Bottom Bracket Topic - Threaded vs. Pressfit

[ben_travis]

This is a cross posed from Pinkbike: http://www.pinkbike.com/news/poll-press-fit-bottom-brackets.html. The formatting has gone a little to rat sh*t, but might be interesting to some.

The Specialzed Carbon Demo's threadless bottom bracket shell is an aluminum insert which doubles to house the swingarm bearings - both are press-fit types.

There is an on-going battle between bike makers, retailers and customers over press-fit vs threaded type bottom brackets, with a large number of riders and bike shops opting for threaded cups. Frame and bike makers, however, have been systematically switching to press-fit types and if the trend continues, it will only be one or three years before all production mountain bikes will be converted to threadless bottom brackets. Before all you Knights of the Royal Order of the Threaded Bottom Bracket draw your swords, please understand that technically, ALL bottom brackets are press-fit designs. The only physical difference is that the conventional BB's bearing is pressed into a cup, while Press-fit types. like the popular BB30, have their bearings pressed directly into the frame. After they are pressed or tightened into a functional bottom bracket, both systems operate in exactly the same way.

Niner specifies threads for its WFO 9 AM/enduro chassis and for all the frames in its lineup. Frame sales are a large part of the business and Niner insists that its bikes are cross-compatible among component makers and also user friendly.

Arguments in favor of threads are numerous, but only three are viable: Threaded cups can be serviced with simple wrenches that almost everyone owns; threaded cups allow component makers to have complete control over every moving part of the crankset from pedal to pedal; and finally, threaded type bottom brackets seldom creak, while at present, press-fit bottom brackets often creak.

There is a mechanical reason why seatposts, headsets and bottom brackets creak when they are stressed. When a smaller diameter tube is being held inside a larger-diameter tube, there is a significant difference between the stiffness of the larger and smaller members. When a bending moment is applied to the smaller tube, the smaller-diameter member flexes more than the larger-diameter one which is holding it. The smaller tube elongates slightly as it flexes and it slips inside the larger one. That microscopic movement causes the creaking noise. The slip can be exaggerated when a bearing is pressed between the two members, such as a bottom bracket, because flex in the bottom bracket axle is multiplied by the distance from the axle to the outer diameter of the bearing.

Because bicycles have a number of places where this situation can occur, and because cyclists in general are enflamed by any recurring squeak or rattle, designers have spent many sleepless nights figuring out ways to silence seatposts, hubs, pedals, headsets and yes, bottom brackets too.

Once assembled, the external-cup, 73-millimeter threaded bottom bracket (top) and the 92-millimeter press-fit type (below) are functionally the same and use the same size bearings. The Press-fit, design, however, offers more bearing support, it has fewer and less complicated parts, and it gives frame makers room to widen frame tubes or get creative with suspension components.

Those naive enough to believe that threaded bottom brackets emerged from the cycling industry's womb creak free would be dead wrong. One hundred years passed before bike makes got a handle on that one. Headsets creaked like baby toads until mountain bike designers ditched the threads and adopted oversized steerers.

There are strategies in place to silence bottom brackets. Some thread-in cups have Teflon liners which allow the bearings to rock silently. Some are glued in tightly with thread-locking material. Some makers, like Chris King, rely on precise manufacturing tolerances and insider secrets to ensure silence. There is also a theory that aluminum external threaded cups flex just enough to prevent slip between the shaft and the bearings and thus naturally prevent creaking at the source. The point is moot, however, because over time, natural selection has eliminated all the brands that made noisy thread-in bottom brackets.

Proponents of threads either ignore or forget that even a perfectly faced and threaded frame can require the skills of a safe cracker to get the cups started without cross-threading them.

It is easy to mess up the fine threads of an aluminum bottom bracket cup. Acros makes a tool which keeps the cup and frame aligned to avoid cross-threading expensive parts.

Anyone who has cross-threaded a cup the night before a race or ride can attest that it is game-over unless luck is on your side AND you have a sharp set of bottom bracket taps in your tool box.

Park Tool's press-fit bearing removal and replacement tools are simple to use and they get the job done in minutes - however, removing a threaded external cup with a spline wrench is a much more civilized process.

A large number of press-fit supporters come from the manufacturing sector because threading and facing frames is costly and bolloxed threads can be a significant manufacturing and warranty issue. Pressed-in bearings are simpler to install and replace, and press-in BBs are less costly. More important, though, is that carbon construction can produce a beautifully precise press-in interface, but it does not lend itself well to threads, so typically, a threaded-aluminum insert is bonded into the BB shell. Press-fit BB shells are made the full width of the bearings (92mm wide instead of 73mm) which also gives frame designers room to widen the frame tubes and make the BB area much more rigid. A number of home and shop tools now exist that make removing and replacing press-fit BB bearings a three-minute operation, and bearings can be purchased from any number of sources, including on-line industrial suppliers in any country. It would seem then, that the last real barrier to press-in is noise.

A bit of an exaggeration, but the bottom bracket area of Pivot's carbon Les Fat illustrates how much wider and more rigid the frame can be made when press-in type bearings are used.

One can extrapolate that it is only a matter of time when bike and component makers will silence press-fit bottom brackets. Shimano has made great strides by encasing the bearing in a press-in nylon cup (other BB makers are now using similar cups). The thermoplastic has just enough give to absorb any bearing movement, and also, it can overcome a slight amount of misalignment or out-of-roundness in the frame. Nylon also does not transmit sound well, so the cups act as a silencer, which is a key feature, especially when one considers how carbon frames tend to amplify sounds like musical instruments. Eliminating creaky press-fits can't be easy, otherwise it would have been done long ago, but "difficult" is not "impossible," .

Edited August 7, 2015 by ben_travis

[AndrewEH1]

The fact that I can easily, with one cheap tool, fit or remove a BB in about 2 minutes makes it the winner in my eyes.

If your excuse is that you mess the threads up then maybe you shouldn't be fixing your bike in the first place.

Edited August 7, 2015 by AndrewEH1

[aener]

Press-fit until I die.

Used to have lots of trouble with bearings dying in threaded BBs, but have had significantly less with press-fit.

Never had a creaky one either, though maybe that's just less of an issue for trials riding...

Sure, it's technically two tools, but removing and fitting a press-fit with a hammer and bearing press (Echo tool style) makes a two-minute job of those too.

In my mind, the less parts a bike has the better. Especially if that also means less threads.

Press-fit BBs, integrated headsets, integrated tensioners (Echo style) and the like are all good things, I reckon.

Through axles will also sit in that category when they use a separate threaded component (external nut or something) on one side. Threading frames/forks seems like a step backwards

[Scott Gibbs]

Could a threaded frame be milled or machined to take a press fit BB like the Echo one?

[FamilyBiker]

if you fk up an external bearing cup youll replace the bb and its fine again.if you fk up the bearing seats of a pressfit bb the frame is for the bin.

the whole pressfit shit is ust manufacturers lowering production costs.the 2 out of 50 bikes where it makes sense to go for it ( fat bikes,bmx,such things)dont justify it being THE new bb standard i think

just my 2.363ct

Edited August 8, 2015 by FamilyBiker

[aener]

Edit: I withdraw my effort to try and help people understand something so I don't get the blame for an argument pinned on me again.

Edited August 8, 2015 by aener

[Paperclip]

In my mind, the less parts a bike has the better. Especially if that also means less threads.

This, although I would like to see Echo or Trialtech make a axle and spacer (for between the bearings) so it's more like other systems.

[Mark W]

Yes and no - the only reason other setups use that axle spacer system is because there's no standardisation for pretty much anything in any discipline any more. If you know that your bearing seats are 48mm apart then having seats integrated onto the axle so you don't need to use a spacer is pretty handy.

[Alex Dark]

Press fit is a great idea in my opinion , if it works fine for headsets and even 10 year old frames that have had multiple headset changes are still going , then bottom brackets should be fine.

[FamilyBiker]

theres a difference between thinking that you understand something better than other people and trying to teach them an opinion, and knowing stuff for real because its your job to know such things.

without even knowing id say the post that quoted mine was going down that road.knowing the author is enough to say this

people normally have 2-5 bikes depending on how much they ride and spend.youll see 1 problem out of 10 pressfit setup bikes so as a customer you will see many.

as the workshop guy youll pay the price,because 1 out of 10 i9s 10 out of 100 bikes you sell,so its 10 pressfitt bbs you have to look after in the workshop because they creak,have play etc (whereas 9 out of 10 threaded bbs make it for the 2 years of warranty customers got)

thats 10 labour units your shop could use to earn money instead of working for free.

with threaded bbs we didnt have a fraction of the problems we have with bb30 and co,its just a fact.

now try and either write a book or write in lyric artistic style to say i aint right,or go and ask a workshop if i am,forum knights lol

Edited August 9, 2015 by FamilyBiker

[darkness]

Have no issues with threaded BBs for over 15 years.

[Luke Rainbird]

youll see 1 problem out of 10 pressfit setup bikes so as a customer you will not see many.

...(whereas 9 out of 10 threaded bbs make it for the 2 years of warranty customers got)

Sweet maths skills. 10%>10%?!

[Herbertlemon102]

Press-fit until I die.

Used to have lots of trouble with bearings dying in threaded BBs, but have had significantly less with press-fit.

Never had a creaky one either, though maybe that's just less of an issue for trials riding...

Sure, it's technically two tools, but removing and fitting a press-fit with a hammer and bearing press (Echo tool style) makes a two-minute job of those too.

In my mind, the less parts a bike has the better. Especially if that also means less threads.

Press-fit BBs, integrated headsets, integrated tensioners (Echo style) and the like are all good things, I reckon.

Through axles will also sit in that category when they use a separate threaded component (external nut or something) on one side. Threading frames/forks seems like a step backwards

i agree with this completely.

[gage-mann]

On a trials bike I wouldnt worry about messing up the area where the bearing seats when removing and reinstalling because one, trials frames usually break (crack) before the bbs big bearings break or axle break. Two it's called pressfit because it's presses in basically even when you tighten the crabks on so I don't see how you could mess it up and three all you need to take the bb out it a large hammer.

I don't see the problem if replacements are the same price as other bb options. People still mess up threaded bbs by cross threading them and ruining the alloy cups with the bb tool (these people are the ones that would manage to mess up installing a pressfit though)

[FamilyBiker]

Sweet maths skills. 10%>10%?!

haha typo,10 out of 10 pressfit produce problems over the same time where 9 out of 10 threaded ones dont,thats what it was supposed to be saying.

it just didnt type that 0 haha my laptops keyboard is fkd up,doesnt like y and j either

[Mark W]

Do any of those pressfit ones include the weird MTB standard (whatever it's called) where it's pressfit but has that plastic cup/sleeve type thing too?

[marko]

Could a threaded frame be milled or machined to take a press fit BB like the Echo one?

No. This would remove too much material... and the cups that are missing too, making it even weaker.

Edited August 10, 2015 by marko

[Mark W]

Yeah, the shoulder part of the bearing seat would probably become the weak point. You'd need to machine away 1.5mm of material out of the cup to match the outer diameter of the bearings, so the lip the bearings sit against would then be really shallow and wouldn't have that much support, especially as the seat would be within the threaded section of the shell.

[gage-mann]

Any body remember the dmr bottom bracket converter cups? That's screwed together in a bmx bb and you could thread a normal mtb bb in? Just need something like that to sit inside a 68mm frame but obviously allowing for spacing for a bearing either side?

Maybe threaded shims (like bb cups already) that seat bearings either side perfectly? The cups would have to have a tool to screw them in though. Plus getting the sizing right for it all could be a major hassle.

[Ash-Kennard]

I personally won't be using Pressfit BB if I can help it. I remember working in halfords and replacing BB bearings constantly on the BB30-90 bikes. Much rarer to have to replace a std threaded BB for some reason.

There are some significant weight benefits for trials, but a creaky bike would piss me off no end.