## Tuesday, August 24, 2010

### Double-butted when you spoke? Part I

I apologize for the pun in the title of this blog. We are going to look at bicycle spokes today.
• spokes are wires which are woven between a hub and a rim to create a wheel
• spokes usually have a bent head that keeps the wire from coming out of the hub
• spokes have a threaded end which goes through the rim and engages a nipple
• spokes can be straight or single-butted, double-butted or triple-butted
• spokes can be have oval or flattened shapes in the middle of their length
• spokes should be rust-resistant, strong, light and have some flexibility
Here are some spokes and nipples. This handful is about the number you need for a single bicycle wheel. And here are the side views of each end of two kinds of spokes - the flattened aerodynamic type and the normal round style - and some nipples.
A butted spoke is thick on the ends and thinner in the middle. This saves weight, reduces drag and adds some flexibility to the wheel.
• single-butted spokes tend to be thick at the hub end, thinner in the middle, and maintain that thickness to the rim (threaded) end.
• A double-butted spoke is thick at the hub end, thinner in the middle, then returns to the original thickness at the rim end.
• A triple-butted spoke is thick at the hub, thin in the center, and a third (thicker) diameter at the rim end.
The aero spoke is flattened to reduce wind resistance. If it's too flat, it won't fit through the holes in the hub, so there's a limit to the flattening.

OK, I think that's enough background information. Now it's time to ask, "Do we need math to make a bicycle wheel?" Probably not, right? I haven't provided any numbers.

No, it turns out that you need a surprisingly large amount of math. Wheel (we will) look at the issues more closely tomorrow.

PS - I guess it's unfair to have NO numbers at all, so here - you've heard the phrase "let's not re-invent the wheel." Why not? Because everyone else is. I did a patent search and found 4668 patents on bicycle wheels!