It was 84-degrees for the ride home from work today, but just when I was due to shave my head again, this guy robs a Portland video store of its prized classic movie guns and escapes on a bicycle. By 2015, Portland’s goal is to have 30% of all robbery escapes occur by bicycle.

My own theory, based on his facial expression in that photo, is that this guy just really needed to use a bathroom and, finding no public toilet in the video store, stole the gun to put himself out of his misery.

So Danzig. When I started work on this frame, there was no such thing as BB30 or Press-fit 30. The original design was built around a conventional English bottom bracket. Though it looks like the original pivot configuration will work with an oversized bottom bracket, I’ve started to look at optimizing around a much larger diameter bottom bracket shell.

This means adjusting the lower pivot orientation, which is what I was up to late last night.

In case anybody’s curious, raising the lower pivot location kicks the axle path back further initially. This makes sense if you imagine your instant center–the middle of your pivots’ rotation–as the center of a giant circle. The higher up you move the instant center, the higher up you move the whole circle. And the higher the circle, the more your axle kicks backward during that phase of the travel. Here’s a better view of the same image that probably won’t make any of this any clearer, but what the hell. Everyone likes circles.

The red circle is our original pivot center. The blue circle is the revised, higher pivot. The green arrows represent how the height of those circles affects the shape of the axle path. Your axle path is only a slice of pie cut out of that circle. Where you cut it changes how the bike pedals and rides. Completely. Important pie.

So that’s what I’m pissing with currently. Axle path–our slice of the circle–is also directly related to the force of the chain that’s trying to pull the bike together. If I find some magic extra horsepower to stay up late again tomorrow night, and if I’m not arrested for robbing a video store or run down by a perp pulling a daring recumbent getaway in North Portland, we’ll add that force to our circles.

My body’s starting to ask some tough questions about this whole commuting thing. I’ve ridden a bike to work for years now, but that was all chickenshit. Chicago’s winter was no fun, but I was only a few miles from work. Same thing with my first months in Portland. But the new dozen miles one way thing is a whole different kettle of fish. And sometimes watermelons.

So far, this that watermelon is the weirdest thing I’ve seen thrown from the 205 bridge. So far.

I’m writing a lot of product copy right now, and my research seems to be teaching me more about web sites than products. I’ve noticed, for instance that every sites offering live chat pretty much use pictures of the same dozen women wearing phone headsets. In fact, I believe that the entire female cast from the “Simply Irresistible” video now does web chat support.

OK, so yesterday I seem to’ve been typing something about Danzig’s instant center. To wrap that up, here’s the full migration of the IC from unladen to just under five inches of travel.

Not my best hasty animation, but should be good enough to give you the idea. It all comes down to this: the orientation of Danzig’s lower linkage tracks along the line of the chain as the rear wheel moves upward relative to the chain’s fixed point on the chainring. In other words, the instant center stays exactly along or very close to the line of torque (the chain) throughout most of the travel. What the hell does that do? Who knows until we actually ride prototypes, but it would stand to reason that maintaining an instant center that tracks along with the line of torque could be very desirable traits. Because the instant center stays so particularly focused right on a relatively small area throughout the entire first three inches of travel, and because it’s orientation is so particularly vertical, the system should be more consistent in all gear combinations, too–that’s just one of those obsessive details I tried to accommodate in the design.

That’s a pretty magnified look at only one tiny aspect of the system. Any suggestions or questions about other aspects, just let me know, and I’ll do my best to answer all questions. More next week.

Hank Matheson from Bicycle Fabrications let Dirt Rag take the wraps off his wild new “2D” suspension system today, and bravo. It’s sufficiently bizarre to have warranted the cloak and dagger. I love that it’s part homage to the old Cannondale Gemini DH frame, and that it’s legitimately something completely different.

Matheson developed it with engineer John Heim, and the truly unique thing about it is the axle path–or really axle paths. The suspension moves vertically, but it also moves horizontally. Square-edged hits allow the rear triangle to kick backward up to 19mm. The whole thing pivots on a large eccentric, so essentially it’s a single pivot on a pivot. The large eccentric onto which the swingarm pivot mounts can rock backward, and that motion’s controlled by a giant elastomer.

I have to admit I’m always a little envious of DH frames because there’s just so much you can do with them. You just don’t have the same chain growth and gear combination concerns.

Today’s Danzig detail deals with instant centers and gear combinations. Draw a line through the pivots of each of your rockers, find the place where those two imaginary lines cross paths, and you have your instant center. Unlike a single-pivot frame that has a fixed instant center, frames with multiple pivots have instant centers that move around. Where that instant center is relative to the chain you’re pulling along between your chainring and whatever cog you’re in dictates how the suspension behaves. Here it gets a little hairy, but the bottom line is that it’s desirable to build a happy relationship between that instant center point and the “line of torque,” i.e. your chain.

A key aspect of the Danzig design is the position of the lower link and how it affects that moving instant center’s relationship with the chain. Danzig’s lower link is basically the mirror opposite of every other lower link orientation out there. This orientation doesn’t just put the instant center right on the line of torque. The way the pivot rotates actually tracks alone with the line of torque as your wheel raises.

Clear as mud, right? For now, here’s the resting point of the instant center (the red dot). Next, I’ll blow out some other drawings so we can look at where it goes when the suspension is compressed and why I worked hard to get it to do that.