Shimano electronic shifting IGHs and ebikes (Di2)

[mrpelican]

Hi, I'm new to this forum. As I've been planning out my first ebike conversion, I came across the Di2 versions of Shimano's internally geared hubs (e.g. SG-S7051-8, but there are others). From what I've gathered so far, there are some advantages worth considering over the cable shifting versions. However, I have yet to find a documented ebike build using a Di2 hub. Discussion about this system seems pretty sparse in general, really.

The main benefits I see are:

• less (or no) adjustment necessary, which reduces the chance of damaging the hub mechanism from incomplete shifts
• the convenience of fast and consistent shifts
• possibly more options for the shifter to accommodate handlebar types and rider preferences

The first is the most salient for me. So is there a downside I'm missing that would explain why these hubs aren't talked about more in the ebike context? Here are the cons I can think of, but none of them seem like deal breakers:

• cost is a little higher than cable shifting
• if the Di2 motor stops working, you can't shift manually
• you have to charge another battery
• maybe the Di2 motor limits the cog options for adjusting the chainline in some scenarios

I'd love to hear some thoughts from others who have more experience in the ebike scene.

[ncmired]

I've no DI2 experience, but I have a lot of experience with the cable-operated 8-speed Alfine hubs. The majority of my bike builds have them, with no failures.

Towards your listed cons:

• if the Di2 motor stops working, you can't shift manually - I'm guessing the DI2 shifter motor would at least stay in the gear you're currently in, should "it" die. With the cable-operated hubs, should the cable or shifter break, the older hubs shift to 1st gear and the newer hubs shift to the highest gear. But you're correct, you'd be stuck in a gear. The Rohloff hubs handle the failover correctly.
• you have to charge another battery - since it looks look you can charge the shift motor via a USB cable, you should be able to connect to a powered USB port off of the bike motor's battery (built-in or via an in-line power cable adapter).

Towards your pros:

• less (or no) adjustment necessary, which reduces the chance of damaging the hub mechanism from incomplete shifts - this one concerns me - the DI2 shifter lets you shift anytime and you run the risk of damage IF you've got significant power applied. The nice thing about the cable (presuming shift sensor) is the motor power will be cut during the shift. This is more of an inexperienced rider behavior savior, but I'm pretty confident the 8 & 11 speed hubs won't survive a high power shift - and probably won't even be rideable.

Regarding the chain line, AFAIK the cable operated and DI2 hubs both use the same 3-tang cogs (flat and 3mm offset) - 16t to 23t in Shimano, with slightly wider gear range using Sturmey Archer cogs. In either case, the resultant 42mm/45mm/48mm chain line pretty much mandates the use of either Lekkie's 40T or Luna's 42T chainring.

[ncmired]

I got no use for hub gears. Its like a toy rather than robust hardware. Especially on an eBike. The eBike controller is in no way programmed to cater to a hub gears demands. eBike controllers have been hard on all the old school chain and sprocket systems. As well as the trusty freewheel setups that used to be good for the life of the bikes. So I can expect hub gears are going to have wear issues that the factories will be spending years trying to work out. In years maybe I will look at them again.

It depends on which IGH hub, and how treated.

The can do IGH hubs:

• the 3-speed Shimano and SA hubs do pretty well even behind major league power, and the SA CS-RK3 hub opens up the belt drive BBS02/BBSHD avenue pretty inexpensively. But their gear range is limited.
• the Shimano Nexus and Alfine 8-speed hubs can hang in there if treated nicely during the shift and give a not-bad gear range. I'm abusing my Salsa Marrakesh Alfine 8 equipped bike at 2.6KW regularly
• my Rohloff equipped bike is dealing with 3KW, and has built-in shear pins in case of going too far
• the Kindernay IGH hubs can deal with even more, as can some other IGH hubs due out shortly

The can nots:

• the SA 5-speed, the Shimano 7-speed, and most anything much older

Price-wise the 3 and 8-speed hubs aren't too bad, and the Shimano 11-speed is a where/when proposition, but the Rohloff and Kindernay are painful.

[mrpelican]

Have you seen the Nexus 5 speed? https://bike.shimano.com/en-EU/produ...-C7050-5D.html

Lower range than the Shimano 8 speeds (263%), but it's designed for ebikes, and the lowest gear is 1:1, which could be nice.

[ncmired]

Yep - seen it - the lowest gear being 1:1 is not a good match with the BBSHD (minimum 40T chainring), 700c wheel and a 28T (lowest) cog.
The gear inches work out to a pretty high 40-103. Works if you have 20" wheels. Also, there's only three cogs available (24-26-28), and they seem rare.

The CYC Photon motor with its 34T chainring - better, but still not good if you've got killer hills.

Forgot to mention I scrounge my SG-S501 hubs used, usually for $150 or so, and they're still holding up fine!

[mrpelican]

ncmired I had taken a look at your various Alfine 8 builds, so thanks for chiming in. Would it be accurate to say that your reason for sticking with the cable operated IGH is that it works well enough for you, and the perceived benefit of electronic shifting isn't enough to justify the added cost and system complexity?

Sounds like you don't see a big risk in the potential for grinding gears due to a cable that has fallen out of adjustment. Having never owned an IGH, I'm curious - how long does the cable adjustment usually hold for the Alfine 8? Is it easy to tell when it's time to adjust it? I worry about there being a point where the hub still seems to shift, but it is not perfectly engaged, and damage could be happening before you can tell that the adjustment is off. If all of this is less of an issue than I'm imagining, then maybe the cable shifting version would be just fine.

The newer hubs shifting to the highest gear if the cable breaks sounds like an unfortunate scenario, though pretty unlikely if you take care of the bike. I guess this is what they mean by the term "top normal"? And based on this video I found, I think if the Di2 motor fails, you're stuck in whatever gear it was in at the time. I think I could live with that, and those motors should last quite a while.

I will look more into the USB charging. That seems like a great solution.

From that same video, it's unclear whether you can do 2 shifts with one press, but it would be easy to tap it multiple times and shift more than one gear. To avoid shifting under power, I would probably use the green cutoff switch. Later on I'd consider trying to modify a Di2 shifter to output a cutoff signal automatically when you press the button.

For the chainline - I need to do some more reading about setting up single speed cogs, but I was imagining that the cog could be pushed outward with spacers if needed to match a chainring offset. Since the shift motor sits right next to the cog on the outside, it would be using up that space, and then chainline considerations may rule out the Di2 hub in some builds. I could be totally off about how the cog placement works though.

[ncmired]

ncmired I had taken a look at your various Alfine 8 builds, so thanks for chiming in. Would it be accurate to say that your reason for sticking with the cable operated IGH is that it works well enough for you, and the perceived benefit of electronic shifting isn't enough to justify the added cost and system complexity?

Some boring build history - my first e-bike build attempt was going to be a (TBD type) BBS motor with belt drive, and I had some hills to contend with. The Shimano 8-speed hubs had enough range, so I chose a fairly inexpensive Priority 8 (Nexus 8) with a grip shifter as the starting point. The base (non red band) Nexus 8 hubs are doggy (high drag) in 4th gear - enough you can feel it, so I found a used SG-S501 Alfine 8 (better planet gear bearings) and built a new wheel. The Nexus, Alfine SGS501, and related grip shifters are all "low-normal", and I prefer grip shifters because they have a specific gear indication number (easier for guest riders to deal with and somewhat easier to glance-determine what gear you're in). So, I kinda fell into what I've got, and kind-sorta stuck with it (and so far good luck) and kept the fleet consistent.

I like IGH hubs - no chain bending, and I use 1/8 chains for durability, slightly more drop protection, and a lot more weather protection (at least for the hub).

If Bafang worked with the IGH e-hub manufacturers like Bosch does, integrating shift sensing and auto-shifting down at stops, I'd be more interested in DI2.

Sounds like you don't see a big risk in the potential for grinding gears due to a cable that has fallen out of adjustment. Having never owned an IGH, I'm curious - how long does the cable adjustment usually hold for the Alfine 8? Is it easy to tell when it's time to adjust it? I worry about there being a point where the hub still seems to shift, but it is not perfectly engaged, and damage could be happening before you can tell that the adjustment is off. If all of this is less of an issue than I'm imagining, then maybe the cable shifting version would be just fine.

With the Shimano 8-speed low-normal hubs, the first indication of misadjustment occurs in 4th gear (jump or crunch at high power). The shift arm has two sets of matching easily read alignment marks, and the barrel shifters have a cable trim, so it's quickly taken care of. Usually everything beds in and settles down after the first few rides. You're correct - very critical:

So, on the low-normal hubs you shift up 3 clicks, and on the SG-S7001 high-normal you shift down 4 clicks - then align the marks. As it turns out, I don't ride the Alfine hubs much in 4th gear, as I try to gear the bike so that 5th (most efficient gear) is the go-to gear for most conditions.

The newer hubs shifting to the highest gear if the cable breaks sounds like an unfortunate scenario, though pretty unlikely if you take care of the bike. I guess this is what they mean by the term "top normal"? And based on this video I found, I think if the Di2 motor fails, you're stuck in whatever gear it was in at the time. I think I could live with that, and those motors should last quite a while.

I suspicion is first, the cable anchor bolt might slip/break, then second the shifter itself could fail.

I will look more into the USB charging. That seems like a great solution.

Easy-peasy

From that same video, it's unclear whether you can do 2 shifts with one press, but it would be easy to tap it multiple times and shift more than one gear. To avoid shifting under power, I would probably use the green cutoff switch. Later on I'd consider trying to modify a Di2 shifter to output a cutoff signal automatically when you press the button.

Something like that - could be complicated if there's a data stream of some sort. Who knows since it's Shimano.

For the chainline - I need to do some more reading about setting up single speed cogs, but I was imagining that the cog could be pushed outward with spacers if needed to match a chainring offset. Since the shift motor sits right next to the cog on the outside, it would be using up that space, and then chainline considerations may rule out the Di2 hub in some builds. I could be totally off about how the cog placement works though.

On these rotary shift hubs, there's no means to alter the chain line, other than what's available via the dish-in / dish-out cog configuration - there's just no room. The Kindernay suffers the same flaw, IMO. The Rohloff wins the chain line war, simply by being out at 58mm.

[ncmired]

This thread may be a good place to rerun this video on current and upcoming e-bike drivetrain designs from the Propel guy, who has quite a bit of industry insider connections and is a high-end U.S.-based e-bike vendor:

IMO, a lot of people are confused on how to operate bicycle derailleurs properly, and some were put off by them permanently. The issue was somewhat reduced by indexed shifters, but not completely - maybe because we've become an "automatic" society in many ways (including our cars).

While working in bike shops, I came across potential bike customers that were only interested in purchasing coaster-brake single-speed bikes - unsuitable for the local terrain, and that probably became flat-tire garage blockers.

[Retrorockit]

I'm running a 1x8 derailer setup that I think has most of the advantages of an IGH covered.
#1-Low normal derailer (Rapid Rise) with a grip shift (Revoshifter in Shimano speak).No 9 speed Revoshifters and 8 speed has become rare. Can down shift stopped or w/o pedaling. Shift happens next time you pedal. Never stuck in high gear after a panic stop. No reverse pattern trigger shifters available SRAM Shimano compatible grip shifts work, but the spring load is backwards and can be hard to upshift when wet.Derailers are pretty easy to find. Mid cage XTR in my case.
#2- Wide range 8 speed cassette. 11-40t. Sunrace is about $25. I toss it when the chain is worn. Required a longer derailer hanger to work with the Rapid Rise derailer. I cut and welded 2x stock hanger together. Extenders are readily available.
#3- Front freewheel mod. Shimano actually offered this once upon a time. Magic Cranks still does. Mid drives all have a front freewheel. If you lock out the rear one with a couple small zip ties it become the primary one way clutch. Shift w/o pedaling. Multiple gears up and down. Any time the wheel is turning you can shift. Pause pedaling cuts power and releases the clutch.Pretty much like driving a stick shift car or moto. Requires a top roller chain guide. I'm still working out the best way to do this. Any chain suck event the zip tie breaks and the bike returns to normal.Could probably do w/o Rapid Rise since downshifts are so easy in real time. But I already have it.
Here is the thread on this. A modern clutch type derailer would probably help (Sunrace M900?). But I've been riding it this way for a few months now.

https://electricbike.com/forum/forum/main-forum/diy-discussion/156222-mid-drive-cassettte-zip-tie-mod

As far as electric shifting goes- I can replace a broken cable myself...........
When a cable breaks I can stick a rock or twig in the derailer linkage and ride away in whatever gear I want.

To be fair I was already running Rapid Rise years ago, and already had some of these parts. It was already there when I added the BBSHD. But I still upgrade things now and then with parts form the internet. My XTR derailer and Revoshifter are both recent purchases.

[Retrorockit]

I'll throw another IGH into the discussion The Nuvinci 171B. Apparently there are electric shift versions out there somewhere. Strong,cheap, light. Pick two.

https://cycles.eco/products/nuvinci-n171-cvt-hub-manual-shifting-version?variant=

[mrpelican]

Regarding the chain line, AFAIK the cable operated and DI2 hubs both use the same 3-tang cogs (flat and 3mm offset) - 16t to 23t in Shimano, with slightly wider gear range using Sturmey Archer cogs. In either case, the resultant 42mm/45mm/48mm chain line pretty much mandates the use of either Lekkie's 40T or Luna's 42T chainring.

I'm finally getting around to digging into the chainline options. How did you come up with 42/45/48mm for the cogs? This is a bit different from what I find on Sheldon Brown's site (43.5/46.5/49.5), https://sheldonbrown.com/chainline-internal-gear.html (2nd table).

Also, I found that the Shimano dealer's manual for these hubs has quite a lot of useful information. For example, it tells you that of the 3 Di2 motor options, only MU-UR510 allows you to use both dished-cog orientations.

[ncmired]

Hi - I can't remember where I initially memorized the values from, sorry. Glad they're farther out, even ever so slightly. Can you post that DI2 link for future reference - that dish limitation hurts DIYers, at least those who would choose 1/8 chains. Thank you for the correction.

[Retrorockit]

Shimano Made a 5 speed Di2 Ebike hub with all overdrive gears except first which was 1:1. They had to offer some larger cogs for this but they have 6 drive tabs instead of 3. But they come in 30,27,and 24t sizes.
It's in the gear chart here.

https://si.shimano.com/en/pdfs/dm/CASG004/DM-CASG004-02-ENG.pdf

[mrpelican]

Alfine Di2 manual: https://si.shimano.com/en/pdfs/dm/S7...051-05-ENG.pdf
If that link stops working in the future, you can search by model number on the Shimano documentation site.