Big Dummy Gets Smarter

Checked in with Surly Bikes yesterday on the Big Dummy and learned from Dave Gray, the Product Design and Development dude, that new factory samples are en route. Those samples should address much of our concerns with Bettie

  • Stand-over height
  • Rohloff’able
  • Whippiness
  • Disc brake compatibility

In my long-term Bettie notes, I’d complained about the stand-over height and whippiness as the two biggest issues. Cargo bikes should drop the top-tube right to the bottom bracket so you can easily step into and out of the bike, especially with a load or kids or both: the latest Big Dummy uses the Instigator’s top-tube design. The whippiness is an obvious problem and inherent to trailers whether attached or not. Any longtail should make that better, and Surly is making it stiff.

Rohloff is a good option, to simplify the drive train. Nuvinci is another.

The disc brake problem came up for us because we’re using Magura’s Gustav for the stopping power on really hilly routes, fully loaded. The Gustav’s need exact tolerances and the Xtracycle just didn’t have them, even after using Magura’s planing tool.

It was great talking to Dave and hearing about the Big Dummy.



7 Comments

word on the top tube. that bites me all the time, especially with the peapod seat attached. as far as the rohloff goes, how is it with loads? i noticed with my nexus 7-speed if the bike was loaded, the hub seemed “abused.” hence my eventual gary fisher / free radical combo.

man i can’t wait for the dummy. i’m ordering as soon as they give the word.

My understanding is that Bettie is built as a 29er but the Big Dummy will use 26” wheels.  That presumably helps with the standover height, but do you think that the larger wheels help with rolling over bumps and curbs with less disruption to your load?

Brian,

That’s my concern exactly on the Rohloff, but considering how that’s built it may very well handle the load. I don’t know yet if we’ll build it with the Rohloff, but it’s a candidate. We’re also concerned about Todd’s pausing the sales of Stokemonkey and where that leaves us. We may very well build Bettie 2.0 without the Stokemonkey, but opt for a new drivetrain.


Martin,

Bettie is built with 26 and the Big Apples, which is about a 29er. That presumption is incorrect—well we thought so at the time It does help with toe/foot down when stopping and starting but the standover is still to high with that top-tube. And we wouldn’t have really known that until we started carrying big loads on Bettie.

As a design study, we’re learning a lot with Bettie—as a stoked xTracycle it’s outstanding. Where we need to refine it is in the cargo function and we may very well build up a better cargo bike, like a Bakfeit, if Bettie 2.0 with the Big Dummy doesn’t work.

We’re hoping it does.

The Rohloff works well for off road tandems. I think it can handle a fully loaded dummy without problems.

Thanks Rikard. Our mechanic, the legendary Eamon Stanley, has been pushing Rohloff. I refused it for the Modal, but I think it’s a definite consideration for Bettie 2.0.

I was trying to figure out what you meant by “whippiness”?

I googled around, because I know people call some bikes “whips”. Never gotten the term, and in fact it seems unrelated to your use of the term “whippiness”. 

I assume you’re talking about the flex in the frame when you turn the handlebars left and right?

The flex in the tail end of the bike, especially if you’re carrying a heavy load up high in the back of the bike such as on the rack.  This “whip” is caused by the side to side momentum of weight in the rear and will in some instances cause the front tire to want to skid or lift up the ground when performing quick precise turns or swerves.

The easiest way to detect this effect is by turning the steering wheel back and forth really quick while riding at a moderate speed. The bike whill “shimmy” and the front tire may even skid a little though it is generally safe.

The more upright the bike and the more weight high on the rear rack the more you’ll feel it. 

The solution is to keep the weight in the rear low, extend the wheel base and keep the weight balanced around or toward the rear wheel, all of which the xtracycle does pretty well.

In cars and motorcycles they generally call this “balancing”. To much forward and the front tire skids to much on a corner, to much in the rear and the rear wheels skid to easily.

With a bike you have the added element of frame flex and the height of the load balance which accentuates the whip like feel that is most apparent in performance cars and motorcycles.

So, am I generally correct in my understanding?

@Michael

I define whippiness further here [in this comment thread](http://bikehugger.com/2008/08/ridecivil_artwork.htm).

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