The bicycle industry has been inundated with new bottom bracket standards in recent years, each of which is designed to enhance the performance qualities of a particular frame. However, we’ve often heard from our pro athletes and riders that this large pool of designs can often be confusing to navigate. We’re always striving to improve upon each and every bike we’ve built with innovative designs and thoughtful technology, and in our three decades of building bikes, we’ve learned that sometimes the best way to improve an aspect of the cycling experience is to do so modestly, rather than revolutionarily. That’s where our new bottom bracket adaptation—called T47 - 77 ASYMMETRIC—comes in.
First, it’s important to note that T47 - 77 ASYMMETRIC is NOT a new bottom bracket standard. It’s simply a new spacing adaptation to the existing T47 standard that is supported by members of the original T47 development group (see below). It utilizes an existing T47 internal cup on the non-drive side and an existing T47 external cup on the drive side.
T47 is a threaded bottom bracket standard developed several years ago by Chris King in partnership with Argonaut Cycles, Enduro Bearings, Engin Cycles, Paragon Machine Works, Praxis Works, and White Industries. Felt Bicycles was an early adopter of T47, utilizing the 86.5mm standard. Detailed information on T47 can be found on Chris King’s website, while an engineering drawing, as released by Chris King, can be viewed below.
T47 utilizes 47x1mm threads, and is available in both narrow (external cups) and wide (internal cups) formats. Here is how several leading bottom bracket manufacturers differentiate the varying formats within their product lines:
No. Like the original T47 bottom bracket standard, this new adaptation is intended to be public domain. All interested bicycle frame and component manufacturers are encouraged to use it for applications where its unique properties can be beneficial to the overall riding experience.
Chris King, Praxis Works, White Industries, CeramicSpeed, and FSA are all supporting brands of the new T47 - 77 ASYMMETRIC spacing adaptation.
Felt Bicycles believes in threaded bottom brackets and expressly understands the benefits and costs of the available bottom bracket systems and widths. From an engineering perspective, the 68mm standard is limiting on the non-drive-side from a tire clearance and frame stiffness perspective. For many categories and sub-categories, 68mm frame widths are still optimal. Also from an engineering perspective, 86.5mm frame widths, especially with BB386, can yield undesirable drivetrain interferences, and do not always offer significant drive-side value additions for frame performance metrics (specifically, stiffness, tire clearance, or rear-center geometry).
With all of that in mind, an alternative threaded solution to BSA (English threaded) was apparent. Felt is cognizant of the headaches that can accompany bottom bracket standard conversations, and we knew we didn’t want to add to that by establishing a proprietary solution that yielded new component and tool requirements.
Additionally, T47 - 77 ASYMMETRIC also offers a modest amount of increased frame protection in the event of a dropped chain or chain suck. This is because T47 - 77 ASYMMETRIC creates ample space between the chainstay and crankset so that the chain is less likely to become stuck compared with many other bottom bracket types.
T47 - 77 ASYMMETRIC utilizes a combination of 42.75mm (85.5/2) on the non-drive side and 34mm (68/2) on the drive side, establishing a total bottom bracket width of 76.75mm (~77). An engineering drawing of T47 - 77 ASYMMETRIC can be viewed below.
We’re hard at work on the next generation of Felt road, gravel, and triathlon bikes, some of which will feature the T47 - 77 bottom bracket adaptation. Stay tuned for more details.
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