Wheels mfg Bottom Brackets

New frames and cranksets are released every season, and with these changes come new bottom bracket "standards". We once had a particularly frustrated shop mechanic tell us: "Something should be around longer than a week before they start calling it a standard!". While we tend to agree, it’s the reality of the bike industry. One of the most common issues we see is mechanics relying on the names of bottom brackets to identify which bottom bracket is right for a frame, rather than relying on measurements they take. Below we discuss some of the common pitfalls of relying on bottom bracket naming conventions only, and we hopefully clear up the three most common misconceptions about bottom brackets we see.   BB30 & PF30 While BB30 and PF30 frames have been around for a few years now, there are still many misconceptions surrounding them. Strictly speaking both are "press-fit" systems because neither one uses a traditional threaded bottom bracket shell, and they both were originally designed for cranksets with 30mm diameter spindles. However, this is where the similarities end. The BB30 system is a "direct-fit" bearing system where the outer race of the bearing directly contacts the frame. A BB30 bottom bracket simply consists of two 6806 bearings pressed directly into the bottom bracket shell of a frame with a 42mm inside diameter and usually employing 2 retaining clips to set the depth of the bearing. You can learn more about the BB30 bottom bracket technical specifications HERE. A PF30 frame has a shell slightly larger than BB30 (46mm compared to 42mm). The bearings are pressed into cups which are then pressed into the frame. In the case of the PF30 systems the bearing cups rely on flanges to ensure that both cups are pressed the proper depth into the frame. You can learn more about the PF30 bottom bracket technical specifications HERE. Adding to the confusion between the two standards is that many frame manufacturers do not publish the dimensions of their bottom bracket shells. They may publish the crankset shipped with the bike, but that doesn't tell us what shell is in the frame. Cannondale takes it a step further by putting a BB30 sticker on their frames regardless of it has a BB30 or PF30 system! So, it’s always best to rely on measurements. Yes, you may need to remove the crankset to do this, but better than guessing wrong. You can also contact your frame manufacturer who should be able to give the exact BB shell dimensions.   BB86/92, BB90/95 & PF92 BB86/92 and Trek's BB90/95 are often misidentified. While the "30" in BB30/PF30 references the inside diameter of the used, the numbers in BB86/92 and BB90/95 refer to the width of the frame's bottom bracket shell. The BB86/92 bottom bracket system uses a bearing pressed into a cup, which is then pressed into the frame. BB86 and BB92 bottom bracket shells always have an inside diameter of 41mm and a commonly used width of 86.5 or 92mm, but can be found in shells up to 132mm wide. More on the BB86/92 standard can be found HERE. The BB90/95 bottom bracket standard found on various Trek models is like the previously discussed BB30 system in that it is a "direct-fit" system. The frame's bottom bracket shell inner diameter is 37mm. A bearing with an OD of 37mm is pressed directly into the frame. Trek is moving away from the BB90/95 system to what they call PF92, which is the same as a BB92 (41mm ID shell and 92mm width). Again, we recommend taking inner diameter and width measurements on the frame to determine exactly what standard the frame has. More on the Trek BB90/95 standard can be found HERE.    Specialized OSSB OSBB is an acronym for "Oversized Bottom Bracket" used by Specialized. The problem with this term is "How oversized is Oversized?". In comparison to the previously discussed bottom brackets standards, this term gives us no dimensions to work with. OSBB has been used to describe frames with 42mm and 46mm diameters. Specialized frames with a carbon fiber shell construction are usually 46mm inner diameter (Carbon OSBB), and can have a width of 61mm (road), 73mm (mountain) and 83mm (downhill). Frames with aluminum BB shells (Alloy OSBB) have an inside diameter of 42mm and a widths of either 68mm (road) or 84.5mm (mountain). Specialized often simply uses the term OSBB for each frame. If you are trying to fit a bottom bracket in a Specialized, best that you measure the frame, or contact Specialized directly for exact measurements.   As we've detailed here, relying on names and terms to identify bottom brackets can be confusing at the least, and misleading at the worst. Relying on good solid measurements can make navigating the minefield of bottom bracket standards a lot easier. So, one word of advice when trying to identify a frame's bottom bracket standard it would be, always measure the frame, don't assume it is one particular standard.