Here is a one-piece crank and bottom bracket for a child's bicycle made by Roadmaster.
This appears to be an ordinary OPC bottom bracket shell, but is about 43mm ID and about 65mm wide.
This begs the question: how does this improve on the standard size? There are no obvious clearance issues where the extra 9mm of an American OPC would be problematic, likewise the extra 3mm of width. And while there is slightly more material cost in the larger shell and bearing races, a usual rule of thumb is doubling volume drops cost by 5%, and the volume of American OPC shells is huge compared to the volume of this, so despite the higher material cost the overall cost is likely much lower.
The great thing about standards is there's so many of them. — Unknown Shoot me now! Shoot me now! — Daffy Duck
Here are some other bottom bracket shell sizes. American OPC and ISO are by far the most common, with BB30 starting (as of 2009) to gain popularity on expensive bicycles.
| name | attributes |
|---|---|
| American OPC | 51.3mm bore, press-in; shell 68mm |
| BB30/Cannondale SI | 41mm bore, press-in; shell 68mm wide ("road") and 73mm wide ("mountain"). |
| BB83/BB86; BB92; aka "Shimano System" | 41mm bore, press-in; shell width 86.5mm ("road") and 91.5mm ("mountain"). |
| BB90/BB95 | Trek's Campy- (and Shimano-, SRAM-, FSA-) compatible Madone bottom bracket. The shell is 90mm wide by 37mm ID. 37mm OD bearings (the same bearings as inside an external-bearing cup) insert directly into the carbon frame and accept integrated-spindle cranks. BB95 is the MTB version of BB90 with a 95mm wide shell on the 2008 Trek Top Fuel and Fuel EX carbon. |
| British | 1.370" x 24tpi, right side is left-thread; shell 68mm/73mm |
| Fat Chance | ?? press-in cartridge bearing; shell ?? |
| French | 35mm x 1mm, both right-threaded; shell 70mm |
| FSA MegaTech | 50mm, press in; shell ?? |
| Eccentric | 54mm, no threads. Usually 68mm wide. Eccentric inserts are typically of three varieties: internal expanding; a smooth OD with setscrews in the shell or a pinch clamp; or an axial clamp. The shell bore tolerance is thus not precise and in practice varies from 53.5mm to 55mm. |
| Klein | ?? press-in cartridge bearing; shell ?? |
| Gary Fisher | ?? press-in cartridge bearing; shell ?? |
| Gary Fisher Eccentric | 57mm, no threads. Width 73mm. |
| ISIS Overdrive - I | M48 x 1.5, both sides right-thread, shell 68mm/100mm |
| ISIS Overdrive - II | M48 x 1.5, right side is left-thread, shell 68mm/100mm |
| ISO ("English") | 1.375" x 24tpi, right side is left-thread; shell 68mm/73mm |
| Italian | 36mm x 24tpi (mixed units!), both right-threaded; shell 70mm |
| Merlin | ?? press-in cartridge bearing; shell ?? |
| Mavic/Stronglight | ~45 degree taper collet, ~1.375" ID, shell 65-73mm(?) |
| PF30 | 46mm smooth bore, 68mm wide shell. Cartridge bearings sit in a shouldered plastic retainer that allows for lower tolerances than are needed for BB30, and which eliminates the BB30 circlip. This is, in effect, American/OPC with 46mm bore instead of 51.3mm bore. |
| Phil Wood American Isis | 50mm x ?? threaded; ?threading?; shell ?? |
| Raleigh | 1.375" x 26tpi, right side is left threaded; shell 71mm/76mm |
| Roadmaster child's | 43mm press in; shell 65mm wide |
| Swedish OPC | 45mm, externally-threaded; width ?? |
| Swiss | 35mm x 1mm, right side is left-threaded; shell 68mm. Same dimensions as French, but with right side left-threaded. |
Merlin and Fat Chance are probably the same, as the two shops were in the same cul-de-sac in Sommerville, MA.
Campagnolo, Cannondale, Fat Chance, FSA, Gary Fisher, Klein, ISIS, Merlin, Mavic, Phil Wood, Raleigh, Roadmaster, Shimano, SRAM, Stronglight, Trek, and any other trade names are trademarks owned by their respective owners.