Tandem Conversion

[Bill Cook]

Have recently built two ebikes (mountain) with Bafang 750 and 1,000w kits. Very elegant stuff!!
Here is the challenge: we have a 1993 Santana Noventa tandem (columbus tubing, fillet brazed) that we would like to keep in the family, but we have a newer Santana that we travel with. Why not try to electrify it and have an excuse not to sell?
Have checked online and looks like the conversions are pretty funky.
Any ideas?

[Felix D'Kat]

Hi Bill

Nice tandem you have there, in excellent condition for a 25 year old.

I'm a real newbie to the E-Bike scene but that looks like a real challenge
maybe look at hub drive rear wheel, I think you will run into some issues with the link chain between the 2 cranks

Cheers
Felix.

..

[ncmired]

You've probably come across this BBS02 tandem build video already, but if not, have a look at the chain clearance starting at about the 3:30 point - tight but doable, on this build anyway (not with a BBSHD though).

[Bill Cook]

Thanks for the video reference - had not seen it. Yeah, the chain clearance on timing side seems too tight. I have a spare BBS02 sitting around and may mock it up on the Santana next week.

Rough measurements outside of crank arms: BBS02 - 190mm, Santana - 140mm. Since will be using just one chainring should be OK if 50mm is on right (chainring) side.

Will let ya know. Thanks!

Bill

[iansmillie]

I'm about to do a tandem myself, but on a 1979 Schwinn. I think with the length that mid drive is the way to go.
The bike is about 60 pounds, add 2 riders and you get 350+ pounds to push makes a 1000W drive a likely choice.
It's an old Chicago steel Schwinn so it should be able to handle it.


If anyone has heard of one of those being done, or some sage advice, I'd love to hear it.

Ian

[Bill Cook]

Hi, Ian...
Think you may have clearance issues with the chainrings on right side. The BBSXX has one sprocket on right and I don't know how you are going to make the timing chain work. I'm midway thru installing a BBS02 on the Santana (timing on left side) and have had to file down inside of stoker timing sprockets for clearance - no big deal just a lot of fitting. The BBSHD is way too wide for installation on this tandem.

[Bill Cook]

Finished the Santana build. Pretty easy although I had to do a lot of filing on stoker timing chainring - still 100% functional. Used a BBS02 as the BBSHD is way too wide. Bike weight is 56 pounds (with battery). Not too bad for a steel tandem! See attached photos.

[Jsshort2302]

Hi Bill, great job on this install. I am thinking of the same but I want to install the motor up front, no chain ring on the right side of the motor, but instead, install the normal left side drive crank to the sq taper BB. My concern is if there is clearance for that. The second concern is the fabrication of a chain tensioner for the timing chain but that is easy if there is clearance for concern number 1. I just want to keep all the gears we have with the triple crank and 9 speed cassette. I read on the California e-bike site that the two set screws will be in the way of the motor install but that doesn't even seem to be an issue if installing from right to left. I do see that it would make the eccentric virtually unusable, hence the fabricated chain tensioner.

[Apeekachu]

I finally completed my tandem build with a bbshd. I had to move the chainline from captain to stoker from left to right side because the stoker left chainring would not clear the bbshd. Chainline alignment was another issue but was solved cutting off the square taper axle of my old bb and welding it onto a new 127.5mm shimano bb. Surprisingly the alignment is near perfect. This is a budget alternative to purchasing a 145mm phil wood bb but also likely more prone to failure unless its professionally welded. I welded it myself, can't u tell from the craftmanship haha? It's been a blast to ride even without the stoker.

[frankboy3]

Apee,
By having the drive and timing chain on the right side, can you just use the mid-drive without pedaling?

[Bill Cook]

Hi Apee....

Interesting. Can you describe the setup on stoker drive side? Looks really cool with the red chainrings. How did you attach to the Bafang chainring?

A side note: I was so proud of the Santana build and took my wife out last weekend.......She nixed the idea saying that as she hates hills (we're in San Jose/Cambria) and with the electric assist she wouldn't be getting the workout.

I switched out the stuff (about 1.5 hours) and we're back to stock. Hiding the BBS02 in wine cellar in case she changes her mind - maybe the HD if your drive side arrangement works and she relents. We have another tandem that we mostly ride. Lots of folks in Cambria want to buy the BBS02 kit.

[Apeekachu]

Hi Bill,
Any square taper crankset with a single chain ring can fit on the drive side of the BBSHD. Mine is the stock Truvativ 5D that came on the tandem. I forget if it was originally a triple or double crankset. I didnt use any of the BB spacers provided with the kit.

As you can see in the pics, having the drive side on the right side, the outer ring is pushed out fairly far therefore the reason why I had to extend the captain's BB axle. The alignment is near perfect using an 8-speed chain.

I'm currently running a 42t Lekkie bling ring (inner) and the outer is 38t as well as the captain. Paired up to the existing 11-32t 10-speed cassette, I've been able to top out at 36mph on the 11t cog riding solo.

[frankboy3]

Hi Apee,
First of all, great job your bike looks awesome! BTW, I have that same Trek tandem bike that I would like to convert and I didn't think it was possible to add a mid-drive system until now—thank you.

I would love to get your conversion parts list from you so I can duplicate your setup. What size battery are you running? Is it possible to use a frame mount battery with this setup? Is there anything you woud do different or fix? The rear brake and deraileur cables runs under the frame so how did you handle that? -Frankboy3

[calfee20]

Hi Bill,
Any square taper crankset with a single chain ring can fit on the drive side of the BBSHD. Mine is the stock Truvativ 5D that came on the tandem. I forget if it was originally a triple or double crankset. I didnt use any of the BB spacers provided with the kit.

As you can see in the pics, having the drive side on the right side, the outer ring is pushed out fairly far therefore the reason why I had to extend the captain's BB axle. The alignment is near perfect using an 8-speed chain.

I'm currently running a 42t Lekkie bling ring (inner) and the outer is 38t as well as the captain. Paired up to the existing 11-32t 10-speed cassette, I've been able to top out at 36mph on the 11t cog riding solo.

Why didn't you put the connecting chain rings on the left side to equalize the pedal offset, and you could have avoided that weld job.

Oh I see the motor is in the way...........I have on my first bike a 100mm BBSHD on a 66 mm BB so I had to machine a sizable spacer to fit it on. The amount of stick out I have may be enough to get the connector sprockets over on the left. You would have to get a different BB for the front however. Maybe one of those Cyclone BBs

[Cangaceiro]

Hi Guys,

Firstly big thanks to Bill and Apeekachu for the instructions on how to they converted their tandems, I would not have tried this without the information they had shared.

I have hills in my area and my passenger is not always unable to peddle, so I wanted a mid drive conversion instead of hub motor.

The bike I converted was a cannondale tandem, using BBSHD.

The cable bracket holder under the stoker BB I removed to fit the mid drive.



Mid drive size I used was the one for BBSHD 68mm BB size (not the larger BB sizes). It fit OK without spacers.



Once installed, with cranks back on, there is not enough room for stoker chain ring, as BBSHD sticks out too far on the stoker chain ring side.

I flipped the chain ring so chains run on the right side as per Apeekachu. Brilliant idea mate !

I used the Lekkie 36T chain ring on the mid drive. I think the offset is 5mm. The Lekkie 42T offset I think is 18mm, so if you end up using 42T, your chain alignment from mid drive to cassette will be better than what I have. I'm using it, but if I could do it again, I'd go 42T for better alignment and change my rear cassette to a wider range. I'll probably do this as it wears out.



For the stoker to captain chain alignment, I found this part from Lekkie which is a square taper extender. It extends the bottom bracket without having to weld anything on to the BB.

This was the part of the build I had the most difficulty assessing (finding someone to weld the BB extension for me). Instead of welding, once you have this part, it just taps on and your build continues. I've had no issues with it strength wise.

https://lekkie.tech/product/lekkie-square-drive-axle-extender/



Captain bottom bracket square taper with extension, on the side that has been flipped.



Alignment below with the square taper extender fitted on captain BB to stoker mid drive.



Tandem.

[smokiescfi]

That is an awesome build Cangaceiro. I've converted a Specialized Rockhopper with a BBSHD. I have a Cannondale MT800 I want to do your build to. What crank arm/chain ring did you use? I assume it was the stock Cannondale. I will go with the 42 tootk Lekkie like you suggest. How were you able to run the cable for the rear derailleur?