From the WW I era to the 1970s, U.S. made bicycles, often of very high quality, were built to rather different standards than those that prevailed in the rest of the world. These bicycles used different standards for bottom brackets and cranks, frame tube diameters, seatposts, pedals, headsets and handlebar stems.
When the 1970's bike boom brought large numbers of European (and later, Asian) bikes to the U.S., the older American dimensional tolerances went into retreat, and were increasingly relegated to department store bicycles, such as Huffy and Murray. People began to associate the American dimensions with these low-end bikes, and to forget that many high-quality machines had been made to these standards. While the European bikes were undeniably lighter and faster, the better American bikes were made with a greater emphasis on durability and ruggedness.
BMX bikes are still largely made to American dimensions, and the BMX segment is one of the key sources for American sized parts. The early ancestors of the mountain bike were based on older American "cruiser" frames, and many early purpose-built mountain bikes used these standards.
The most distinctive part of this type of bike is the one-piece steel crank. The better ones are a solid forging, incorporating the left arm, axle, and right arm in a single piece of steel. These are the strongest cranks available. This is what makes them popular for BMX and children's bikes that are subject to rough usage. They are also the only type of crankset that can be serviced with ordinary household tools...all you need is a large adjustable wrench and a screwdriver.
InterchangeabilityThere are two major types of one-piece crank sets, differentiated by their threading. The more common size uses 24 threads per inch, but some bikes, particularly older U.S. made Schwinn and Mongoose models, use 28 threads per inch. No part of the bearing assembly is interchangeable between threadings.
The pressed-in cups are also a different size. It is usually a good idea to buy a whole set (cones, cups, retainers) if there is serious wear to any of the parts. These are not expensive.
24 tpi cranks (with the exception of Tange brand, which use #64 9-ball)
use #66 retainers, with 10 5/16" balls
28 tpi cranks use #64 retainers, with 9 5/16" balls.
Note: any frame that will work with one of these sizes will also work with the other. The compatibility issue is with the actual one-piece crank, not the frame.
UPDATE: There are now cheap dept. store bikes that have a smaller diameter one piece bottom bracket shell. The BB parts we sell will not fit this new, small diameter shell.
The 24 tpi thread size fits almost all one-piece cranks except for the original-equipment cranks on older U.S. made Schwinn and Mongoose bikes.
Conversion KitsIf you wish to upgrade a bike built for one-piece cranks to use modern 3-piece "cotterless" cranks, you need a "conversion kit." This consists of a special bottom bracket axle and associated bearing parts that can be pressed into a one-piece-crank type frame.
These beautifully machined aluminum bushings fit into the shell of a one-piece-crank bottom bracket, and are threaded to accept a standard threaded bottom bracket, normal 68 mm width. 3 long CrMo bolts connect the two bushings to one another for a secure mounting.
This saves weight, improves shifting, and allows the use of modern clipless pedals.
Be the first kid on your block to put a Dura-Ace crankset into your Schwinn Varsity!
American-style bikes generally are built with thinner tubing than foreign ones. The compensate for the thinner diameter by using tubing with thicker walls. The frames tend to be plenty sturdy, but a bit on the heavy side. The thick-walled tubing lended itself to welded construction, which was not possible with thin-wall tubing before the development of TIG welding and similar processes.
Since American style frames use smaller tubing diameters, they also need to use skinnier seatposts. The most common sizes are 7/8" (22.2 mm) and 13/16" (20.6 mm)
Wald 13/16" (21.15 m) Seatpost, 10-1/2 inchesMany older U.S. made bikes take this thin size. Unfortunately, there's very little choice in this diameter.
The top end is enlarged to 7/8" to fit standard saddle clamps.
Since one-piece cranks have to be able to fit through the bearing cones for assembly, the cranks cannot be as thick as three-piece cranks. As a result, they have to use a smaller diameter pedal thread, 1/2" instead of 9/16".
A traditional pedal with classic look.
A traditional pedal with classic look.
American-style bikes use the same headset threading and diameter as ISO standard (British) headsets, also the same 26.4 mm fork crown race size, but the frames have larger diameter head tubes.
Threaded Headsets (Yellow background indicates interchange problem) Size
Notes BMX/ O.P.C. bikes .833"
26.4 mm 32.7 mm 24 Older American Bikes 1" ISO Standard (25.4 mm) .875"
26.4 mm 30.2 mm 24 Modern standard size 1" J.I.S.(25.4 mm) .875"
27.0 mm 30.0 mm 24 Older or lower-quality bicycles from Asia
Headset 1" Threaded (21.15mm I.D.)Basic steel threaded headset for older American (OPC) bikes.
American-style bikes have thicker steerer tubes than Euro bikes, so they take thinner stems. The usual diameter is 21.15 mm vs the British 22.2 mm size. The stems listed below are this size. Sorry we don't have more to choose from, but these are getting scarce.
The handlebar clamp diameter of American stems is usually the ISO standard size, 1"/25.4 mm, or, in BMX applications, 7/8"/22.2 mm, so matching bars to stems is not commonly a problem, as long as the stem fits the steerer.
Alloy/Steel Stem SM242Ideal upgrade for your Schwinn Varsity or other older bike that needs the 21.15 quill size.
Aluminum upper section to keep the weight down, with strong steel quill.
Forward Exension (reach) 3" (80 mm) Weight: 440 grams Clamp fits ISO standard 1" (25.4 mm) handlebar center.
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