I agree that the unusual chainring difference is the culprit. The vast majority of road bikes use 50-34 or 53-39 chainrings for good reasons: good gear range and reliable shifting. A 19T gap is problematic for Di2 but shifting will be much worse if the team goes back to a mechanical drivetrain. I use both drivetrains and Di2 is clearly superior when installed properly.

The easiest solution is to replace the 53T ring with a 50T. He may miss the occasional "ego boost" on downhills but the overall ride will be much more fun.

Akexpress called me & discussed my situation. Aside from my shifting incorrectly, the likely biggest problem is the 53/34 difference. I will likely get a 50t big ring.

So, if we are willing to give up a high top end and I can train my brain to shift properly, I can likely make this work.

Thanks for all the experience & advice.

Also with a 50 on the front and 11-36 cassette you can basically ride it on the big chainring most of the time and only use the 34 for climbing proper hills. Then you won't be needing to use the small-small cross chain combinations.
It is worth persevering with the Di2. Sure you can trim you 8sp to perfection but with the Di2 set up properly it will be right all the time with no trimming required.

Again -

Right now we are 53/34 up front and 11/36 in the rear. We also have a K-Edge derailleur cage. AKExpress recommends Praxis chainrings. I have looked online & they have great reviews.

Another option might be to change the front out to 52/36 (16 tooth difference) and go to an 11x40 in the rear. This would allow us nearly the same top end but still be below 1:1 at the low end.

Would this be problematic?

My opinion is drop some of the top end, unless you are a team of national class racers. Maybe go to a triple 26 on bottom? 48 on top. Then you can get a tighter cassette. For the adreniline rush you can still hit 40+ mph. But at my age it's more scary than fun.

I would drop the top end and learn to spin more. We have the 50-34 with 11-32 and can get well over 40mph. My stoker is not happy at that speed so it's enough for us. We swap out to an 11-36 with the Roadlink adapter for the "mountain" rides.

I've seen other posts here that the 40 tooth cog works fine with the K-Edge conversion but you will be getting bigger jumps in your gears.

I guess that we're used to big jumps - just not "huge" ones (53t - 34t). We may have to give up some top end.

However one of the things that makes me feel like Superman (briefly) is when we close in on a much younger, stronger rider near the crest of a hill, gradually upshift until we hit the 54/11 and watch him try to hang on as we pedal up to 45mph. This doesn't happen often but it is a real ego boost when we get the opportunity. I'd like to think it makes them appreciate what a tandem can do. It puts a smile on my face when we can do this. It is one of the things that sets tandems apart.

Yeah we have a 50T big ring and an 11-34T cassette which gives us all we need for our flatish bunch ride in Group 2. 10sp cassette so the jumps are good. We never get off the big ring in that bunch and don't spin out on the run-in to the cafe @ 55kph if there is a tailwind and we are fit. We are both happy at 105+ RPM, bursts up to 120RPM no problem.

I know what you mean, it is a buzz! Our bunch riding friends are learning not to overtake us near the top of climbs because we need room to get around them on the downs.

Just cranking it out and riding away from the bunch at the end as well is v cool.

I am still in the process of sorting this out.

Another question - not tandem specific:

In order to prevent or reduce the occurance of the chain rubbing on the inboard face of the big ring (when the chain is on the small ring) what would happen if one added some thin (say 0.5mm) shims to move the big ring further outboard or the small ring farther inboard? Will this mess something else up entirely? Is the offset from the small ring to the big ring a fixed number? Will this make shifting harder?

This won't work especially with Di2 and 11 speed. I don't think it would work with mechanical either . You will drop the chain in between on most shifts. The spacing is precise for the chain width. I helped with a di2 Santana that kept dropping the chain between the chainring a and it baffled us for a while till we figured out the shop mounted the inner ring backwards. Remounted it and it never skipped a beat again.

You need to keep the spacing between the chainrings the same. You can increase the chainline by moving spacers on the bottom bracket to the drive side if you can, or add chainring spacers to BOTH chainrings to move them more outboard.

oldacura - Wish I could offer some advice but I am certain that others here are more qualified, based on their experience with the Di2, of which I have none. My only comment is an observation to trust the builder. My builder saved me from myself when i spec'd a drive train that was popular on tandems - CoMotion, Santana, etc . - at the time but he said in his experience it did not shift well. Months later I read multiple reports of the problems shifting the system that I had asked for.

Di2 looks very cool and it seems many are happy with it but a good old Ultegra mechanical system has been adequate for me.

+1. You rarely benefit from it, and when you can, its rare that it lasts very long.

When I first bought my wife her smart phone, she hated it. Too complicated. After learning how to use it, she is now hooked. The flip phone still works, but the new one is so much better. You just have to learn to use it.

It wasn't the builder it was the dealer who steered him away from di2 then put on the system way out of spec. You can ride it that way for sure but at least tell the customer of the limitations and noises he is going to experience . Calfee and paketa and land shark have been innovative with di2 and tandems to everyone's benefit. Calfee had a seat post battery before Shimano in fact. It is a better mouse trap.

Finally got out this weekend for our 2nd ride. A correction: I stated earlier that our chainrings were 53t x 34t. This is incorrect. They are 52t x 34t.

I updated the software on the Di2. I increased the display time on the gear/battery display from 5 seconds to 120 seconds. This makes the display more useful.

Based on recommendations here our recent ride went significantly better. The two suggestions I tried were: ride mostly on the big ring. Use the small ring only for climbing hills we can't handle with the 52t x 36t combo. This helped significantly. I was able to concentrate on shifting the rear derailleur only. The other suggestions was to try to train my brain to shift correctly. Someone's suggestion to use the mnemonic device "smooth is smaller" helped me shift the right direction. I mis-shifted only about 10% of the time (instead of 50%).

These two things permitted us to enjoy the ride much more. What we were able to appreciate more was how smooth the ride was compared to our old steel bike.

I'd say the main complaint I still have is the big jump from the big ring to the small (52t to 34t). This is a huge drop. I would have to think quite a while to try to plan this shift & still did not pull it off well. One way that I think I can improve this is to call out to my stoker "downshift" so she knows our cadence is about to spike and maybe able to ease up on the torque a bit. If I can figure out a way to upshift the rear a bit at the same time that I'm downshifting the front, this may smooth the process considerably. I have read that "Synchroshift" is available for the XTR version of Di2 - but not for the road versions. Is this true? If so, does anyone know why? I would think this would be a feature that could significantly smooth out the shifting process.

Also, based on recommendations from AKExpress, I have ordered new chainring sets from Praxis: I got one set at 52tx36t and one set at 50tx34t. In one case we would give up a bit of bottom end & the other would give up a bit of top end. I have not yet installed either.

However, even with our ring span within the Shimano recommendation of 16t max, I think it will still be a big jump from big to small (or the reverse). Have others here developed a technique to make this jump smoother? Our old bike was a 54t - 44t jump. I had become accustomed to this smaller jump.

Thanks again for all of your experience & help.

There are several reasons why "Syncroshift" is not available on Di2. With 2 vs 3 chainrings, it's harder for Di2 to get into a bad gear combo. For road racing, there's also a tactical advantage to shift the front and rear gear independently (ie. w/o Synchroshift). For instance, I may shift to my big ring (w significant gear jump) to launch an attack or to bridge a gap. For mtn biking (racing or not), it's more important to be in the right gear because the terrain can change abruptly. For example, a steep descent may be followed by a steep climb with sketchy traction. Using the right gear in split seconds can mean the difference between walking or staying with the pack.

I agree with AKexpress' suggestion to try the 52-36 and 50-34 combos. They're popular for good reasons.

When we shift from 50 to 34, I will say "small ring" to my partner and she'll ease up. Depending on the terrain, I may also shift to a harder rear cog at the same time to make a smoother transition. BTW, one minor drawback to SRAM eTap is that it can't shift the front and rear gear simultaneously.

I did read an online article on the Fairwheels website about the issues with doing synchroshift on a road Di2. Not sure that I agree but I do think that Shimano is conservative in this decision and would do it if they could stand behind it.

If I can get in the habit of calling "downshift" can I ease the big jump by simultaneously hitting the downshift (rear) button on the left and the upshift (rear) button on the right? Should I maybe do one tap on the left & 2 or 3 taps on the right? I have not changed the traditional (default) assignment of the shift buttons.

On this weekend's ride I did try to get in the habit of calling "downshift" to my stoker when I was about to drop from the big ring to the small. This seemed to help a lot. She could anticipate that the resistance was about to drop and the cadence would spike. In conjunction with this, I tried shifting both the front down & the rear up at the same time. This seemed to help as well. I think that when we dropped from the big ring I would drop one or two gears smaller in the rear.

I also tried to drop from the big ring to the small before I got to big-big. In anticipation of the need for a lower gear, I would drop from the big ring and at the same time try to drop to a smaller cog or two in the rear.

After more experience with Di2, I am beginning to like it more. When I switch from my Dura Ace STI mechanically shifted single to the Di2 tandem, I can see that the Di2 shifts faster. However, I think that our older bar-end shifted tandem shifts as fast & surely as the Di2 - especially on the rear. The Di2 may be a solution for STI but not really "better" than bar-end shifters.

So I may be getting away from the wish for a Di2 triple. However, I'm thinking sychro-shift may be pretty nice for road shifting. Is this just a hope or is it likely in the near future? Is there something inherently more difficult in this than for XTR or have they just not rolled it out yet? Is it possible that this could just be a software upgrade?

I think that I mentioned this before but it is worth mentioning again. When I shift from the 52 to the 39 I up shift at least 2 gears on the rear and then shift the front. I tell my stoker what I am doing and we do not have that abrupt spin up. In your situation you may want to up shift 3 gears.

Egads! Now I'm even happier I retrograded all my bikes, single and tandem, back to bar-end friction shifting with Suntour VGT derailleurs. Got sick and tired of flimsy brifters, bad shifts, hopping chains etc. Maybe I'm incompetent but maybe that is enough to have something easy and durable. Reprogramming shifters??!! No thanks. Also, had an exchange with Adventure Cycling over their Big Shift article where on product manager quoted implied knowledgeable riders go 1x and ignorant, inexperienced riders go 3x. To me, if electronic means 2x, forget it. No matter what range you can get 2x, I can get more 3x or for the same range, I can get closer gaps. I may be in the middle ring 90% of the time but wouldn't give up the other two. Why? For a few oz? I don't race so they don't matter. Nice to have the extra rings when you need them, tandem or single.

Respectful rants are always a fun read. While I don't have a problem with folks wanting to ride their e-bikes, I myself started with a steel bike equipped with 1/2-step crossover gearing and a deep granny gear all shifted with cable fed bar ends and later with thumb shifters on upright bars when the spine began to lose it flexibility. Just never felt the urge to go beyond nor could I get over the cost hump of that new fangled e-stuff.