Bicycle frame

The uncommon prone bike moves the cranks to the rear of the rider, resulting in a head-forward, chest-down riding position.

Step-through frames usually have a top tube that slopes down steeply to allow the rider to mount and dismount the bicycle more easily.

These alternatives to the diamond frame provide greater versatility, though at the expense of added weight to achieve equivalent strength and rigidity.

Inside routing, once only present in the highest price ranges, protects the cables from damage and dirt, which can e.g. make gear shifting unreliable.

A shorter chain stay generally means that the bike will accelerate faster and be easier to ride uphill, at least while the rider can avoid the front wheel losing contact with the ground.

There may be a small brace that connects the chain stays in front of the rear wheel and behind the bottom bracket shell, called a "chainstay bridge".

They may be relieved, ovalized, crimped, S-shaped, or elevated to allow additional clearance for the rear wheel, chain, crankarms, or the heel of the foot.

This style of seat stay was popularized again in the late 20th century by GT Bicycles (under the moniker "triple triangle"), who had incorporated the design element into their BMX frames, as it also made for a much stiffer rear triangle (an advantage in races); this design element has also been used on their mountain bike frames for similar reasons.

A wishbone design adds vertical rigidity without increasing lateral stiffness, generally an undesirable trait for bicycles with unsuspended rear wheels.

To complete the specification of a bicycle for use, the rider adjusts the relative positions of the saddle, pedals and handlebars: The geometry of the frame depends on the intended use.

Traditional geometry road frames are often associated with more comfort and greater stability, and tend to have a longer wheelbase which contributes to these two aspects.

This positions the rider more on the sit bones and takes weight off the wrists, arms and neck, and, for men, improves circulation to the urinary and reproductive areas.

With a slacker angle, designers lengthen the chain stay so that the center of gravity (that would otherwise be farther to the back over the wheel) is more ideally repositioned over the middle of the bike frame.

In modern mass-manufactured touring and comfort bikes, the seat-tube angle is negligibly slacker, perhaps in order to reduce manufacturing costs by avoiding the need to reset welding jigs in automated processes, and thus do not provide the comfort of traditionally made or custom-made frames which do have noticeably slacker seat-tube angles.

These frames tend to have steep seat-tube angles and low head tubes, and shorter wheelbase for the correct reach from the saddle to the handlebar.

Additionally, since they are not governed by the UCI, some triathlon bicycles, such as the Zipp 2001, Cheetah and Softride, have non-traditional frame layouts, which can produce better aerodynamics.

Roadster bicycles traditionally have a fairly slack seat-tube and head-tube angle of about 66 or 67 degrees, which produces a very comfortable and upright "sit-up-and-beg" riding position.

If the tubing label has been lost, a high-quality (chromoly or manganese) steel frame can be recognized by tapping it sharply with a flick of the fingernail.

Early aluminum structures have shown to be more vulnerable to fatigue, either due to ineffective alloys, or imperfect welding technique being used.

However, some of these disadvantages have since been mitigated with more skilled labor capable of producing better quality welds, automation, and the greater accessibility to modern aluminum alloys.

Aluminum's attractive strength to weight ratio as compared to steel, and certain mechanical properties, assure it a place among the favored frame-building materials.

The most popular type of construction today uses aluminum alloy tubes that are connected together by Tungsten Inert Gas (TIG) welding.

Butted aluminum tubes—where the wall thickness of the middle sections are made to be thinner than the end sections—are used by some manufacturers for weight savings.

[47] While not as light as carbon fiber titanium's can provide a more pleasant ride quality, making the material popular among cyclists seeking comfort over performance.

The ability to design an individual composite tube with properties that vary by orientation cannot be accomplished with any metal frame construction commonly in production.

[56] While carbon frames can be lightweight and strong, they may have lower impact resistance compared to other materials, and can be prone to damage if crashed or mishandled.

In the 1980s, an engineer, Frank Kirk, devised a novel form of frame that was die cast in one piece and composed of I beams rather than tubes.

Scandium improves the welding characteristics of some aluminum alloys with superior fatigue resistance permitting the use of smaller diameter tubing, allowing for more frame design flexibility.

Cloud, Minnesota, briefly offered a frameset made of beryllium tubes (bonded to aluminum lugs), priced at $26,000.

For example, triple butted means the tube, usually of an aluminum alloy, has three different thicknesses, with the thicker sections at the end where they are welded.