Frame Technology

FRAME FEATURES
Understanding Frame Efficiency

TUBING 101
Comparisions
Tubing Refinements
Relative Weight Index
Developments

FRAME NOTES
Chromoly
Aluminum
Niobium
Scandium
Titanium
Carbon

The IsoGrid® Story

WHAT IS BUTTED TUBING?

Most single bikes, and a few tandems, are built with “double-butted” tubing. Buyers are often confused by this term, or think it’s just a weight-saving measure. Actually, a properly designed double-butted tubeset saves weight while increasing a frame’s stiffness, stability, strength and comfort. To understand this you will need to appreciate where and how a bicycle frame is stressed.

On a bicycle frame (or any structure), stress concentrates where the material is joined. When the joints are at corners, as with bicycle frames, stress is intensified. When joints are welded, there is further stress at the edge of the heat-affected zones. It’s no wonder bicycle frames break at the edge of the weld—this is where three types of stress (joint-, corner- and heat-) converge.

To prevent frame failure, designers specify tubing with a heavy wall thickness. However, the thickness required at the extreme ends of the tube exacts a large weight penalty on the rest of the tube (where stresses are much lower). Besides the weight penalty, thicker tubes also yield a harsher and less responsive ride.

The answer is double-butted tubing—thick at the ends and thin everywhere else.

Besides saving weight and improving comfort, double-butted tubing has another advantage, fatigue resistance. Because a thin-walled center section of a double-butted tube will absorb stress that would otherwise concentrate at the joints, the ends of a properly-designed butted tube can be thinner than a plain-gauge (unbutted) tube doing the same job. This explains how tandems built with Santana’s exclusive 7/4/7 tubes (.7mm thick at the ends and .4mm thick everywhere else) can dissipate stress better (and last longer) than tandems built from heavier tubing.