Bettie 2.5: Bringing the Monkey Back


by Byron on Sep 16, 2008 at 9:01 AM

We just updated Bettie to 2.5 with the addition of the Stokemonkey – we did it with a one-time exclusive, Rolling Jackass mount and barrel-adjustable tensioner. Bettie 1.0 was stoked and when we built Bettie 2.0, we already had 2.5 planned. Our decision to make a Monkeymount was driven by back-to-school and getting the kids to and from schools. For those wondering, Stokemonkey status is best found on Clevercycle’s blog. At this time, according to the blog, they are not back on the market. We recommend Stokemonkey owners wait to hear from Clevercycles on the status of Big Dummy mounts and Stokemonkey retrofit kits.


I’ve written extensively about the Stokemonkey and Human Electric Hybrid Drive when we built Bettie 1.0. With 2.5, a Stokemonkey Nuvinci drivetrain is a pleasure to ride. It’s like a smooth, automatic transmission on a car. You’re applying power to a continuously variable planetary hub. That means there’s no gears and it’s quiet, almost effortless and efficient. It does take some skill – nudge the Nuvinci with power off, then back on and do it simultaneously to not jerk around

You’ve got to unthink how you shift now when riding Nuvinci and learn all over again. The twist-shift visual indicator is a good analogy. It looks like an inchworm and that’s how you should think about shifting. Instead of gears, it’s minor adjustments. You nudge it either easier or harder and maintain a continuous cadence.

That continuous cadence is key; especially with power on. Bettie 2.5 is equipped with a Rolling Jackass Custom chain tensioner so that dual chainrings can be used with the NuVinci hub. The small ring gets us up 17% grades and the Nuvinci, under load, requires you to pedal in circles. If you don’t, it’ll kick back against the chain. That’s magnified with the Stokemonkey and for the hills, I’ll stop applying pressure to the pedals from my legs and let the Stokemonkey and Nuvinci do their thing.

Here’s video of the drivetrain in action.

When Val fired the Bettie up, I said, "Electric MonkeyLove."

Damn it’s cool. And this morning, I took Kid 2 to school, up the big hills with power to spare. Next up is Kid 1 who HATES that I take her to school on a bike; especially when I honk the airhorn repeatedly and wear my euro gear.

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Surely by now somebody has come up with a stokemonkey style add on for Big Dummy and other longtails.

A robust aftermarket—please someone make an all-weather xTracycle bag, please—is good. Rolling Jackass is not going to make more. It took a day to machine that bad-boy, but I’d like to see them market that tensioner or another tensioner like it. You need an on-the-fly adjuster for the Stokemonkey, preferably with a big-ass dial.

Looking at that Stokemonkey I can’t help thinking that it looks like an orange ceiling fan on its side with a cog instead of blades. Hmm, this gives me a really bad idea.


I see where you’re going with that and yep—the Stokemonkey works because it’s part of the drivetrain, instead of a hub driving a wheel. There are advantages/disadvantages of course, but overall you can then toggle power as you need to when pedaling—when we first built up Bettie 1.0 with the Stokemoney, I joked that it was like having one of Lance’s legs with you. Over time, I’ve also got into the technique much more—feathering the power and then matching that to Nuvinci’s quirks.

Remarkably, I can get it to sound like a weird electric motorcycle. Accelerate, drop power to shift, re-accelerate, repeat all the way through the powerband—also sounds like that old [Rainer Beer commercial](

And by [staying on top of the gear](, I can really haul ass. Of course, that’ll blow the battery right out and I’ve learned that humans are programmed for speed. First thing you want with the Stokemonkey is more power.

The next-gen Stokemonkey I hope evolves with the electric motor power industry to lightweight, longer-range, fast-charging batteries.

I am considering a Rohloff for my BD and was wondering why you selected the Nuvinci?  Can you compare and contrast in for me?


We’ve building up *Barney* right now with a Rohloff. Barney is Bettie’s alter-ego, another approach. Nexus, Rohloff, Nuvinci are all good choices. Seattle Bike Supply partnered with us Bettie 2.5 and they distribue Nuvinci. As I wrote, it’s got it’s quirks, but no gears—a cvt—works mostly very well with this setup. The issues are the kickback, when using a second chainring with the Nuvinci and pedaling lots of torque on it.

@ Bigger Dummy -

We are building up a Barney 1.0 that will be in contrast to Bettie 2.5

Barney will feature a Rohloff. We hope to unveil Barney after Interbike is over. In the mean time, I’ve found quite a wealth of information about the Rohloff equipped Big Dummy experience here:

Enjoy! -Galen

  Compared to the NuVinci, the Rohloff has a wider range, is substantially lighter, and costs around three times as much.

  Compared to the Rohloff, the NuVinci is about 1/3 the price, weighs almost twice as much, and has a continuous range that is not as wide.

  In this case, the NuVinci was chosen for many reasons, particularly its ability to withstand extreme torque.  This makes it well suited for cargo bikes, especially when the electric assist is added.  The Rohloff is an extremely robust hub, but shifting under load with the added horsepower of the StokeMonkey involved could lead to problems, as it becomes far too easy to apply torque when the hub is not fully shifted into gear.  While it does take a bit of experience to learn to shift the NuVinci effectively, it is not possible to mis shift, as it is always in gear, and can take extreme torque at all times. The ability to fine tune the ratio can also allow the rider to maximize not only their own efficiency, but that of the StokeMonkey as well.

  For more impressions af another NuVinci equipped BD, look here:


Could I get some more info about your chain tensioner? I have SM #3 and I really want to get rid of the stock tensioner. It looks like you’ve got the replacement idea figured out.

Also, I believe that the new mounts are on the market now. Check with Todd and his blog.

I would also love to talk with anyone on a BD/SM in colder climes. I’m in Madison, WI and have been riding a Kona/SM/BD for almost 3 years. Plenty of stories to swap.

Go Monkees!

Michael:  That tensioner is made from 1/8” wire rope, with U-bolt style cable clamps to make loops.  A turnbuckle in the middle and a loop around the seatstay bridge of the Big Dummy (covered in plastic tubing to protect the paint), and Robert, as the Brits say, is your parent’s sibling.  Solid and simple.