7005 aluminum is an aerospace grade aluminum that is 5-10% stronger
than 6061 aluminum by most measures. Double-butted tubes are specially
drawn so that they are thicker at the ends of the tubes, where they
are welded and stresses are highest, and thinner in the middle to
minimize weight. The process of drawing and butting tubes also work
hardens the aluminum. Work hardening is a restructuring of the material
at the molecular level when the material is heated to a specific range,
for a specific length of time, and stressed to a specific degree.
Work hardening increases the strength of 7005 aluminum by roughly
20%. Double butted 7005 tubes therefore, are significantly stronger
than equivalent weight plain gauge 7005 or 6061 tubes. Double butted
tubing allows frame designers to build strong, but exceptionally light
Sonus tubing further increases strength and torsional rigidity with
a custom profile. Sonus tubing is used on the main tube of all Dahon
folding bikes and is massively oversized with a flat base. Sonus tubing
increases strength and torsional rigidity by over 30% compared to
comparably sized oval tubes.
4130 Chromoly Steel
When it comes to "liveliness" and road feel, quality steel
is still the material of choice for many discerning cyclists. A well-built
steel frame can last a lifetime. Almost all steel framed folding bicycles
are made from low-cost high-tensile (also called low-carbon) steel.
Dahon only uses drawn (work hardened), 4130 chromoly steel, which
is 60% stronger than high tensile steel. Because of our chromoly tubing's
significantly higher strength, we can use thinner, and therefore lighter,
tubing. 4130 chromoly is why our steel framed bikes feel so "right"
and weigh less than many aluminum frame bikes from other manufacturers.
Puro U6 Aluminum Alloy
Puro U6 aluminum alloy is 25% stronger and 20% more fatigue
resistant than traditional 6061-T6 aluminum alloy. We worked with
the suppliers of this material to develop custom tubes for our SlipStream
fork, the lightest aluminum fork on the market.
6061-T6 aluminum is the workhorse of the bicycling world. It is used
to manufacture everything from frames to stems to cranks. It is relatively
light, plentiful, and easy to work with. Most aluminum frames are
made from plain gauge 6061 tubing. All Dahon aluminum frames are now
made using Sonus 7005 double-butted tubing.