fooferdoggie 

I don't know of our setup is normal since its s a e bike tandem. I thin kit is a 48t chainring. but since we have a couple more gears doing 20 mph having better hill climbing ability is more important. It would be easy to change the front chain ring but it has the smallest one Now side it has a gearbox the 15t front chain ring is about a 38t chainring. this is the info I have on the crankset Crankset: FSA 170 MM INTEGRATED CHAINGUARD/SHIMANO ALIVIO 26-36-48/175 MM

unikid

I agree you have a Shimano crankset but A) you don't have 3 chain rings and B) you don't have a front derailleur. Did you count all the teeth on both chainrings shown in the picture? How many does each one have?

Also you don't show any picture of your rear wheel. What kind of rear cassette do you have? How many gears and how many teeth do the largest and smallest cogs have?

Until we have all that information in hand it will be hard to give a complete recommendation.

fooferdoggie 

it has a 11-36 cassette. so thats a bit on the small side for the large cog. it may be easier to just get a new cassette. 10 gears I think the main chainring was 46 but I will have to count it to be sure I cant find any info on their size. we have more then enough top speed but I would like to be able to climb the 14 to 16 degree grades better. I don't know if we could manage 16 with the gearing we have. here is what we have on the drive train. I realized I could not change the chainrings or they wont really match in cadence so it has to be the cassette but that costs less and its easy to do. .

GEARING DETAILS:

10 Speed 1x11 Shimano Deore XT RDM-8000-GS Derailleur with Shadow+ One-Way Clutch

SHIFTER DETAILS:

Shimano SL-M8000 Triggers on Right (Two-Way High Lever, Four-Shift Low Lever)

CRANKS:

FSA CK-745 Alloy 170mm Length Crank Arms, 175mm Rear, 15 Tooth Chainring

Chris_W

Can you ask the shop where you bought it to advise you on what will fit on that rear crank? It's a Shimano (only your front crank is an FSA) with 104 mm BCD, 4 arms, but some of them have odd shapes on the spider's arms that mean that not all rings fit. Get something with 10-20% fewer teeth than now and it will make a noticeable difference.

As long as you only change the inner, drive chainring, your pedals should remain in sync and your cadence will continue to be matched.

As I said, if this is all too complex then visit your local shop.

fooferdoggie 

duhh only the inner. or the cassette. I bought it from the importer and he admits he is not much of a mechanic. he was selling them through my local e bike store but they just sat around. they are so busy its not practical too bring it in and my wife cant make the 20 mile round trip yet. my rear derailed may handle a 11-42 cassette thats a 55.00 fix. I could take it into a closer shop and ask either one would work. the bike climbs pretty well all said and done but the steeper stuff is pretty hard for my wife 14 to 16 degree grades are steeper then most roads. its a bosh based bike so its not hard to find someone that will work on it. I can do it if I knew it would work.Now if my wife behind could be as easily dialed in (G)

Artmo 

Fooferdog: the lowest gear you have with 48Tx36T=36” is pretty tall for a tandem, but presumably the turbo setting on the Bosch is designed to compensate for this. Normally a low tandem gear would be in the order of 30Tx36T=22.5”, so you are a long way off that. Even with a 46T front and 42T rear cog you would only get to about 30”. Still high.
Are you using turbo with lowest gear on your climbs? I don’t see how, with a single 48 or 46T chainring, you can get a very low tandem gear and a reasonably high one for the flats.
We have aShimano system on one of our tandems, with a hub gear, but I don’t know the gear inches. However, on the highest power setting and a combined ages of 160 we can manage 15% climbs with a struggle!

fooferdoggie 

I just checked after I bought a chainring and the one I bought and The one on it is 40t. with the Bosch motor it adds 300% to your effort so it does a lot but when you get into those really steep slopes it is not quite enough. my regular bike with the Bosch speed motor with the same torque it is work but not too bad. so maybe a 34 tchainring would be enough. I don't need a huge amount more. we don't hit those slopes all the time they are short ones. yes we are using turbo on those nasty slopes. 16 degree grade is about 26%

Artmo 

You will feel a big difference with a 34T, at 25.5”, but your top gear will be only 83”, so I hope you like spinning😊. Good luck!

fooferdoggie 

with the gearing I have now at 20 mph we still have two gears left. so it should be ok. we will test it and see. worse case another cassette. the motor kicks off at 20 mph and I don't think my wife likes to go too much faster.

fooferdoggie 

well after putting the 36' ring on and then putting the non ramped 40t ring back on we went out for a ride but I found the chains were touching in the last two cogs. the bike came with a flat inner ring and the outside was ramped and that as some offset to the outside. the nI put the ramped 36t ring on I put the smooth 40 on the outside to make it look nice nope. so I put the ramped 40t ring on the outside it seemed fine but there was a little rubbing under power on the last cog. so I need to get some washers to put behind the outside ring. but we get around 22 mph with this gearing and thats plenty. with work we got up a 14 % hill.

fooferdoggie 

well the washers took care of the chain problem. we hav at least 22 mph before spinning out so we are fine. I am going to look into a 11-42 cassette so those steep hills are fun not a struggle.

Leisesturm

Hokay Fooferdoggie, I finally have some time to address your concerns. Not that you haven't had some good help so far (you have) however I fear that you are still not providing an optimum experience for your Stoker and this tandem thing only works with an engaged and happy Stoker. I have taken a picture of my Stokers saddle from the angle that I would like to see your Stokers saddle from: above. See that notch in the back. Unless hers is that deep then she will have tailbone issues. Just because she is no longer complaining about it does not mean everything is fine. Some Stokers are stoic and will not complain until they suddenly just don't want to ride anymore.

Next. You might be doing a lot of damage to that motor by trying to ride up steep hills that you cannot manage. You have made changes to the bike that I don't quite understand. Maybe you can take new pictures that show what you have done. You were willing to swap the positions of the drive crank and the timing crank which tells me that you didn't really understand an earlier posters advice that the outside chainring on the Stoker crank MUST be the one that came with the bicycle. It has been chosen to match the one in your Captain crank. You should line up your pedals with your Stokers pedals. That way you always know where her feet are because they match yours. You put power out better. It's just a better way to do it.

fooferdoggie 

I ill get some pics as soon as the bike is back. It is ion the shop getting a 11-42 cassette added.
I spent extra to get an adjustable saddle so it lets me dial it in on width and gap. It is pretty close to great for her now.
I left the outer chanting the same but I had to put some washers behind it to keep the chains from touching when in the smallest cassette gears. They used a flat chain ring on the inside and a ramped on the outside to get enough distance. The only chainring I could find was a ramped one. But it works great now.
The crank arms cant be matched because the front chain ring freewheels she can pedal while my cranks are still. Thats a bit strange but unless the motor is on the back cranks the only way.
The Bosch motor is fine having lower gears helps it. Now we will have 36x42 as the smallest gear that should take a lot of stress off the system.

fooferdoggie 

Ok here are some pics. with the 36t chain ring 11-42 cassette and the seat I found my wife. I figured an adjustable seat would be good since it is hard to buy thing like that right now. we went up mount tabor here in portland it was all climbing and 12 % grade was about the max. no problem at all we did not even use the last two cogs. we went up a 14% grade on the way home still had a cog left and one power level left so we should be able to climb anything we need too.

Artmo 

Leisesturm: a slightly annoying feature(?) of the Bosch and Shimano tandem e-systems is the out of sync, because the captain can coast while the stoker is still pedaling. On our Circe Helios, I call out “sync” and we get into sync.
I don’t think the motor will suffer on a steep hill because it only responds to the amount of torque applied by the riders through the gears and is built for that.

fooferdoggie 

ya I would have to spend 8000 on a mustache brand tandem to get the motor in back \. I rode up up such a steep hill on my bulls bike with a Bosch motor it was so steep that even standing up with my 185 weight and full assist I could hardly get up it. but the bike will climb what we need now so it wont limit where we can go. only my wife motor or rear end will limit t (G)