Bike lugs are the joints where the tubes of a bike frame. When one thinks of a beautiful steel bike it’s those joints that stand out even more than the finish. Traditionalists, and bike curmudgeons all agree a lugged steel bike is all you need – the ride is better – the lugged bike is where technology should have stopped. Yes, and air conditioning is a bad idea too, never mind the computer, tablet, etc, you’re reading this on. Is there really a difference in the ride or should lugged frames be ridden into history?
I don’t know, but they look nice. When I had the opportunity to work for the Casati family at the bike industry trade show several years ago, the patriarch of the family, Gianni, told me that a lugged frame was better for comfort and provided a nicer smoother feel. He said that the welded metal frames and the monocoque (single piece molding) carbon frames were better for power transmission for racing. Gianni was a contemporary of Ernesto Colnago, and recently passed away at the age of 80. Casati still produce both styles of frame. All of their frames are made at their shop in Monza, Italy and they only produce about 1500 frames a year.
In a lugged frame the lugs and the frame tubes are joined together by solder which is run in between the lug and tube. This building technique is called brazing. Brass or silver is used for the solder material. Welded frames have the tubes welded directly to each other. Fillet brazed frames use a solder too, but tubes are joined without a lug. My into the history of lugs research turned up Dave Moulton’s blog. Dave started racing bikes in England in the 1950s and was a national class racer. He learned to build frames in the late 50s and by the 1970s his frames had been ridden in the Tour, Olympics and Worlds. He no longer builds frames, but he comments on bike history and other topics. In his bike design history article Dave wrote, “Frame lugs were heavy steel castings, machined on the inside to accept the tubes at these (what became) standard angles. It was not cost affective to make lugs in different varying angles. It was established probably around the 1930s that 73 degrees was the ideal head angle for a road bicycle; this is still true today.” Dave explains that bigger bikes ended up with shallower angles for the seat tube because of this. (for more see http://davesbikeblog.squarespace.com/blog/2009/10/5/the-evolution-of-frame-design-part-i-the-wheelbarrow-effect.html) Lugs today are made in more than one size so custom lugged frames use lugs that appropriate for the necessary geometry or are able to be carved on the inside to provide the proper angles needed.
Welded frames and lugged frames have both been around for a very long time. Schwinn made millions of inexpensive welded frames in the bike boom of the 1970’s. It was a much less time consuming and less expensive build process than using lugs. However lugs were used on lightweight thinner tubes because brazing can be done at lower temperature than welding and this keeps the tube itself from becoming weakened, or fatigued, by being over-heated. Tubes designed with more material where they are going to be heated and joined are called butted. The extra material preserves the tube strength. Dave Mouton comments, “A properly brazed lugged joint is tremendously strong and a lug spreads the stresses over a larger area, not pinpointed in one place as with a weld. This is also the reason lugs are cut into curved or other fancy shapes, and not just cut square like a pipe fitting. A square edge would create a stress point and the tube would likely fail at that point.” (for more see http://davesbikeblog.squarespace.com/blog/2006/10/3/brazing-vs-welding.html)
Aluminum and titanium frames do not use lugs. Both materials are welded and cannot be lugged. Carbon frames can’t be welded, but heat is applied to shape and cure the frames. Carbon frames came on the commercial scene in the 80s. Craig Calfee has been there since the beginning of carbon frame production. Calfee’s website provides the following, “Advanced composites are composed of engineered fibers such as carbon, polymer, metal, or ceramic. Usually these fibers are impregnated with a thermosetting resin like epoxy… their strength and stiffness is only realized along the axis of the fibers, which can be arranged in any desired pattern. Thus, to absorb the variable stresses of a given bicycle frame, composite frames can use multiple layers with different fiber angles for each. This puts strength only where it is needed while minimizing weight…Along with traditional round tube and lug frame designs, composite frames can be molded with the use of internal bladders and foam in either one-piece (“monocoque construction”) or multi-section frames. Also, they can be formed in a high pressure lamination process combining the frame tubes into one integral piece.” (for more see http://calfeedesign.com/tech-papers/technical-white-paper/) Because of these properties carbon fiber can be added as needed where needed. One-piece moldings cannot be customized, but molded lugs provide the freedom of design that traditional steel lugs and welded frames offer. It is hard to quantify what is best – it really depends on the rider’s needs and preferences. What is interesting to me is that the lug lives on in the highest quality frames available whether your preference is an elegant steel ride or a crazy light carbon.
Owner, Reparto Corse