BRIDGE Bike Works believes that a threaded bottom bracket is the best solution to avoid creaking and problems with your BB. But they also want to avoid having to bond in an additional aluminum shell into a carbon frame. Not only does that process add weight, but it still provides a chance for misalignment and potential separation of the shell down the road.
So then what’s the answer? Apparently, it’s to mold the threads directly into the bottom bracket shell itself. Fabrics
Today, BRIDGE announced a patent-pending integrally threaded carbon BB shell to answer that question. While the shell is based on T47-BB86, the say that they can apply the technology to any threads on the bike, including other BB sizes.
It’s bound to be a question – is carbon durable enough to serve in this function? To that, BRIDGE says that they have engineered the entire process from raw carbon, to molding, to curing to ensure that the final design will be up to the task. On top of that, when everything is done, the threads are treated with Cerakote. This abrasion-resistant ceramic coating should be capable of protecting the threads for repeated bottom bracket replacements if you need.
We’ll get more info on the process at Sea Otter, but BRIDGE is at least showing the BB mold and the threaded BB inserts that help create the carbon threads. More soon.
Zach Overholt is the Editor in Chief of Bikerumor. He has been writing about what’s new in the bicycle world for 12+ years. Prior to that, Zach spent many years in the back of a bicycle shop building and repairing nearly every type of bike, while figuring out how to (occasionally) ride them.
Based in Ohio, Zach is now slowly introducing a new generation to cycling and still trying to figure out how to fit the most rides into a busy schedule as a new dad.
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Is it normal to be this excited about threads?
I feel the same way. I love technology that satisfies my weight weenie obsession even if it is stupid expensive half the time. My wife thinks it is a mental disorder.
And what about a pressfit (or slipfit) BB with angular contact bearings ? With an adequate preload, there will be no creacking !
Skeptical would be an understatement… Better have a really good torque wrench.
You’d need a few hundred N-m to strip a 47mm thread in soft aluminum. This is probably much stronger than bad aluminum.
That said, all cyclists better have a really good torque wrench. 😛
Would you be out of Colorado by any chance
@Eric Heyl: I wish. South-east Michigan. With auto companies here, theres lots of good engineering jobs. And with that, the area has some really good trails. If you don’t have mountains, I guess you have to engineer them.
@SPJ: Thanks for the reply. Did you guys do any sort of CMM study to determine how repeatable you’re able to align the centers of the threads on either end of the BB shell? By having the thread molds on either end be independent, I’m curious how you’re able to perfectly align the two. The way I’d design the tooling is have the two halves thread together internally during molding, so that way they are repeatably aligned. Once cured, you’d back each side independently.
I totally get your skepticism. Skepticism is good. I had a pretty healthy dose of it regarding this design myself at first. However, I was in the building as this was being designed and tested. It passed a prolonged fatigue test with flying colours. But the bigger news as it pertains to the torque you’ve mentioned, is that it was also tested for sheer strength by threading in a BB to 150nm (that’s as high as that particular test rig went). The only thing that failed – after several attempts – was the alloy threads in the actual bottom bracket. Not the carbon molded threads in the BB shell. (Side note….. if you’re the kind a guy who owns expensive carbon bicycles, having a really good torque wrench is highly recommended anyway. 😉
i’ll let other people go first on this one.
“This abrasion-resistant ceramic coating should be capable of protecting the threads…” Should, could, would …
This will be a total disaster, people strip aluminium threads, these won’t last 5 minutes
I have a groundbreaking idea. Why not just get rid of the threads entirely?
Because press fit is kind of terrible. Note that the delamination problem is only a carbon problem. I know threads can get torn up I metal bikes but it doesn’t happen often and doesn’t typically happen in bikes that are actually taken care of.
Press fit is not terrible. It is manufacturers that cant meet tolerance requirements, which won’t change at all. However, I would still take threaded over PF any day.
If they can’t or won’t meet the required tolerances for PF than by definition PF sucks for bicycles from a real world ownership standpoint.
Press fit is only terrible if it’s not manufactured within proper tolerances, and is considered superior by most engineers. Companies that offer carbon frames with threaded BB interfaces are basically admitting that their manufacturing quality is poor.
Perhaps so, but from a real world ownership standpoint if they are persistently not going to meet the required tolerances of a proper functioning PF BB then PF is effectively crap for a bicycle owner. In theory, lots of things are great. At the end of the day all that matters is whether it is delivered to the customer in a consistent quality manner. In the bike industry PF BBs would be a hard NO as far as usable quality product from more than 9 out of every 10 CF frame makers out there.
Need to see a real world test. To me, the answer is to make bikes out of metal.
Manufacturing a proper ‘in-spec’ press fit BB interface probably requires half the precision that these fancy carbon threaded inserts do. I find this an absolutely baffling solution to a problem that quality manufacturing solves in the first place. Furthermore, what’s the weight savings over alloy inserts.. maybe 50 grams?
Imagine the BB cup installation care required to catch the first threads without cross threading… yikes!
I think this was developed mainly as a marketing ploy. Like you said, making a correct to spec PF hole has to be exponentially easier than doing CF threads, but PF BB’s in general have such a bad rep from most manufacturers that I’m guessing this was a way to get around that stigma and simultaneous claim that weight is also saved over a traditional threaded and bonded threaded BB cups.
Close enough to graphite to technically be self lubricating.
I built a few frames with molded bb shells (standard 68 bsa, not T47 obviously) back in 2006-2007. I found that properly isolating the two materials (carbon fiber and aluminum alloy) was the biggest challenge. Even the nickel plated Campagnolo cups had issues. After a few months of testing in wet salty conditions, even double anodized bb shells would start to form galvanic corrosion. The worst part was when you try to unthread a bb cup that has started to corrode it would completely destroy the threads and in one case completely split the whole bb shell. The best cups were the entry level Shimano square taper bb’s with plastic cups! Cerakote might help this issue, but I’m not all that hopeful as the application will need to thoroughly cover all the thread peaks and valleys inside the shell. Also hopefully the larger diameter and longer threaded portions of the bb cup will help them stay tight, the old short cups and flexy bb spindles of the past really didn’t fair well with carbon threads.
However I found that carbon bottle boss threads worked really well when using steel or carbon bolts with grease and titanium with bronze based anti-seize!
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