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Tandem Cycling A bicycle built for two. Want to find out more about this wonderful world of tandems? Check out this forum to talk with other tandem enthusiasts. Captains and stokers welcome!

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Old 10-10-12, 11:05 PM   #1
zonatandem
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Update: Test Dummies . . . Again?!

Updating on testing of Di-2 with NMH battery in stoker seatpost.
Asides from a couple minor issues listed in our previous post, at just over 1,000-mile mark, had to fine tune rear shifting a tad.
At 1,325 miles, the green little LED light by handlebars started flashing every so often when shifting, indicating battery life was going down.
At mile 1,360 our front derailleur ceased working, but rear worked fine; indicating it's time to re-charge pretty quick!
According to the manual a red blinking LED light was supposed to activate before that, but that did not happen.
Guess that's why we refer those those little LEDs as 'idiot' lights!
Hooked up charge unit to the little 'tail' under stoker's saddle for 3.5 hours.
Checked battery with voltage meter and decided to keep trickle charge going for another 3.5 hours to top off the battery.
So far so good . . . and we are still very pleased with the performance of the Di-2 unit.
Pedal on TWOgether!
Rudy and Kay/zonatandem
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Old 10-15-12, 03:06 PM   #2
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Rudyy,

I have a couple of questions regarding your test. How often have you had to charge the system?

Prior to using the Di-2, you were using a triple front deraileur, correct? Regarding the change to a double chainring, do you find that you require a lot more frequent shifts of the front chainrings? Maybe with the smooth shifting, this is not much of a problem?

Thanks!
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Old 10-15-12, 03:55 PM   #3
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What is the rear derailleur? Di-2 with a long cage added? How is it made to clear a wide range cassette as I would of thought anything bigger than a 30t low gear would hit the top pulley?
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Old 10-30-12, 06:06 PM   #4
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colo tandem:
Recharged battery only once, at 1,360 miles.
No big adjustment for us going from triple to double chainring.
With the double (48/32) and 10 speed cog (11/34 cassette), we have 19 very usable gear combinations.
With the old triple/9speed cassette had about 22 usable gear combos. Our highest gear used to be 130 now is 120. At our age we no longer 'bomb' down the hils so if we spin out 120-inch gear, we coast!
Our granny gear is still mid-20s.
We spend most of the time on big chainring and the 32T is used for steeper/longer ascents.

Dean V:
Our builder, Bob Davis, installed a Yumea long cage on the Di-2 Dura Ace rear derailleur.
Works fine.
So far these test dummies are enjoying the ride TWOgether!
Pedal on!
Rudy and Kay/zonatandem
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Old 10-30-12, 07:42 PM   #5
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Wasn't aware till recently that the battery for those systems lasts for such a very long time. Would be a deal-killer if frequent battery charge/change were required.
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Old 10-30-12, 11:26 PM   #6
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The other advantage of the battery system is that it is located ^inside^ stoker Kay's seatpost and is not the same battery used by Shimano.
Pedal on!
Rudy and Kay/zonatandem
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Old 10-31-12, 12:41 AM   #7
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Wasn't aware till recently that the battery for those systems lasts for such a very long time. Would be a deal-killer if frequent battery charge/change were required.
I believe the standard Shimano battery is offically rated for 1000 miles (1600 km) per charge, but I've heard of people getting up to 3000 miles (5000 km) per charge! Charging frequency mainly depends on shifting style and air temperature.

In fact, the capacity is so good that there are several weight weenies who would like Shimano to release a race-day battery that is less than half the weight, but only has the capacity for a couple hundred miles or so.
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Old 10-31-12, 11:36 AM   #8
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Newbie-ish question here:

The one thing that concerns me about electronic shifting is dealing with failures 'in the sticks'... Aside from the battery dying, where the obvious solution is to carry a spare, if the circuitry itself fails, are you stuck? How would you deal with that?

I suppose that's not much different then some catastrophic cable failure on a mechanical system, but I'd like to hear how people plan for this (if they do...).

thanks!
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Old 10-31-12, 02:41 PM   #9
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Originally Posted by Esteban58 View Post
Newbie-ish question here:

The one thing that concerns me about electronic shifting is dealing with failures 'in the sticks'... Aside from the battery dying, where the obvious solution is to carry a spare, if the circuitry itself fails, are you stuck? How would you deal with that?

I suppose that's not much different then some catastrophic cable failure on a mechanical system, but I'd like to hear how people plan for this (if they do...).

thanks!
I deal with it by carrying one spare derailleur cable and one brake cable. I suppose for Di2 I should be a spare wiring harness? battery? Our tandem has no following car, sometimes goes where there is no cell service, and there is no one at home to call anyway (she is on the back of the tandem). Of course there are friends and relatives, only a few of which have an appropriate vehicle, but I have an aversion to making them take hours out of their day to bail us out of a bike maintenance issue.
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Old 10-31-12, 04:23 PM   #10
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Failures of any type of component can be a hassle and usually not expected!
Have had a chain jam/bend at the north rim of the Grand Canyon; nearest bike shop 300 miles away. Took me about a half hour of to fix it with mini-pliers and small screw driver.
Have broken front der. on 100 mile ride and then rear cable snapped later in the ride; yup, managed to finish.
Have ripped out half dozen rear spokes with unexplained overshift. Fortunately were within driving distance from home. Hitched hiked a ride home while stoker stayed with tandem. Got our car and picked up stoker/tandem.
For the Di-2 setup we carry no spares; keep tabs on battery by doing a voltage check before each ride with voltage meter.
If Di-2 fails totally (like no power/broken circuitry), you are stuck in the last gear you selected.
However you do get a warning/flashing light to tell you if battery is 'low.' If you don't pay attention to that, then front der. quits functioning but back is still good for a few dozen shifts.
Battery strength/life is dependent on how many shifts and even temperature.
Tested our battery up to 140 degrees Fahrenheit and still functioned; that was parked in the sun at mid-day/ summer in Phoenix for several hours.
Don 't know how well it holds up in freezing temps and no plan to test that!
We tend not to overworry about failures . . . deal with things as they happen.
On multi-day tours we used to carry spare brake/der. cable + folding tire + 2 spare tubes.
Oh, we don't carry a cellphone . . .
After 37+ years of tandeming we have survived all sorts of minor-to-major dilemmas.
Just our experience.
Pedal on TWOgether!
Rudy and Kay/zonatandem
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Old 10-31-12, 06:30 PM   #11
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I have had the local battery specialty store make battery packs for my riding lights, why have racers not had similar done for race day battery packs. Also, could you build a solar charger that was less weight and use an even smaller battery?
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Old 10-31-12, 08:33 PM   #12
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I have had the local battery specialty store make battery packs for my riding lights, why have racers not had similar done for race day battery packs. Also, could you build a solar charger that was less weight and use an even smaller battery?
I'm sure you could do this, but you'd have to check the charge generated vs. weight trade off. Solar panels are certainly getting better / lighter - you could probably get something that mounted over the top of panniers or a rack (but would you have a rack if you were worried about weight)?

Then some circuitry to feed the generated electricity to the battery - on a sunny enough day you might be able to get away with a ridiculously light battery.

Di2 battery weight is 70 g, so that's not much to begin with.

Also, thanks all for the replies to my question. This isn't an issue with our current tandem ('80 peugeot), just a consideration for the future.

Last edited by Esteban58; 10-31-12 at 08:37 PM.
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