Bottom brackets

Noah_Deuce wrote:Press fit are notorious for squeaking.  http://www.bikeradar.com/us/road/gear/article/angryasian-ive-had-it-with-press-fit-bottom-brackets-38220/

There are some aftermarket solutions. http://www.praxiscycles.com/conversion-bb/ or http://www.bbinfinite.com 

But I tend to agree with your LBS - why set yourself up for the headaches and annoyance?  Also, a Shimano XT or Ultegra bottom bracket costs $30-ish, you can install it yourself, and you know that it will work for a long time.

If your heart is set on the carbon bike, then by all means, go for it!  But know that your BB may be more finicky or require more expensive solutions to keep it running smoothly.

trippertim wrote:For the most part unless it is a BSA68 / or BSA73 bottom bracket, it is a "press fit" bottom bracket. BB30, PF30, BBRight, 386 Evo, BB90 etc are all "Press Fit"

That said, even the Shimano and Mega Exo and GXP are press fit bearings, it is just the bearing is pressed into an assembly which is then threaded onto the bike instead of pressed into the bike.

I did not actually say that the Shimano/MegaExo were equivalent to the pressfit standards. I said they are press fits, just like almost every other bearing and bushing on most mid to high end bikes (wheels, freehubs, pedals, headsets)  I have not had a bottom bracket bearing on one of my primary bikes that was not press fit since the early 90’s.  If you are correct that the bike industry consider them to be different things (I know people in the bike industry that don’t), then that seems to me to more so be a reflection on the bike industry than the technology.

You bring up that there are more issues with bottom brackets that are pressed in. If the issue causing the creaking is the difficulty of getting bearing seats to the correct tolerances /spec’s and then the bearings installed in the application properly, then why do we not have more issues with wheels etc?

I would theorize (I don’t have the data so I won’t put my opinions forth as facts) that it has to do with either manufacturers not paying attention to the quality of their bearing seats or to the bearings they are buying, or with LBS’s (or people themselves) not properly installing them.

I’m not pretending they are the same, I’m saying that fundamentally they are the same. The mechanical difference between a bearing pressed into the threaded housing and a bearing pressed into the frame is the two extra threading steps per side. A properly pressed press fit bearing is a properly pressed press fit bearing. The value added steps that both systems include are machining the bearing seat, making sure the bottom bracket sides are aligned and pressing in the bearings. The additional steps that the threaded system has are threading the bottom bracket, threading the bearing ‘cups’, facing the bottom bracket and threading the assemblies into the bottom bracket. I do not see how these additional steps add value.

From the perspective of the whole system, the threaded housing can provide a little bit of ‘isolation’ between the bearing and the frame, but the additional housing of a PF30 also can provide this isolation. The threaded systems are also not immune from misalignment, manufacturing defects and wear. If you install and remove threaded bottom brackets multiple times, you can wear out the threads, and the threads can seize and/or gall. This system is more of a hold over from when bearings were loose and preload was adjusted with the threaded cups (see my pic above) than any sort of technical advantage / advancement.

My challenge to you would be to find me other applications where bearings are pressed into a housing and then those housings are threaded into the application. I’m sitting here wracking my brain trying to think of one and have not come up with one yet. (I might be missing something obvious though). Once you find one, I’ll be curious to see how relevant weight/stiffness is in that application.

My question is why are we buying expensive frames from companies that can not consistently execute a simple bearing seat or patronizing bike shops that can not properly install 6806 bearings which are probably made and pressed in hundreds of thousands of times around the world each year (first supplier I found for 6806 on Alibaba had a capacity of 1 million per month). If they can’t execute something this simple, I worry about the rest of their design / manufacturing / service skills. In our house we have bikes from multiple manufacturers with BB30, PF30, BBright and threaded bottom brackets. The only issue I have had with any of them was when I installed a used bearing that came with a used crank I bought. As I said in my earlier post, I’ve pressed in many bearings (mostly outside of cycling applications) and a PF30 or BB30 has to be one of the simplest I have done, but I am not a “mechanical idiot” (your phrase not mine).

I could ramble on and on, but I’ve already repeated most of the points made in the article you linked about it being an issue with execution and pressed bearings being a proven technology. When it is an issue of execution, it is the people executing it that need the blame, not general statements such as "threaded bottom brackets are superior". My apologies if you think I am calling you out / singling you out. This is just a topic where the general attitude of LBS's and many people who don't realize that all BB bearings are pressed causes people to make false attribution to where the problems actually lie.