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Di2 options for a gravel bike?

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Di2 options for a gravel bike?

Old 07-02-22, 05:08 PM
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Polaris OBark
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Di2 options for a gravel bike?

I bought a titanium frame (Sage Barlow) to build up for my wife, and I have a set of Di2 ST-R785 /BR -RS 785 11-speed shifters with (post-mount) hydraulic calipers. (This was the first generation of hydraulic 11-speed Ultegra/DuraAce Di2, from about 2014. I have a set on my bike, and this was $199 at Universal Cycles a couple of years ago, so I snagged it for a spare or some future project.)

The good news is that according to Shimano's E-tube Project Compatibility Chart, these will worth with 11-speed Ultegra/DuraAce, XT(R), and GRX derailleurs.

My wife has degenerative knee and hip joints (probably osteoarthritis) and she started riding an e-bike, but really wants to do some more conventional riding before the clock runs out. She needs some easy gearing and is unlikely to be the next Lael Wilcox. I'm riding a GRX 46/30T crankset with 11-36T cassette, Di2 Ultegra shifting throughout. I'm considering options for her, thinking she should be able to go at least as low as 30T F 36T R. I have an extra 46/30T GRX crankset that I could use "for free", which would make some of the options below a bit less costly. Since the cost of battery, etc will be the same for all of these options, I am focusing only on derailleurs and cranksets...

So, here is what I am seeing as possibilities:

A. Ultegra 2X
Repeat of what I have. Front/Rear Derailleurs $530 + free crankset.

B. GRX 2X
Very similar. Front/Rear Derailleurs $540 + free crankset.

C. GRX 1X
One derailleur: $335 + cheapest GRX 1X $150 = $485
Lowest gear (40T F x 42T R) will actually be considerably higher than options A and B. Could find a smaller 1X crankset.

D. XT mountain gearing (which is compatible with the Di2 road shifters)
Front Derailleur: $50 [sic] + Rear Derailleur $280 = $330 (or go 1X and save $50)
I found an XTR double (new, non-boost), 36T/26T for $140. The only downside is 175mm crank arms (harder on knees, precludes 650b wheels). Would allow VERY low gearing while going almost as high as a 40T 1X.
Total $470.

E. Forgetaboutit and go Mechanical
Nearly infinite options, very few parts.

What say you?
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Old 07-02-22, 05:12 PM
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One other issue: I can't use a crank with a 30mm spindle because there is not enough room in the BB shell with a Di2 wire.



If you want to play around with the gear ratios, this link is a starting point.



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Old 07-02-22, 09:03 PM
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I壇 probably vote for option B, since it will get the low gearing you池e after and the GRX front derailleur is guaranteed to work with your GRX crankset. However, if you think that she will eventually need even lower gearing, then option D looks pretty attractive. (I doubt that a few extra millimeters on the crank arms will cause much trouble to your wife痴 knees. Though obviously I may be wrong about that.)
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Old 07-02-22, 11:22 PM
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I have 2 gravel bikes. 2x and 1x. I find the 2x comes into it's own as a dual purpose bike. slap on some carbon wheels and gp5000 road tires and try and keep up with my road buddies.

1x is perfect if you are not racing, chasing pr's, trying to keep up with faster people.

I am thinking with your wife's knee she probably not trying to go real fast for extend periods of time so 1x would be better. it's so easy and cheap to buy a different 1x chainring for $20 to $30. Get a 11-36 or 11-40 for the back and experiment with how low of gear you need for hills / top speed.

https://www.bikecalc.com/gear_speed

says 40t front 11 back with 32mm tire 90rpm is good for 26mph. so you can probably even drop the front gear to a 38 or 36. Unless you and your wife like to bomb down hills.
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Old 07-02-22, 11:49 PM
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If using the crank and chainrings you already have is the goal, then go with option B, IMO. The clutched RD will keep things running nicely, and keep the chains where your wife will want them, on the cogs...it’s not just for 1x.You know your wife’s capabilities, and if you think your 46/30 mated to an 11-36 will work for her, this is a pretty simple upgrade beyond the cash and your time.

Also, there are more than a few people 'round here who have used their GRX 2x way outside Shimano’s spec to get an 11-40 cassette to work with the RD-RX810 (same body and mechanical geometry as the Di2 RD-RX815). I am not a fan of doing it for the simple fact that the B-screw is fully turned in to clear the big cog on the cassette. The only issues may be chain wrap on the extreme gearing combinations, but you can sort of lock out those options.
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Old 07-03-22, 02:52 AM
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Option B for sure. A 30 inner chainring and a 36 large cog on the cassette is good for 4 mph at a 60rpm cadence. Most people can't keep a bike upright below 4 mph.
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Old 07-03-22, 09:03 AM
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On the hill where I often use my 30/36T low combo, I get well below 4 mph, and my Garmin auto-pauses sometimes. And yes, I do "need" that gear sometimes, especially at the end of the day, on the 20% grade. (This is where she "needs" the e-bike.)
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Old 07-04-22, 12:45 PM
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How fast does your wife want to go? Does she draft you and pedal fast down hill? 30+ mph ?

If you get the Rear Derailleur Shimano GRX RX812 Shadow Plus ( meant for 1x ) it will do 11-46T pair that with a 32T front she can climb probably anything and it's still good for about 20mph.

You might even be able to go bigger. My Ibis MX gravel bike came with a 11-46T from the factory. They probably on the conservative side.
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Old 07-05-22, 04:52 PM
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Originally Posted by sean.hwy View Post
How fast does your wife want to go?
​​​​

Not very.

​​​
Does she draft you and pedal fast down hill? 30+ mph ?
No.

If you get the Rear Derailleur Shimano GRX RX812 Shadow Plus ( meant for 1x ) it will do 11-46T pair that with a 32T front she can climb probably anything and it's still good for about 20mph.​​
Trick is finding that. Or I could get the XTR crankset, and she would have a bail gear. The $50 XT Di2 front derailleur is thus a temptation.

​​​​​​​You might even be able to go bigger. My Ibis MX gravel bike came with a 11-46T from the factory. They probably on the conservative side.
Shimano is definitely on the conservative side when rating their derailleurs. My Ultegra is rated for 32T max and handles 36T with no issues.
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Old 07-06-22, 07:37 PM
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Osteoarthritis is hardly a death sentence. I know people with bilateral knee and hip replacement and are happy.

Build her the bike she wants to ride and let her rebuild herself when she needs it. Who knows, maybe a fun bike will even put off those interventions a little longer.
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Old 07-06-22, 07:59 PM
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Originally Posted by rosefarts View Post
Osteoarthritis is hardly a death sentence. I know people with bilateral knee and hip replacement and are happy.

Build her the bike she wants to ride and let her rebuild herself when she needs it. Who knows, maybe a fun bike will even put off those interventions a little longer.
That's exactly what we are hoping for, and why I got the frame.

The funny thing is she is now becoming a weight weenie.
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Old 07-07-22, 12:56 PM
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Why not 1x with bailout..44/28 w/ an 11-36 or 11-42
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Old 07-07-22, 08:21 PM
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Our tandem is running 46/30 front and 10-42 rear with GRX di2 and the same BR -RS 785 shifters. I added a RoadLink DM which avoids the need to adjust the B screw to it's limit. Shifting is perfect. And we are often going 2.5 mph on gravel climbs in New England and have never fallen over! So I'd go with option B as well. IMHO 1X on gravel is a compromise with no real gain - but that is an argument for another thread!
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Old 07-11-22, 04:53 PM
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Originally Posted by Germany_chris View Post
Why not 1x with bailout..44/28 w/ an 11-36 or 11-42
That would be perfect. Any suggestions for a 44/28 ?
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Old 07-11-22, 04:54 PM
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Originally Posted by Chilepines View Post
Our tandem is running 46/30 front and 10-42 rear with GRX di2 and the same BR -RS 785 shifters. I added a RoadLink DM which avoids the need to adjust the B screw to it's limit. Shifting is perfect. And we are often going 2.5 mph on gravel climbs in New England and have never fallen over! So I'd go with option B as well. IMHO 1X on gravel is a compromise with no real gain - but that is an argument for another thread!
Sorry I missed this. That is really helpful.
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Old 07-12-22, 02:18 AM
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Originally Posted by Polaris OBark View Post
That would be perfect. Any suggestions for a 44/28 ?
I'd do it with a TA Carmina but then you'd need to go back to square taper.

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Old 07-12-22, 08:10 AM
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Originally Posted by Germany_chris View Post
I'd do it with a TA Carmina but then you'd need to go back to square taper.
I've got a white industries crankset on another bike -- maybe I could use that.
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Old 07-12-22, 08:43 AM
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Originally Posted by Polaris OBark View Post
I've got a white industries crankset on another bike -- maybe I could use that.
It seems like a VBC could make that happen and probably with less pain.
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Old 07-12-22, 09:24 AM
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Originally Posted by Germany_chris View Post
It seems like a VBC could make that happen and probably with less pain.
The 30mm spindle won't fit if I route a Di2 wire through the BB, so I would have to use square taper. (Once I got rid of the White Industries bottom bracket and used instead a Shimano, it works fine).
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Old 07-12-22, 12:24 PM
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Originally Posted by Polaris OBark View Post
The 30mm spindle won't fit if I route a Di2 wire through the BB, so I would have to use square taper. (Once I got rid of the White Industries bottom bracket and used instead a Shimano, it works fine).
How does the cable route?

WI bearings sit at the cup and Shimano uses a cartridge it would seem it壇 be easier with the WI BB.

You could also use an SKF

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Old 07-14-22, 10:42 AM
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Originally Posted by Polaris OBark View Post
The 30mm spindle won't fit if I route a Di2 wire through the BB, so I would have to use square taper. (Once I got rid of the White Industries bottom bracket and used instead a Shimano, it works fine).
I have White Industries G30 crank with their BB with 30 mm spindle, and have three di2 wires running through the BB (seatpost battery, FD and RD). I did something most people would not want to do - customized the wires to avoid using the B-junction - but I think the standard di2 wires would fit as well.
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Old 07-22-22, 07:34 PM
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I went for option B.

I'm already ahead since I have a GRX 46/30T crankset. Bike Tires Direct is having a 25% off sale today on any one item in your shopping cart. Amazingly, it doesn't limit you to one purchase, so I got 25% off on front and rear Di2 GRX derailleurs, and front and rear flat-mount calipers (I found out the hard way I can't use my NOS post-mounts in the rear -- even with the right adapter, and the front looks stupid, so I am getting those and will keep the post-mount calipers as spares.)

If her gearing isn't low enough, I can easily put in my White Industries crankset that is on my touring bike, and get a really small inner ring, or Wolf-tooth it in the rear.
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Old 07-29-22, 01:34 PM
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Well, I am now in possession of the levers/shifters(ST-R785), GRX front and back derailleurs, a battery (BT-DN110), and a primary junction box (on the way). I bought the junction box with 5 ports (SM-EW90-B) in case I want to use just that and no secondary junction, but am now having second thoughts about running three(?) parallel cables to the stem.

Although I have had Di2 on my own bike since 2014, I have no experience putting it together from scratch.

The frame is drilled for the cables, so that shouldn't be an issue, and I plan to put the battery in the seat post (or tube)
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Old 07-29-22, 08:28 PM
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You are also going to need a bunch of di2 wires. Without a B junction, putting the battery in the seatpost may be a problem because you need additional length to be able to get the post out. If you want the di2 to talk to a head unit or your phone, you will also need the Bluetooth module.
As I wrote in a previous post, it is possible to run di2 wires around a WI bottom bracket with a 30 mm spindle - just barely.
It's not that likely that you can get a B-junction into the downtube
I've recently set up a tandem and gravel bike, both steel frames and it's not really hard, but it can be a bit intimidating with all the wires.
BTW - I have a few di2 wires and a B-junction left over that I'd like to unload!
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Old 07-29-22, 08:40 PM
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I've got a GRX crankset in there now, so no issues with BB clearance. I think for aesthetic reasons as well, I will use a B-junction.

I'm assuming I need a (long) wire for the battery in the seat post, a long one to go from Junction A to Junction B somewhere near the BB, and a short one to the front derailleur, two approx 350mm wires for the shifters, and one for the rear derailleur. I've lived without the bluetooth module since 2014 on my other bike, so probably will skip that for now.

That's one B-junction box and five wires. I need to get some good estimates for the lengths, and then maybe I can take you up on your offer. (The down tube is 700mm, the seat tube is 500mm + slack to permit pulling it out easily, the chain stays are 422mm.)

Also, I know there are different wires for 12-speed vs. 11-speed, but within the 11-speed family, are there two different e-tube ends, and are they compatible? The GRX derailleurs are a lot newer than the levers and Box A.

I've been reading up a bit here: https://bettershifting.com
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