So, we’re collecting all the parts required to build our first test-of-concept frame: the Seven Cycles Shop Bike I mentioned last week. Our intention was to source the four lugs and maybe build one from scratch; making a lug from scratch was to be part of our conceptual test. Well, it turns out that we can’t find a single lug that will work on this shop bike—not even one.
We’ve looked at too many lug sources—through suppliers and direct from manufacturers, domestic and overseas, road and mountain, high quality and cheap—and cannot find a single lug that will work on any of the four joints that would typically get lugs. “What the what?” This bike design is completely within Seven’s norms. In fact, we tried to design the geometry so that we could use some standard lugs. Still, no dice.
I’m sad to say that this is one of the more enlightening moments of the project for me—and for many others in the Collaborative. Here we are trying to design a bike—a fairly average bike design, by Seven’s standards—and we can’t find a single lug that will work.
What Are The Four Lugs?
For those that don’t know what I’m talking about, the four common lugs are:
- Head tube to down tube
- Head tube to top tube
- Seat tube to top tube
- Bottom bracket to seat tube and down tube
[If I had time I’d include a diagram. Maybe later.]
Why can’t we find lugs? The basic reasons include:
- We want to have this bike employ a “compact” design with 12 degrees of top tube slope. Yes, this is a bit more than average—Seven’s road bike average being about 8.5 degrees. But, over the years we’ve built thousands of bikes with 12 degrees or more of slope. And, apparently, lugged steel bikes must have an average of about 0 degrees of slope.
- We want to use a 1.25” diameter top tube. Yes, this is on the unusual side for a road bike. But, not for a mountain bike—and there are some mountain bike lugs out in the world. Two reasons we’re going with a 1.25” top tube: 1) This is a shop bike with a big rack on the front—front end torsion can be a challenge, and a stiffer top tube can help. 2) Because we’re butting in house, we can play with diameters, tube walls, and tube butts more so we want to experiment with this tube.
- We want to use a 1.25” diameter seat tube. Again, unusual but not crazy. We have our reasons: explaining later.
- Read between the lines.
So, in the end, even when we tried to compromise the design fairly extensively, we still couldn’t find lugs—actually, we found one that would sort of work. Therefore, we decided to design our ideal since we’d have to make lugs from scratch anyway. And, maybe a fillet joint or two—that’s a whole other conversation.