Nature Boy Disc Dropout: Finessing the Form
Sorry for the massive delay between posts. I wrote this post, accidentally deleted it, and then a big pile of design deadlines got in the way. Had to work on Koochella team stuff. Excuses, excuses.
But I think you'll find that this installment is well worth the wait because of: New Sales Guy Adam-Enhanced Photography!
Since Frostbike, we’ve picked up a new team member (I’m sure he’ll be formally introduced any minute now… on a blog or something).
His name is Adam. He races track, drives a pick up truck, and is, for all I know, an excellent breakdancer.
Having a formal education in Photography, Adam watched with a pained look in his eye as I juggled prototypes while trying to take pictures for this entry.
“Do you want some help?”
I responded, totally maturely, by muttering about being an engineer, not a photographer… and some stuff about how it was important to have consistent shitty photography across all my blog entries.
“Those would look better in natural light.”
After two or three extraordinarily crappy shots on my phone, I grunted, gathered up the prototypes, and went to the window.
Adam was right. Thanks, Adam, for being better than me.
Back to Our Story: The Dropout Body
The first concept, seen below, was the “blended” concept I discussed in the last installment. It was flat like the Hennepin Bridge rear facing dropout, but it had the same three-dimensional interfaces as our other dropouts.
It was also super long and tall. It was initially compatible for 140mm minimum rotors. I sketched in random pockets on the inside of the dropout to try to save weight, but the pockets didn’t save a ton and when I started to optimize them, they didn’t look clean.
You’ll also notice pen marks on the dropout. When people give me design feedback, they like to draw on my prototypes without asking. Which makes them not perfect and clean… and drives me crazy.
Anyway… to improve the stiffness of the dropout, I hollowed-out the body. I also killed the flat spot at the front of the axle pad where the tensioning spring interfaces. Why? Well… it improves the strength of the dropout pretty substantially. Also, after making some prototypes and checking, we found that the spring operated effectively even when compressed against a non-flat surface.
Oh, and we put the chainstay drainage hole on the bottom of the dropout. Why? YOLO.
Just kidding. With the hollow body there wasn’t really a logical spot to place the drainage hole on the inward-facing side of the dropout (where I typically like to put them). Anywhere on the inside of the stay that seemed visually appropriate wasn’t functionally appropriate. I aim to place drainage holes in the lowest point of chainstay when the bike is hanging so that the water doesn’t pool anywhere weird and that wasn’t going to happen on the inside of the dropout. The deepest part of the pocket, unless I decided to fill it in, was on the bottom. It made sense. I couldn't think of a reason not to do it.
The dropout remained pretty large until late in the process when two critical decisions happened:
1) We increased the minimum rotor size from 140mm to 160mm.
2) We decided to invest more time in the design of our post mount adapter due to this feature we were adding. A forged adapter can be more complex in shape than a simple laser cut one. This opens the door for formal optimization. Also, forged adapters are stronger due to the nature of the process.
When you increase the minimum rotor size, you move the physical caliper away from the rear axle. This reduced clearance issues between the caliper and adapter mounting slots and allowed us to shrink the height of the dropout (less wrench clearance is needed). Then, when we invested in the development of the adapter, we were able to increase the size of the aluminum adapter while shrinking the steel dropout… which helped reduce weight.
This is where I'm leaving this entry. I originally had it paired up with the next entry but I was even glazing over reading my own discussion about the post mount adapter development after this stuff.
Anyway, the next/last entry is all about the custom post mount adapter. It really ties the room together.