46/34 & 11-40T Di2 custom drivetrain

Finally got my mix n' match 2x11 drivetrain working smoothly. 493% ratio spread with excellent spacing. For reference, SRAM 1x12 (42x10-50T) is 500% For gravel races that have less climbing, like Dirty Kanza, I run an 11-32 cassette which is plenty there. But for Rock Cobbler, Crusher, BWR where sustained 15% pitches are part of the proceedings, that 23.5 gear-inch bottom is lovely.

Dura Ace 180mm R9100 cranks with power meter
46T Ultegra R8000 chainring
34T Ultegra R8000 chainring
HG901 XTR/DA chain
R9100 Dura Ace FD
RX805 RD
Dura Ace R9170 shifters
13T upper jockey pulley, Amazon/China special ( OEM is 11T)
Wolftooth Roadlink DM

Before the 13T pulley and Roadlink, it would skip in the 46x11 at around 250 watts due to insufficient chain wrap around the 11cog. 13T pulley bumped that to about 300 watts. Roadlink eliminated skip at any wattage I can produce.

Shifts fast and smooth up or down. Oddly, I can shift from inner to outer ring under full power in this set up but my road bike with R9100 won't quite do it. Quiet even in 46x40. Only time I get excess chain bounce is on eyeball ratting 30mph rocky descents when I forget to shift down from 11 cog. Overall I wish I had a tiny bit lower bottom gear, maybe 22 gear-inches but I wouldn't want to give up my top gear. As good as this is, I'd wish for another 2 gear inches lower and a stiffer clutch if I could.

GRX 815 RD (2x) is long cage but rated for 34t max cog. GRX 817 RD (1x) rated 42t max cog but is mid cage. So oddly, the older RX805 is a better solution. In theory, the XTR Di2 RD would easily handle the 40T and have enough cage for a 2x but Shimano e-tube software won't let you mix road and mtn derailleurs. I actually tried to make a mount for my braze on fd mount to fit an XTR FD to get around this, but my 3D printed mount wasn't nearly stiff enough.

Reference numbers, my set up compared to a 1x12 SRAM setup with similar low and high gear.
46x11 115.5 gear-inches with 40c
34x40  23.5 gear-inches with 40c
52x12  114.5 gear -inches with 25c
32x50  18.5 gear-inches with 29x2.25"

Jump between two biggest ratios
46x11-12  9% jump (my stuff)
42x10-12 20% jump (SRAM 12s)

Jump between two smallest ratios
34x35-40 14% jump (my stuff)
42x42-50  19% jump (SRAM 12s)


   

I don't understand why you didn't go with a 46/30 crank and an 11-36 cassette. You get a slightly wider range, tighter gear spacing and a simpler setup without the roadlink.

180

bnystrom wrote:I don't understand why you didn't go with a 46/30 crank and an 11-36 cassette. You get a slightly wider range, tighter gear spacing and a simpler setup without the roadlink.

I run 180mm cranks with dual sided power meter. No dual-sided 180mm crank exists that will accept a 30T ring. I ran 180mm  Rival 10s cranks with a Stages left side from 2015 until I built this, 5x110bcd but also 34T min ring size.

In any case, when you increase the front chainring spread the RD still has to take it up. There is another fellow on this forum that is looking for the same phantom 2x crank that will accept a 28 or 30T.

Emilio700 wrote:180

Emilio700 wrote:
I run 180mm cranks with dual sided power meter. No dual-sided 180mm crank exists that will accept a 30T ring. I ran 180mm  Rival 10s cranks with a Stages left side from 2015 until I built this, 5x110bcd but also 34T min ring size.

OK, I've never looked for 180mm cranks, so I'll take your word for that.

In any case, when you increase the front chainring spread the RD still has to take it up. There is another fellow on this forum that is looking for the same phantom 2x crank that will accept a 28 or 30T.

I'm not sure what you mean. There are several cranks that are available with 46/30 chainrings, in lengths of 175 or under.

Yup many 2x 46/30 options with single-sided power meter. None of those can be had double sided, which is what this other fellow was looking for.

Emilio700 wrote:Yup many 2x 46/30 options with single-sided power meter. None of those can be had double sided, which is what this other fellow was looking for.

Emilio - have you seen the Fit Link from WickWerks?  May lower you FD and be stiff enough for your purposes.  So long as they make a braze-on XTR Di2 FD...
https://wickwerks.com/products/fit-link-adapter/

No braze on XTR FD exists. I got the drive train working flawlessly in any case. I'm greedy though, wouldn't mind having like 520% range for a 20 gear inch low gear 🙂

I had a similar dilemma to you. I've tried 1X set ups and decided they weren't for me. I wanted low gears for climbing but didn't want to compromise on the top end too much. 

My my solution was to mix Dura Ace & XTR Di2 with a bit of Sram XX.  Levers are Dura Ace, cranks are XTR 985 44/30, mechs are XTR and the cassette is a 10-42 XG1199. 

This is gives me a low of 19.2" and a top of 119", a range of 616%. Shifting is flawless in all gears with no need to resort to extra links etc. 

 

The biggest gear I used back when I was racing was 110" and I don't need that anymore. The 46x12 gives me 103.5", which is more than I need for gravel and essentially the same as the 50x13 / 103.8" gear I use on the road. Likewise, I find that the 25" low gear is fine for all but the steepest MTB trails.

bnystrom wrote:The biggest gear I used back when I was racing was 110" and I don't need that anymore. The 46x12 gives me 103.5", which is more than I need for gravel and essentially the same as the 50x13 / 103.8" gear I use on the road. Likewise, I find that the 25" low gear is fine for all but the steepest MTB trails.

The 10 & 12 sprockets are more for use on tarmac. However the 36 & 42 allow me to climb on steeper loose surfaces more easily. Having limited movement in one ankle means pitches of 15%+ especially on gravel are problematic. Sometimes it's just nice knowing I have the option, other times it's needed. The final climb of GF Strade Bianche is a nasty 12% average with the last 50m at 18%. The last time I rode it I hade 36x32 and it was not a pretty sight!  Zigzagging out of the saddle was the only way up without losing grip. His year saw able to climb seated straight up. 10' slower but far less pain in the mangled ankle. 

Nice work, guys.  I love seeing creative solutions like these.  The 46/34 front combo is one I like, too, albeit on my road bike.  The 12T difference in rings mitigates the need for extra shifting on the back when switching, which is something I found clumsy with a 50/34 combo.

I just had the GRX Ultegra 48/31 and 11-40 put on my Roker and loving it. The only thing I noticed is when you switch from the low gears to the high you pretty much have to go to the lower gear in the high ring. That hasn't been a problem for me though. My LBS had to call Shimano and had to put different calipers on it because of my bike being either post mount or frame mount brakes. All a foreign language to me.

RX810 raze front end derailleurs
RX810 rear derailleur long cage with clutch
disk brake assembled set/j kit direct rx810 left and right
FD-R9150 froint derailleur braze on adaptor 34.9 mm
HG701 chain with quick link
bottom bracket parts MT800-S right and left adaptors
XT CS-M800 cassette 11-40t
RS785 caliupers
Also had lizard skins handle bar tape on.


Zman

Zurichman wrote:I just had the GRX Ultegra 48/31 and 11-40 put on my Roker and loving it. The only thing I noticed is when you switch from the low gears to the high you pretty much have to go to the lower gear in the high ring.

I helped a friend get his 2020 Domane SL set up with similar range to mine. He has the same 11-40 cassette but a 50/34 Ultegra crank. So he faces a similar jump between large and small chainrings when shifting as you do. It's a tradeoff. Greater range vs a bit more awkward front shifts. Personal choice I guess.

Emilio700 wrote:
I helped a friend get his 2020 Domane SL set up with similar range to mine. He has the same 11-40 cassette but a 50/34 Ultegra crank. So he faces a similar jump between large and small chainrings when shifting as you do. It's a tradeoff. Greater range vs a bit more awkward front shifts. Personal choice I guess.

It seems to me that the real question is does he actually need a 50 x 11 (123") top gear. Most people can't really push a gear that big on the road unless they're going downhill with a tailwind, and it's even less likely on gravel.

Maybe he's a beast can can actually use that big of a gear, and I understand that we all want to think of ourselves as bike studs, but being realistic has it's advantages. In this case, it would be better shifting.

I find it interesting that some folks here have concerns about making double shifts (up in the front and down in the back simultaneously, or vice-versa). It's not difficult and once you've done it a few times, it becomes second nature. It's just a skill that every rider should develop. Heck, back in the day, we used to do it with downtube friction shifters. By comparison, doing it with indexed brifters is about as difficult as flipping a light switch.

Emilio700 wrote:
I helped a friend get his 2020 Domane SL set up with similar range to mine. He has the same 11-40 cassette but a 50/34 Ultegra crank. So he faces a similar jump between large and small chainrings when shifting as you do. It's a tradeoff. Greater range vs a bit more awkward front shifts. Personal choice I guess.

Emilio some inner net problems here at my end. I have only had the GRX out on 2 runs so far because of the cold weather here in PA. This is what I kind of saw on my first time out on the GRX. I gained 3-4 or possibly 4-6 mph on the top end. On the old Sram 1x I was lucky to hit 24 mph o the flats i high gear. On the lower end with the 31 x 41t the sky is the limits as to what I can climb in the low gear. I will have no problem with the shifting from the low to high gear as i pretty much worked it out on my first ride. I do know that I wouldn't have been able to finish the Southern Cross ride in the old Sram set up as I was using that what I call the low bail out gear a lot. It looks to be a game changer to me.

Zman

bnystrom wrote:

It seems to me that the real question is does he actually need a 50 x 11 (123") top gear. Most people can't really push a gear that big on the road unless they're going downhill with a tailwind, and it's even less likely on gravel.

He doesn't. Agreed, but he's on a tighter budget than I am. Mine is 46/34 and I'm much stronger than he is. I'm trying not to force him into equipment expenses unless they are absolutely necessary. I explained that he could stay in the big ring longer whenoff road but he seemed to be OK with the 50T after a few rides. He's not a bike geek like I am so it might just not register.

But yeah, so many gravel riders are just a bit too macho for their own good. I mention to riders that aren't nearly as strong as I am, what my gearing is and they always say something about "I don't want to spin out" or some such nonsense. I'm data driven. I look at my actual cadence on rides, where I suffered, where I got dropped (or opened a gap). Unless you're a pro on fairly level ground, you probably don't need a 50T.

It's not unique to gravel riders by any means. Roadies and MTB riders are no different. I have to chuckle at all the people I see on road bikes with 53/11 (130") top gears. Most of them probably haven't used them in years and they're just a waste. I'd rather have gearing that I will actually use on a reasonably regular basis. That said, my 50/13 doesn't get used much on the road, as winding that out means I'm doing ~35mph. That only happens going downhill and at that point, I'm better off to tuck and coast.

bnystrom wrote:It's not unique to gravel riders by any means. Roadies and MTB riders are no different. I have to chuckle at all the people I see on road bikes with 53/11 (130") top gears..

Yup. I was 3rd at road Nationals last year on a 52/36 x 11-30T. Two guys up the road, 8 of of us chasing. I out sprinted a former individual pursuit world champion (on a 53x11) with my 52x11. Topped out at 44.7mph about 100m out, seated. So yeah. precious few road riders actually need a 52, let alone a 53.

I have always heard that racers could spin out a guy on 1x if they had 2x gearing. After just a few rides on my 48/31 and 11-40t I can see that. I am really impressed with the top end speed I got there with the GRX 2x compared to the 1x Sram Rival 1. To me it's seems like a game changer. The low 31 x 40 which I will call my bail out gear seems like there will be nothing I can't climb unless it's that steep that it's a hike a bike. I am far out of shape right now and can't wait to get back in shape and see what it can do then.

Zman