Tandem Rans BBSO2 Build

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BikeFiver   1 mW

1 mW
Posts: 13
Joined: Jan 22 2014 9:23pm

Tandem Rans BBSO2 Build

Post by BikeFiver » Feb 22 2016 11:24pm

I like to ride recumbents and my wife will only ride tandem. The solution was to buy HER a Rans Screamer Tandem for Mother's Day!
Screamer R Start.jpg
Screamer R Start.jpg (58.94 KiB) Viewed 1111 times
Now to make it really fun... electrify it. We have been really pleased with our Rans Screamer (now named Green Lightning) with BBSO2 750 W.
GreenLightening R.jpg
GreenLightening R.jpg (56.59 KiB) Viewed 1111 times
We have found the power to be plenty. We use the 2 power level when in the 5 power setting. We only use the PAS never the throttle. We cruise level at 20-24 mph and any downhill is 25-29 in 54x11 gear. Max so far 38mph. We have a 50 mile range using 80% of the 17A/hr 50volt Em3ev battery. I think it was sold as 16.5A/hr but tested at 17.5 by EM3EV. Thanks Paul!
Dropout R.jpg
Dropout R.jpg (73.28 KiB) Viewed 1111 times
This is a key component. The rear wheel needed extra support to keep it in the dropouts. I machined these for both sides. Two peddlers and BBSO2 is way to much on quick release to hold. I know because the maiden voyage was interrupted by having to reseat the wheel 4 times.
Battery Box.jpg
Battery Box.jpg (74.85 KiB) Viewed 1111 times
This is where the battery rides. The right side is fixed to the bike, the left unbolts to remove the battery. Paul fixed me up with the 6ft of power cord to go from the BBSO2 to here. EM3EV will get my business because of that kind of support. I also bought some extensions for the brake and monitor leads just in case.
Bottom Bracket.jpg
Bottom Bracket.jpg (82.47 KiB) Viewed 1111 times
Here's where the neat part happens. Because this is a tandem, the stokers BB has the derailleur and is not effected by the BBSO2 replacement. You add an outside, slightly smaller 52 chainring with racing triple bolts and you move your drive line to the right side. Thanks for the info Harris Cycles. The bolts are getting hard to find but they are out there. I initially used the optional 52 t BBSO2 chainring but I have just changed to a Drop Stop 52t front chainring with 130 adapter (California Ebikes) to the BBSO2 as I was occasionally throwing a chain. I can't tell if it is thrown from the front or rear chainring. We will see if this helps.

Why is this neat? The captain can ease/freewheel the BBSO2 after tapping the brake to kill the power, shift while under peddle or stoker power only, and use all the normal 24 gear range. 54x11 to 24x34 on this bike. Great efficiency and no loss of top or granny gear. If you don't have electric power you must have granny gears for any tough hills as there is NO STANDING up hills with a recumbent bike. Just sit and spin!

This Screamer makes this chain drive line switch easy as the chain idlers are ambidextrous and mount to either side. It should be just as easy on a delta frame as there are no idlers to worry about.

Some have concerns about the stoker being locked in to rotating with the motor/captain as there is no freewheel at the stoker crank. My wife always has been locked in to my peddle cadence and I never use the throttle. This is one of the skills that captains and stokers work out on any tandem, powered or not. A tandem bike is a great way to improve communication in a marriage or hasten a divorce. I always call out shifts up or down as well as any bumps in the road. She watches the mirrors for cars, points out things of interest and navigates.

We have found the 750 watts to be plenty of power. We feel any speed above 27mph to become annoying for sustained periods due to wind noise and buffeting as well as the hyper attention to road required to avoid debris and holes.

We have 600 miles on this setup so far and it works great.

Thanks to all on this forum for the info provided for the build!


TheRammer   1 µW

1 µW
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Joined: Aug 12 2016 12:55pm

Re: Tandem Rans BBSO2 Build

Post by TheRammer » Jul 13 2018 8:32am


Thank you for the excellent description and photos. I have been considering something similar.

It is more than two years later since your build. How about an update? Everything still running well? Anything you would change?


BikeFiver   1 mW

1 mW
Posts: 13
Joined: Jan 22 2014 9:23pm

Re: Tandem Rans BBSO2 Build

Post by BikeFiver » Jul 20 2018 5:41pm

Rammer, Green Lightning has been a wonderful bike. I have made a few improvements to the design. I found that the older stock front idler was not up to the tension placed on the chain. I think Rans found this out as all the new Screamers now likewise use the Terracycle idlers as shown.
Chain Idler Front copy.jpg
Chain Idler rear copy.jpg
I have also found that the large 54 chainring is not needed as the 46 middle chain ring gives 28 mph at our max cadience. This has allowed the elimination of large ring in favor of more room for outside idler ring to decrease chain interference and give a more solid mount. I also replaced the standard 52 idler for another Wolf Tooth Drop Stop ring.
Chainrings copy.jpg
Here you'll see the entire package with the updated wheels, Terracycle idlers and handlebars, 2 Drop Stop chainrings and new rear rack to lower the storage via panniers and 2 high mounted daylight bright blinky lights. Note we have kept the granny gear even though we don't use it on our rolling hills here.
GL Right Profile1jpg.jpg
GL Right Profile1jpg.jpg (93.04 KiB) Viewed 821 times
My wife and I love this ride! Quiet, smooth, reliable. I do now use the throttle when launching from a standstill as this allows a motorcycle start with feet down and out of the clips to improve stablity and manage any low speed wobbles.
BTW the wheel changes were made to update the bike to give more durablity than the more racy stock wheels. I had the fine people at Velocity build up a set of Phil Wood hubs into their Velocity Cliffhanger MTB rims capped with Marathon Plus 20 and 26 x1.75.

kentruda@sbcglobal.net   1 µW

1 µW
Posts: 1
Joined: Oct 02 2018 3:08pm

Re: Tandem Rans BBSO2 Build

Post by kentruda@sbcglobal.net » Oct 02 2018 3:13pm

Do you still have the Screamer? How did you flip the front cranks so that you have the chainring on the right and still have the pedals facing correctly? I want to electrify my screamer and am trying to choose between the Bafang like yours or a Falco electric hub which is quite expensive. Thanks!

Warren   100 kW

100 kW
Posts: 1400
Joined: Oct 05 2010 11:35am

Re: Tandem Rans BBSO2 Build

Post by Warren » Oct 02 2018 11:47pm

He didn't flip them. He replaced them with the mid-drive unit, which has its own cranks. I assume he used the captain's left crank on the stoker's crankset.

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