Largest Di2 chainring size?

[LittleWheelsandBig]

I'm looking at possibly setting up HK's Moulton with Ultegra Di2 but the bike needs to run at least a 58t big ring. Is this possible?

Also what is the widest practical difference between the two rings? At the moment, she has 58/48/34 rings and 11-25 cassette on a 3 x 10 Campag setup.

SRAM's eTap doesn't look to have long enough range between charges, beside an excess of batteries. Campag is off the list entirely.

[Thing2]

We had a 19 tooth difference between the two chain rings with di2 on the orange tandem without any issues. It was 52/33 though with SRAM red chainrings. I've no idea whether 58 is possible though or whether the ramping on the chain ring would impact how well it shifts between them.

[LittleWheelsandBig]

It'd be a ramped and pinned ring in any case. I was hoping to match it to a 42t or perhaps a 39t.

[quixoticgeek]

Officially if you ask anyone from Shimano, they will say max 16t difference at the front. However in the real world you can often get a bit more.

J

[Brucey]

worth mentioning that the limit is often the chain rubbing the bottom of the FD cage when running small-small. However this

a) isn't a gear that you should be using anyway and
b) the exact point at which this occurs varies with exactly how the FD is mounted, i.e. from frame to frame.

Often you can get a bit more 'capacity' by installing a wedge spacer between the FD and the braze-on. On a moulton the FD can be mounted slightly further ACW than normal (as viewed from the RHS of the bike) because the biggest sprocket doesn't have to be that large to get the gear range that is required, and the chain is unlikely ever to be 'too high in the FD' even when running big-big.

cheers

[Kim]

worth mentioning that the limit is often the chain rubbing the bottom of the FD cage when running small-small. However this

a) isn't a gear that you should be using anyway and
b) the exact point at which this occurs varies with exactly how the FD is mounted, i.e. from frame to frame.

c) may not happen when the chain is under real load, rather than bouncing around as it's cranked in the workstand

I get rub on my tourer (recumbent, so the usual chainline concerns don't apply) when it's unloaded or if you backpedal, but if you're actually using the granny ring for its intended purpose, the tension in the chain keeps it clear of the cage.

[LittleWheelsandBig]

According to Moulton, I have a good chance of this working. The major hassle is working out where to fit batteries (possibly inside the head tube) and junction boxes and how long the connecting cables need to be.

[Brucey]

big fat seat tube on many moulton models; could you put the battery in there?

cheers

[grams]

If the problem is getting the cable inside, if there’s even a small hole available you can cut a cable in half and feed it through. Di2 cables are just a skinny two core cable inside, so very easy to rejoin.

[LittleWheelsandBig]

I'm not sure that an internal battery is an advantage in this instance. The external battery can be removed/ replaced and charged separately from the bike. That could be an advantage during a long brevet.

A major concern is separating/ packing the bike for TGV/ bus/ airplane travel, so I don't want to have too much opportunity to damage cables while turning handlebars, splitting the bike, etc. If eTap lasted through a 1200 without charging, I might have picked that option.

[Hot Flatus]

Take a cable on the Brevet. Plug in the main junction box (usually mounted under bars) whilst at control or a cafe. Remember you get about 1000 miles after each charge, so a quick top up would do it for all but the longest.

Plenty of people will have experience of packing di2 for foreign sportives etc, so it might be worth asking for tips on a more forward thinking forum 

I think Karla has Etap. Might be worth a chat.

[grams]

The advantage of the internal battery are that it’s (potentially) easier to mount and route  and it’s less ugly and doesn’t get in the way. It can also be charged off USB (e.g a power bank) whereas I think the external one requires mains, and therefore the charger you carry is much smaller.

(The third option is mounting an internal battery externally, which Shimano sell a case for - I actually have a spare unused one of these to shift if you’re interested)

[Torslanda]

eTap 'lasting thru a 1200'?

I'm no expert - only fitted one set to a tribike - but the instruction video refers to a battery life measured in months...

[jiberjaber]

I'm not sure that an internal battery is an advantage in this instance. The external battery can be removed/ replaced and charged separately from the bike. That could be an advantage during a long brevet.

A major concern is separating/ packing the bike for TGV/ bus/ airplane travel, so I don't want to have too much opportunity to damage cables while turning handlebars, splitting the bike, etc. If eTap lasted through a 1200 without charging, I might have picked that option.

You won't be able to charge the internal battery separate from the bike without a set of almost the same cables you already have on the bike! (So external charging would require a junction box A (where the charger plugs in) and then a cable between that and the battery. 

There's not a bad diagram on this site: http://www.theeverydaycyclist.co.uk/2017/05/01/trek-madone-di2-upgrade/
(Ignore the WU101 unit if you don't want to connect the DI2 to your Garmin Edge or update it through bluetooth?)

You can put the battery wherever within the frame that suits your needs, multiple 4-way junction boxes could be used (they are just a 4 port common connection with no electronics inside them) 
There are a few options around "Junction Box A" some are just a variation on the number of switches that can be connected (i.e. 4 port or 5 port) or mounting configurations (i.e. the traditional under the stem mount or as a bar end plug or as a special 'in frame' mount, the later needs a frame with a specific shaped cut out in it.)

In terms of charging, I just topped mine up once during LEL - it took about an hour and I did it whilst moving.  You do need to carry the charger block with you to do this (it is just a USB device but slightly bulky 



This thread is the second time I have seem people advocate cutting a DI2 cable to allow fitting.  I would caution against this, the cable is of a construction that is similar to a silicon coated headphone cable so rejoining for a reliable connection is going to prove to be a very skilled job resulting in a joint which is probably larger than the cable end connector.  I would not trust such an unsupported (as in the cable not being attached to anything within the frame) joint on multiple 200km rides let alone a 1000km brevet (and I am quite handy at the soldering cables game!)

[quixoticgeek]

eTap 'lasting thru a 1200'?

I'm no expert - only fitted one set to a tribike - but the instruction video refers to a battery life measured in months...

It is worth noting, that the total operating time for your average 1200 audax is about the same amount as many cyclists ride in a whole season.

I get this with my Wahoo sensors, I'm riding for so many hours that the supposed 1 year battery life is actually closer to 4 months.

It annoys me that companies list their battery life in times of months, rather than operating hours...

J

[FifeingEejit]

When it comes to charging the Di2 a suitably beefy USB battery pack is able to charge it, didn't think it was possible while moving unless you go without gears but since I've got the bar mounted Junction A it's a bit trickier to hook up to the battery pack.

I've had a full charge from my PowerMonkey Explorer 2; it used about 10% of the battery capacity IIRC, which is less than my Wahoo takes (about 20%) and way less than the Lezyne Super GPS (about 60%) but since I've had about 1500km worth of gear changes with a mix of hilly and flat, and my tendency to use all available gears the chances of running out of gears during an Audax that doesn't involve more than 1hr charge time snoozing or sleeping seems minimal.
The challenge there is getting more power into the battery pack as it does need more than the Di2's 1hr...

For splitting the bike with internal routing an appropriate choice of cable lengths and junction box although slightly more expensive would make sense; preventing the cables and junction box from disappearing down the tubes may be a tad trickier!

[quixoticgeek]

When it comes to charging the Di2 a suitably beefy USB battery pack is able to charge it, didn't think it was possible while moving unless you go without gears but since I've got the bar mounted Junction A it's a bit trickier to hook up to the battery pack.

I thought you could charge it while you ride, but you lose the water proof integrity of the junction?

I've had a full charge from my PowerMonkey Explorer 2; it used about 10% of the battery capacity IIRC, which is less than my Wahoo takes (about 20%) and way less than the Lezyne Super GPS (about 60%) but since I've had about 1500km worth of gear changes with a mix of hilly and flat, and my tendency to use all available gears the chances of running out of gears during an Audax that doesn't involve more than 1hr charge time snoozing or sleeping seems minimal.
The challenge there is getting more power into the battery pack as it does need more than the Di2's 1hr...

The internal battery pack for Di2 is 3.7Wh. If you have a standard 3W dynamo hub, running into a USB-Werk unit, you can get approximately 2.5Wh for every hour of forward motion. Charging this into a battery pack to then put into the Di2, you can expect some loses, so better work on 2Wh per hour of motion, giving you 2 hours to put into the battery pack enough power to charge your Di2.

For splitting the bike with internal routing an appropriate choice of cable lengths and junction box although slightly more expensive would make sense; preventing the cables and junction box from disappearing down the tubes may be a tad trickier!

I have this dilemma with my S&S build. I'm going for a 2 port junction box at the connection, and some extra cable, and the cable tie technique mentioned above. As I am planning the bike for ultra racing, I'm also going to stick an extra spare cable in my bag, along with the knowledge and understanding to be able to rewire externally if I need to.

J

[quixoticgeek]

This thread is the second time I have seem people advocate cutting a DI2 cable to allow fitting.  I would caution against this, the cable is of a construction that is similar to a silicon coated headphone cable so rejoining for a reliable connection is going to prove to be a very skilled job resulting in a joint which is probably larger than the cable end connector.  I would not trust such an unsupported (as in the cable not being attached to anything within the frame) joint on multiple 200km rides let alone a 1000km brevet (and I am quite handy at the soldering cables game!)

I'm an electronics geek. I solder surface mount components by hand, and even I would consider it crazy to try and split and rejoin a Di2 cable. You're just asking for trouble. Stick to using the connector units, sure it's expensive, but it's reliable.

J

[FifeingEejit]

When it comes to charging the Di2 a suitably beefy USB battery pack is able to charge it, didn't think it was possible while moving unless you go without gears but since I've got the bar mounted Junction A it's a bit trickier to hook up to the battery pack.

I thought you could charge it while you ride, but you lose the water proof integrity of the junction?

I've had a full charge from my PowerMonkey Explorer 2; it used about 10% of the battery capacity IIRC, which is less than my Wahoo takes (about 20%) and way less than the Lezyne Super GPS (about 60%) but since I've had about 1500km worth of gear changes with a mix of hilly and flat, and my tendency to use all available gears the chances of running out of gears during an Audax that doesn't involve more than 1hr charge time snoozing or sleeping seems minimal.
The challenge there is getting more power into the battery pack as it does need more than the Di2's 1hr...

The internal battery pack for Di2 is 3.7Wh. If you have a standard 3W dynamo hub, running into a USB-Werk unit, you can get approximately 2.5Wh for every hour of forward motion. Charging this into a battery pack to then put into the Di2, you can expect some loses, so better work on 2Wh per hour of motion, giving you 2 hours to put into the battery pack enough power to charge your Di2.

I'll need to hook it up and find out, I know it won't change gear while on the computer or incorrectly disconnected from the computer as I've made that mistake before!

Aye that's what I'm thinking, USB Werk into the PMEx2 which is claimed to be a 6000mAh unit, must have been more than a 10% usage though it wasn't from flat as it was at blinking green and I crapped out rather than it needing it.

Waiting for my SON dynamo hub wheel to be shipped just now, hopefully in time for BGB and a couple of test rides before then

[quixoticgeek]

I'll need to hook it up and find out, I know it won't change gear while on the computer or incorrectly disconnected from the computer as I've made that mistake before!

Aye that's what I'm thinking, USB Werk into the PMEx2 which is claimed to be a 6000mAh unit, must have been more than a 10% usage though it wasn't from flat as it was at blinking green and I crapped out rather than it needing it.

Waiting for my SON dynamo hub wheel to be shipped just now, hopefully in time for BGB and a couple of test rides before then

Your PMEx2 is 22Wh of power, so about 10 hours of cycling to fully charge from the USB-werk.

If you could test if charging while riding is possible, would be interested to know the status.

It still bugs me that you need a box of tricks to change USB power to shimano connector to charge the Di2. I understand that the box of tricks does more than just charge, but for when you don't care about that and just want charge functionality, would be nice if they made something simpler, or smaller, or just had a usb socket...

J

[billyam998]

interesting thread with a wide variety of views / responses, some good some less so. My two penneth worth :- I run ultegra Di2 on my Genesis Datum, it has compact 12-34 cassette, this proves ample for most things but was defeated a couple of weeks ago by a couple of the climbs on the Knock ventoux. obviously the gearing would alter on the moulton but, I'm pretty sure there must be chainrings to suit.  With regards the battery, it is internally mounted in the seatpost, I have never experienced any issues with it running out of power on a ride - even so I carry the charger and, a power pack just in case.  After the LEL - which I did not connect the bike to a charge once, the battery showed as still having 60% power on the etube app. Even after last weekends london orbital - a total shift fest of short sharp hills,  which I ece'd out and, back to make it just under 600km for the weekend, the battery showed at 85% when I got home. I had a bit of  a mishap with the first battery which I broke when I removed it from the seatube rubber, it is quite amazing how little is inside the casing, the actual battery is the size of a single AA, which really amazes me how long it lasts for.

[grams]

My setup shifts fine while charging.

re: splicing: A Di2 cable is two cores of ordinary stranded wire, nothing like the horrible enamelled mess you get inside a headphone cable. A bit of heat shrink will provide plenty of support.

[Brucey]

I don't think a spliced joint in the cable should be a show-stopper; it just needs to be waterproofed and mounted in such a way as it isn't flapping about. Just like any other connection really.

If you want to retain the separable nature of the moulton, you either need to make the cables etc QD from the handlebars, or use a plug and socket inline.

FWIW I wouldn't choose Di2 (or even STis come to that); the former is more complexity for little gain, and the latter effectively presupposes that you spend most of your time riding on the hoods, if the gear controls are to be 'handy'.  I don't think they are terribly ergonomic to use (and I never have done, even though I've owned bikes with them fitted for 25 years or more). A set of kelly's take offs (or suntour command shifters) or even shifters mounted beneath the tops suits me well enough, and are easier (require less force at a stupid angle) than STIs.

Obviously there is less chance of intractable roadside trauma with a simpler system fitted.

cheers

[FifeingEejit]

I'll need to hook it up and find out, I know it won't change gear while on the computer or incorrectly disconnected from the computer as I've made that mistake before!

Aye that's what I'm thinking, USB Werk into the PMEx2 which is claimed to be a 6000mAh unit, must have been more than a 10% usage though it wasn't from flat as it was at blinking green and I crapped out rather than it needing it.

Waiting for my SON dynamo hub wheel to be shipped just now, hopefully in time for BGB and a couple of test rides before then

Your PMEx2 is 22Wh of power, so about 10 hours of cycling to fully charge from the USB-werk.

If you could test if charging while riding is possible, would be interested to know the status.

It still bugs me that you need a box of tricks to change USB power to shimano connector to charge the Di2. I understand that the box of tricks does more than just charge, but for when you don't care about that and just want charge functionality, would be nice if they made something simpler, or smaller, or just had a usb socket...

J

Will need to run it down a bit before I can test; so probably Tuesday...

[zigzag]

i would use a standard and abundant 53/39 combination which imo gives a nice spread of gears for a non-racy 20" wheeled bike. it would also cause less (if any) chain rub due to bottom bracket flex.