While this did the job, even under powerful sprinters, it didn’t do the bottom bracket any favours in the weight department. To obtain sufficient strength, the spindle was usually made from chrome-moly steel with very stout walls, and many spindles were solid steel all the way through. The skinny 17mm shaft found on most square tapered spindles also stood as a limiting factor for those looking to improve the stiffness-to-weight ratio in this area. You’d often encounter tolerance issues and the taper itself would change over time, allowing the cranks to slide on too far. While this design was good for bearing longevity, the square taper interface between the crank and spindle tended to be problematic. This is comparatively thin by modern-day standards and the skinny spindle left plenty of room for bearings between it and the bottom bracket shell. The spindle itself was usually 17mm in diameter. Go back around 20 years and most good quality cranks relied on a square tapered interface to connect the arms to the bottom bracket spindle. The inner diameter is roughly 34mm and for road bikes the shell is 68mm wide (the mountain bike version uses a 73mm wide shell).Ī little background on this ‘old-school standard’ will help to explain how bottom brackets have evolved and why we now see so many new systems popping up. To fit this system a frame needs a 1.37 x 24 TPI thread on the inside of the bottom bracket shell. If you’ve been tinkering with bikes for a few years, there’s a good chance you’ll be familiar with the English/BSA standard. What follows is a rundown of the features, benefits and idiosyncrasies of the current day bottom bracket systems. The manufacturer’s choice will influence how you go about servicing the bottom bracket and it may also impact your choice of cranks. Your bottom bracket system is determined by the bike frame and manufacturers usually tie their allegiance to a particular standard, touting the advantages of whatever system they choose. Adding to the mix we now have a Press-Fit BB86, BB90, BB30, Press-Fit 30, BBright and BB386 EVO. Nowadays the threaded English bottom bracket lives on but it’s nowhere near as popular-in fact this once dominant standard is now in the minority on new model upper-end road bikes. Some frames would require an Italian bottom bracket and more recently you’d see the occasional BB30 system, but that was about it for the mainstream brands.
Yes, there have always been a few left-of-centre systems but through the 80s, 90s up until the early ‘noughties’, the vast majority of road bikes relied on the English or ‘BSA’ bottom bracket standard. For decades the bottom bracket standards found on road bikes were just that relatively standard.
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