Introducing the T47 Bottom Bracket Shell on the new Cruzbike V20c
The Cruzbike Vendetta V20c (released 2022) contains very significant updates including:
- A carbon fiber fork, chainstay and boom ("the front triangle")
- Thru-axles instead of skewers
- A tapered head tube which is thicker/stiffer.
All of these changes are designed to make the bike lighter, more efficient, and handle better. However, perhaps more significant than any of these is the adoption of the new T47 bottom bracket (BB) shell standard.
The BB shell is at the heart of power production on all bikes. Keeping Cruzbike's flagship racing bike up-to-date with the latest technology is essential for defending our claim to the fastest recumbent road bike in the world. Here's the story on why we have adopted the T47 BB standard.
Every other Cruzbike in our 17 years of making bicycles has used the 68 mm English-threaded BB shell, also called "BSA". In recent years, many manufacturers have been moving to BB shells with larger diameters and widths because they are more rigid and will accommodate the new larger diameter hollow crank axles (spindles) for lighter weight and more stiffness. Another big reason is the ability to place the bearings "inboard" rather "outboard" (where they stick out from the BB shell).
Our new T47 BB shell is over 25% wider and has a 39% greater inner diameter than our old BB shell. Now there is plenty of room for the use of modern cranks (with 30 mm spindles) AND inboard bearings.
We also chose the T47 standard because it's threaded. After many years of experience with press-fit BBs, the verdict is in: they are more prone to squeaking and are much more difficult to repair or replace, requiring the special tools and skills of a bike shop mechanic. Threaded BB shells like the T47 are more accessible to amateur hobbyists and are less likely to come loose and squeak. A larger inner diameter BB shell also allows for use of larger ball bearings, which last longer with lower rolling resistance. Major companies like Trek have switched to the T47 BB standard.
Because the T47 is threaded, the shell must be made from metal. You can't cut threads into carbon fiber. But this weight trade-off is definitely worth it.
Here are a few BB shell standards for comparison:
|BB Shell||width (mm)||inner diameter (mm)||% change width from BSA||% change ID from BSA||type|
Our T47 BB shell is 85.5 mm wide and has an I.D. of 47 mm. The thread pitch is 1 thread per mm.
A large variety of affordable tools are available to remove or install a new BB into the T47 shell.
Below is a photo of the stock V20c with the BB and crankset installed in the T47 BB shell, and clamped into the carbon fiber chainstay. Use a 16-notch 48.5 mm wrench for this BB. Just like the old BSA BB shell, the right (drive side) threads are left-hand threaded and the left (non-drive side) threads are right-hand-threaded (clockwise to tighten on the non-drive side).
It's worth noting in the photo above that the extra width of the T47 BB shell allowed us to increase the clamping surface area and width, making for a stronger and stiffer connection between the boom and chainstay.
If you are building a V20c from a frameset, look for a T47 compatible bottom bracket and crankset like the SRAM DUB. There are many other compatible high-quality bottom brackets and cranksets on the market. Another advantage of have a larger BB shell is that not only will they fit the larger spindles, but they will easily fit "old-school" smaller spindles if that's what you want to use. For example, if you love your old SRAM GXP crankset, you could buy a BB like this one (image below) and install it on your V20c.
Since 2005, Cruzbike has been delivering innovative solutions to make cycling faster, safer, and more fun. The addition of the T47 BB, plus all the other important V20c upgrades, make this version of our flagship Vendetta model the best ever.
Glad to see that Cruzbike is continually improving the bikes!
My only other comment is that a lot of folks have added racks etc to their V20’s for ultra fast ultra distance rides, and tail fin fairings, it would be nice to have some rack bosses on the frame for that vs the rube goldberg adaptations people have come up with. Even though the S40 is built for this, some folks just want one bike.
But yeah, looks cool! And the thru axle and the new BB shell are the way to go.
This looks like a definite step forward for the Vendetta series. Any thoughts on incorporating any of these upgrades on the S40 (or any other models for that matter)?
Has Cruzbike had an opportunity to conduct any type of fatigue life-cycle or maximum load testing similar to testing done on carbon cranks and diamond frames?
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