Over the last year I’ve had a considerable amount of communication with Mark DiNucci. It began with the reboot of the Allez and continued well beyond that and into what I’d call a graduate correspondence seminar for the armchair frame builder. This coincided with an order for a frame, which became an education in frame prep and care unlike anything I’ve ever received. Rather than try to interpret his views, I gathered some of his communication and am presenting it here. His clarity of thought and mission, in unromantic and objective terms, is rare even for this crowd—Padraig.
“All truth passes through three stages. First, it is ridiculed. Second, it is violently opposed. Third, it is accepted as being self-evident.”
The best material for bike frames is also the best material for springs. These include titanium (Ti), steel, carbon fiber (CF). The reasons for using an efficient spring in a frame is to offer a form of suspension over surface irregularities, an efficient return on energy used to accelerate the frame, and to offer the best fatigue life.
Steel and Ti are used for industrial springs in military and domestic aircraft, high level motor sports, marine environs and other places where the need for reliable fatigue life is important when human life may be at stake. You will find CF being used, for example, as a suspension leaf spring in some Chevrolet Corvettes because the spring can be made without overcoming its layup restrictions.
Why I Choose Steel
I have developed a set of proprietary new designs for the all of the tubes used in my frames. One of the objectives these new tubes were designed to offer is the best combination of the lively and comfortable suspension qualities that may be obtained from the use of high strength steel’s unique properties.
The “stiffness” of steel is basically the same for low strength and high strength steel. A frame constructed with low strength steel, with the same chassis’s structural strength as a frame made with high strength steel, will weigh more. It will also feel lifeless when compared to the lighter frame because it will not flex as readily over surface irregularities. Because the tube can be designed to flex the properly designed high strength steel tube set will absorb road shock, before it springs back, which takes some of the load off of the tires giving a more efficient ability for the bicycle to roll. The tire itself is a fairly efficient, slightly damped, spring. If the frame allows some of the force that impacts the tire to be displaced through the frame it allows the tires suspension abilities to be momentarily increased which adds to the desired ‘effortless’ rolling effect.
In order to achieve this desired, lively and comfortable, suspension effect my new tube set is designed using the most thin walled tubes that are practicable for real world use. The design allows the tubes to be more thin walled at the joint than a tube designed to be welded. The lug adds, on average, roughly as much weight as is saved when using the lugged design compared to the most simple welded design. For example when comparing my lugged frames of average to larger sizes, with those using one of the welded methods, the lugged top tube / head tube / down tube assembly will not weigh more because of the design of my thin-walled tubes. My lugs offer the distinct advantage of being able to add controlled strength to the areas that benefit from it while decreasing, or more efficiently using the mass near the highly loaded areas that are inherent in the welded joint design. My lugs are effectively another butt.
For example, look at my head tube to down tube joint. This is the most highly stressed joint on the main frame. Among other salient features, my lug design exhibits a very long tapered point under the down tube in order to add the desired strength to portions of this area, and to move the loads further away from the head tube / top tube joint in a carefully engineered manner. It should be readily apparent to those who are familiar with fabrication why these long points are very expensive to correctly manufacture. The lug angle must be manipulated to match the design angle while retaining a perfect fit. This is an additional time consuming manufacturing step. You may notice that most lugs have much shorter points. The short lugs are relatively easy to match the frame design angles to and are more easy to braze. This is probably the reason you will rarely see long point lugs. My new lugs also employ an engineered, tapered portion that embraces the head tube with progressive strength. This allows the head tube to have a greater diameter to wall thickness ratio than other designs currently available, which saves approximately 20 to 30% more weight when compared to the other available head tubes, while retaining enough strength to accommodate the increased loads presented by the modern one and one eighth inch (28.6mm) fork steerer tube. Compare the perimeter of this lugged joint to the perimeter offered by a welded joint and you may begin to understand how much stronger my lugged joint is than a joint using one of the welding methods. My lugs are, in essence, another butt and have been engineered to use this very beneficial attribute. The loads are spread over a much greater area, in a completely controlled manner, thereby decreasing the stress risers the tube will see which results in the best fatigue performance, the best creation of a spring, and the most beneficial use of mass (weight). Knowing the tubes can be parametrically modified during the design of the lugs allowed a synergistic ethic to be employed. The tubes and lugs have been designed with the advantages and disadvantages of each component taken into account, simultaneously, and then this information was used to create this new design.
I usually use low fuming bronze (brass) brazing on the main triangle joints (and frame/fork ends) in order to best use the advantageous properties of the air hardening steel. When heated to an adequate temperature and allow to cool at the proper rate the strength of the material increases while retaining stated elongation. This in effect, gives an additional, invisible after painting, butt that is located at a very advantageous location around the perimeter of, and under the lug. This effect was considered when designing the lugs. This bronze brazing process is more time consuming, for many reasons, then when using silver braze. This localized heat treating process offers additional strength and fatigue life to the joint. This feature is not visible except after shot peening, when the surface shows it’s increased hardness. I am often reminded by people who are involved in marketing that, “A feature which is not visible is not a feature with a benefit to the customer.” I disagree with that statement.
I have tried to be as responsible as possible to all of the aspects of ownership when making the myriad of design decisions that were made during this process of bringing this new frame to life. These tools do not fit the rider to the frame or create the frame geometry that satisfies the riders desired goals. They are probably the most advanced tools to be used in the construction of lugged bicycle frames but they are only pieces of steel until they are combined with the skills needed to bring a riding experience to life.