We love lugs. All of our frames use lugs of our own design.
What is a lug?
A sleeve of metal that surrounds the frame tube at the joint, strengthening the joint. Most modern frames don't have them.
They're more expensive to build with; and from a strictly practical point of view, they're unnecessary.
- What does a lug do?
It strengthens the joint by adding material to the stressed areas, and distributes the stresses over a large area. And it adds an artistic element to the frame joint. And it allows tubes to be joined by brazing, rather than welding.
- Why brazing rather than welding?
Less heat, mainly. One of the benefits is that the tubes themselves are not melted. So, if you crash and bend a top tube, for instance, it can be replaced and the frame made good as new. It comes down to this: Good lugged frames are 10x as nice to look at as welded frames are, and they're much easier to repair.
Is a lug a lug?
No more than a knife is a knife. Some are well-designed to eliminate stresses; others accentuate stresses. Some are thick, some are thin. Some fit the tubes well, others don't. They come in plain and fancy, available to anybody and proprietary. The can be made by investment casting, stamping and welding, die casting, and bulge-forming with high pressure oil, then laser cutting.
- Lugged joint vs tig-welded joint:
They're both strong enough. Lugs allow easy tube replacement. Tigged joints are fast and cheap and strong, but if you buckle a tube on a tigged frame, you replace the whole frame.