5 day stage race next week and wanted that super low climbing gear for the high altitude sections late in the race and also Crusher in the Tushar in July.

I might try the 10-45t Shimano cassette next. I can borrow the Microspline freehub off my XC bike and swap on to the gravel wheel set to test it. Both use DT 240 hubs so its a quick tool free swap. I'll post here if it works, unless John Z does it first.
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Emilio700
56 posts
#6Jul 10, 2024, 10:07 PM
It works!

https://youtu.be/m95zOSdvrPI?si=B4qomV1Zefcf03MT
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Emilio700
56 posts
#7Aug 19, 2024, 12:25 PM
Since this video I have swapped out the GRX 46/31 rings for Specialites TA 44/30 rings. Shifts better and the gear range is more useful. The 46x10 was too huge even for downhills. Someone commented asking to see the thing shift so I plan to do a short follow up video showing the full range shifting.

I'd say its perfect now. The only thing I wish I could do is draw the chainrings closer to the BB for a narrower chainline. This would make the 46x45 cross chain quieter although I only ever use that gear by accident. But going two cogs down to the 36t is pretty normal and I'd like to make that more efficient. I'd happily give up some efficiency in the opposite 30x14 combination.
0
stu
646 posts
#8Aug 24, 2024, 2:26 AM
For all kinds of reasons the small/small combination should be avoided. I don't intentionally use any cog in the small half of my cassette with the small chainring.
1
Emilio700
56 posts
#9Aug 24, 2024, 8:49 PM
For all kinds of reasons the small/small combination should be avoided. I don't intentionally use any cog in the small half of my cassette with the small chainring.
Yup. More an issue on a mechanical system where you can actually attempt that combo (and shouldn't). With Di2, the last two cogs are locked out.
0
John Z
174 posts
#10Aug 26, 2024, 9:31 AM
For all kinds of reasons the small/small combination should be avoided. I don't intentionally use any cog in the small half of my cassette with the small chainring.
Absolutely, but it is good to have for the unintentional moment. I follow a 3-cog rule, but my current 46-30 chainrings, and 11-40 rear XT (with a Wolftooth Tanpan) does allow for the complete range. Over the winter, I will switch to 48/32 with 11-46, per suggestions on this tread.
0
stu
646 posts
#11Aug 26, 2024, 12:49 PM
Absolutely, but it is good to have for the unintentional moment. I follow a 3-cog rule, but my current 46-30 chainrings, and 11-40 rear XT (with a Wolftooth Tanpan) does allow for the complete range. Over the winter, I will switch to 48/32 with 11-46, per suggestions on this tread.
I have a 2x9 setup which I made sure works in all combinations for safety reasons. After getting old and suffering a couple of semi-major crashes I no longer ride fast so I don't need small cogs. Also I can climb the steepest hills I encounter with a 1:1 ratio so I don't need a tiny chainring. My gearing is pretty simple since I need only about half the range in the thread title.
1
John Z
174 posts
#12Aug 26, 2024, 6:00 PM
I have a 2x9 setup which I made sure works in all combinations for safety reasons. After getting old and suffering a couple of semi-major crashes I no longer ride fast so I don't need small cogs. Also I can climb the steepest hills I encounter with a 1:1 ratio so I don't need a tiny chainring. My gearing is pretty simple since I need only about half the range in the thread title.
My "problem" is that I am still fairly powerful but even back when I was very powerful (FTP > 300 Watts before getting a mitral valve infection requiring open-heart surgery), I prefer to never have my cadence go below 70 RPM. Since I encounter climbs with double-digit grades, I need a very wide range.
0
stu
646 posts
#13Aug 29, 2024, 1:22 AM
My "problem" is that I am still fairly powerful but even back when I was very powerful (FTP > 300 Watts before getting a mitral valve infection requiring open-heart surgery), I prefer to never have my cadence go below 70 RPM. Since I encounter climbs with double-digit grades, I need a very wide range.
When I was in my 40s I could do only about 210 W for an hour on a rowing machine but I could climb double-digit grades in a 42-19 gear standing at a low cadence. 30 years later I'm much slower but still don't need really low gears. Even with a long top tube and 130 mm stem I tend to lift the front wheel climbing a steep grade seated so I usually stand.
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John Z
174 posts
#14Aug 31, 2024, 5:42 AM
When I was in my 40s I could do only about 210 W for an hour on a rowing machine but I could climb double-digit grades in a 42-19 gear standing at a low cadence. 30 years later I'm much slower but still don't need really low gears. Even with a long top tube and 130 mm stem I tend to lift the front wheel climbing a steep grade seated so I usually stand.
I am the exact opposite. I could also do at my peak 400 W for 4 mins and over 500 W for 1 min (in my 40s) but had no neuromusclular power and could not sprint to save my life. All my climbing is seated. I can only stay out of the saddle for like a minute max.
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