The humble bottom bracket has changed a lot in recent years, so let’s take a look at all the new systems and see what makes them tick.
The bottom bracket forms the interface between your bike frame and the cranks. When functioning as intended it’s easily forgotten. However the bearings and related fittings live in a relatively dirty and potentially moist environment. When the need for maintenance comes around, it’s handy to know what’s inside.
For decades the bottom bracket standards found on road bikes were just that; relatively standard. Yes, there have always been a few left-of-centre systems but through the 80s, 90s up until the early ‘noughties’, the vast majority of road bikes relied on the English or ‘BSA’ bottom bracket standard. Some frames would require an Italian bottom bracket and more recently you’d see the occasional BB30 system, but that was about it for the mainstream brands.
Nowadays the threaded English bottom bracket lives on but it’s nowhere near as popular—in fact this once dominant standard is now in the minority on new model upper-end road bikes. Adding to the mix we now have a Press-Fit BB86, BB90, BB30, Press-Fit 30, BBright and BB386 EVO.
Your bottom bracket system is determined by the bike frame and manufacturers usually tie their allegiance to a particular standard, touting the advantages of whatever system they choose. The manufacturer’s choice will influence how you go about servicing the bottom bracket and it may also impact your choice of cranks. What follows is a rundown of the features, benefits and idiosyncrasies of the current day bottom bracket systems.
English, Threaded or BSA
If you’ve been tinkering with bikes for a few years, there’s a good chance you’ll be familiar with the English/BSA standard. To fit this system a frame needs a 1.37 x 24 TPI thread on the inside of the bottom bracket shell. The inner diameter is roughly 34mm and for road bikes the shell is 68mm wide (the mountain bike version uses a 73mm wide shell).
A little background on this ‘old-school standard’ will help to explain how bottom brackets have evolved and why we now see so many new systems popping up. Go back around 20 years and most good quality cranks relied on a square tapered interface to connect the arms to the bottom bracket spindle. The spindle itself was usually 17mm in diameter. This is comparatively thin by modern-day standards and the skinny spindle left plenty of room for bearings between it and the bottom bracket shell.
While this design was good for bearing longevity, the square taper interface between the crank and spindle tended to be problematic. You’d often encounter tolerance issues and the taper itself would change over time, allowing the cranks to slide on too far. The skinny 17mm shaft found on most square tapered spindles also stood as a limiting factor for those looking to improve the stiffness-to-weight ratio in this area. To obtain sufficient strength, the spindle was usually made from chrome-moly steel with very stout walls, and many spindles were solid steel all the way through. While this did the job, even under powerful sprinters, it didn’t do the bottom bracket any favours in the weight department.
These limitations saw Shimano introduce their patented Octalink system, which was followed by the open standard called ISIS (International Splined Interface Standard). Both of these systems employed a larger 19mm diameter spindle and the splined interface gave better consistency when mounting the cranks. While the 19mm spindles were theoretically stiffer without the weight penalty, the bearing size was reduced and this impacted on the longevity of many bottom brackets from this generation.
This desire to place larger spindles within the English bottom bracket shell lead to the next big shift; the move to external bearings. Alloy cups thread into the frame and position the bearings outboard from the bottom bracket shell. This design allows for a much larger 24mm spindle without limiting the bearing size. The wider stance of the bearings also supports the spindle closer to the crank arms, offering better support against pedalling loads—at least in theory anyway.
Most crank manufacturers adopted the 24mm spindle external bearing system, including Shimano, SRAM, Campagnolo, FSA and plenty of others. This popularity means you’ll have a good selection of cranks at your disposal if your bike has a threaded English bottom bracket shell.
Moving to an oversized system has allowed crank manufacturers to make their products lighter and stiffer, employing everything from thin-walled chrome-moly to aluminium and even titanium for the spindle itself.
Retaining the threaded design of the traditional English bottom bracket makes this system quite user-friendly—it’s certainly easier to service than some of the newer designs. The bearing assembly can be removed and re-fitted as desired with comparatively inexpensive tools—there’s definitely no need to attack your bike with a hammer! There’s also scope to make small changes to the bottom bracket spacing if you need to customise the chainline or shift the crank placement within the frame.
Bigger 24mm spindles are now the norm with threaded external cups but some special bottom bracket fittings will even allow a 30mm diameter spindle to pass through a regular threaded English bottom bracket shell. However one thing that can’t be avoided with external bearings is added width. Back when the bearings were housed within the 68mm wide frame, cranks could sweep inboard towards the narrow shell and offer more ankle clearance. With the internal system there was also the potential to achieve narrower spacing between the pedals (known as the Q-factor), although this measurement is also restricted by other factors such as the chainstay width.
While better ankle clearance is usually a good thing (especially if you pedal with duck-feet), the narrower pedal stance or Q-factor is more of an individual matter. Some people may find it better to pedal with their feet closer together while others may not.
The main drawback of the old English system lies with the added complexity in the production process. Threading the inside of the frame adds another manufacturing step and the outer faces of the shell need to be parallel and perfectly machined. A poorly finished bottom bracket shell is likely to lead to a creaky and unreliable bike.
Press-Fit BB86 (Scott, Giant, Avanti and many others)
Now we’ve outlined the old-school bottom bracket system, let’s move onto the newer designs. First up we’ll look at BB86, as it’s closely tied to the English bottom bracket with threaded cups.
Both systems are made to suit the common 24mm crank spindle, but instead of using threaded cups that protrude from each side to hold the bearings, a BB86 frame is made wider so the bearings can be housed within the shell. With BB86 there’s no thread within the bottom bracket shell. Instead the bearings are housed within a nylon casing that is pressed into the frame.
The ‘86’ in the name refers to the width of the frame but it measures 90mm across once the nylon shell is pressed in; that’s exactly the same as a threaded English system with the external cups fitted. As a result, it fits a wide range of 24mm spindle cranks from Shimano, FSA, SRAM and others.
Until recently you couldn’t fit a 30mm crank spindle to a frame that used the BB86 system but now there are some bottom brackets that allow the fatter diameter spindle to work (FSA and Rotor make them and there may be others). These won’t allow you to fit a dedicated BB30 crank, as the spindle will be too short, but wide spindle 30mm cranks that cater for a 90mm bottom bracket width can work (Rotor 3D and FSA BB386EVO cranks for example).
Stiffness is the main advantage touted by manufacturers using the BB86 system. The cranks don’t change but the wider span of the bottom bracket shell allows for a broader down tube, and this stands to improve frame stiffness. It can also trim a few extra grams from a carbon frame, as you no longer need metal threads to fit the bottom bracket—it can slip straight into the carbon frame. As a side benefit, this also removes a potential failure point because there’s one less bonded junction.
The nylon housing of the press-fit bottom bracket compensates for small imperfections within the frame shell, so manufacturing tolerances don’t need to be as precise and there’s no need to tread the inside of the shell. As a result the BB86 is easier and cheaper to produce, and this makes it attractive to the manufacturers. The use of a nylon shell also reduces the likelihood of creaks developing; something that’s arguably more prominent with press-fit designs (although a poorly faced threaded bottom bracket is just as likely to be creak-prone).
While BB86 theoretically leads to a stiffer and marginally lighter frame, the main drawbacks lie with its serviceability. The old-school threaded standard allows you to remove the bottom bracket cups with commonly available and inexpensive tools. With BB86, removing the bottom bracket can damage the press-fit nylon cups, forcing you to purchase a new bottom bracket to get the bike back on the road. Destroying the bottom bracket isn’t a big deal if the bearings are already flogged out, but what if you’re searching for one of those ‘mystery creaks’ and want to remove and refit the bottom bracket with a little extra grease? It’s probably not a deal breaker when choosing a new bike but it’s a point worth considering if you like working on your own bike.
The BB90 system also ties closely to the threaded cup, external bearing English bottom bracket and offers compatibility with most 24mm spindle cranks. It originally came out on the Trek Madone and is mainly found on Trek bicycles. The ‘90’ refers to the width of the bottom bracket with the bearings fitted; again this is identical to a threaded English system with the external cups fitted.
The prime difference between BB90 and BB86 is that there’s no nylon shell with the Trek designed system; the bearings slip directly into the frame. While the bearings have a snug fit within the frame, you don’t need specialist tools to fit or remove them. This makes it more user serviceable than the nylon cup equipped BB86 system. While Trek sell their own service kits to suit, there’s nothing to stop you sourcing your own replacement sealed bearings from a bearing shop (this can be helpful when you don’t have a bike shop close by).
So BB90 is easier to service than press-fit BB86 but it still allows the manufacturer to make a very wide bottom bracket assembly and inflate the size of their frame tubes for added stiffness. Manufacturing tolerances need to be spot on with BB90 as there’s no nylon shell to compensate for misalignment. The only real limitation with BB90 lies with crank compatibility; it’ll only work with 24mm spindle cranks and there’s currently no way of fitting a crank that uses a 30mm spindle.
BB30 (Cannondale, Apollo, Felt and many others)
Back in 2000 when many brands were playing with the idea of a larger diameter bottom bracket spindle, tiptoeing around with the 19mm Octalink and ISIS designs, Cannondale threw existing standards out the window and created BB30.
BB30 employs a larger diameter shell (46mm internally versus 34mm on a threaded BSA shell), which allows them to run a fat 30mm spindle with plenty of room for large bearings.
The fat axle lets the crank manufacturer use an alloy spindle to drop weight whilst retaining plenty of stiffness. Some exotic brands have even dabbled with carbon fibre spindles to further push the stiffness-to-weight boundaries. The extra room provided by the larger diameter BB30 standard has certainly allowed crank makers to get more creative.
While the BB30 system is substantially fatter than the longstanding threaded English design, it isn’t any wider. The outer width remains at 68mm for road bikes (73mm on MTBs). This presents both pros and cons; BB30 cranks can curve in to offer more ankle clearance and there’s potential to gain a lower Q-factor, which may be advantageous for some riders. When compared to the BB86 system, the narrower shell doesn’t offer the same ability to expand the width of the down tube (if the manufacturer feels this is necessary).
With BB30, the bearings press directly into the frame, so the manufacturer needs to adhere to precise tolerances. As a press-fit system, there may be a greater tendency to develop creaks, although much of this will come down to proper instillation of the parts and the bottom bracket shell meeting the required tolerances. BB30 bearings have a tight fit within the frame; while it may be possible to remove and refit the bottom bracket by improvised means, it really should be done with the proper tools, and these usually aren’t cheap.
While BB30 was designed to use a 30mm spindle, you’ll find a wide range of adaptors that allow you to use 24mm spindle cranksets, so cross-compatibility is good with this system.
Press-Fit 30 (used by a broad range of manufacturers)
While BB30 lets crank manufacturers get creative with fatter spindles and lots of ankle clearance, the direct mounted bottom bracket bearings mean that the frame manufacturer really needs to be on the ball with their bottom bracket tolerances.
Press-fit 30 (PF30) also fits a 30mm spindle with big bearings, but the inner diameter of the shell increases from 42mm on BB30 up to 46mm. The larger inner diameter makes space for a carrier, so the bearings don’t sit directly into the frame. Using a nylon housing for the bearings provides a broader margin for error and makes the job easier for the frame in manufacturer. Beyond that it functions just like BB30 and fits the same cranks, so expect to find good ankle clearance and lower Q-factors with some cranksets.
Servicing PF30 is similar to dealing with the smaller diameter BB86 system. Both run pressed-in nylon cups that are prone to damage when removed from the frame.
As with BB30, the PF30 system can fit most 24mm spindle cranks. This is either done with an adaptor-style bottom bracket or by fitting reducers to the spindle.
Over the years Specialized has employed a couple of different versions of their OSBB system. It ties very closely with the BB30 and PF30 systems. The ‘Alloy OSBB’ system places the bearings directly into the 42mm diameter of the bottom bracket shell, while the ‘Carbon OSBB’ runs pressed-in cups and a 46mm inner-diameter bottom bracket. Alloy OSBB is cross-compatible with BB30 and the Carbon OSBB is basically the same as PF30.
BB386 EVO (BH Bikes, Wilier, Litespeed and FSA)
BB386 takes the massive 46mm outer bearing diameter of the PF30 system and combines it with the broad external width of the BB86 design. The added width lets frame manufacturers increase the size of their down tube while the big inner diameter makes way for a fat but light 30mm crank spindle.
A dedicated BB386 system (as found on some BH bikes for example) will run a wide press-fit bottom bracket with the bearings housed inside nylon cups. With this you’ll need dedicated tools and presses for assembly and encounter the same servicing issues as found with the PF30 and BB86 setups.
One of the neatest features of BB386 is the cross-compatibility that it offers. You don’t need a dedicated frame to fit the large diameter spindle of the BB386 cranks. Bottom brackets are made that will squeeze the 30mm spindle into a threaded BSA frame or a BB86 equipped bike. As it shares the same 30mm spindle as a BB30 or PF30 bottom bracket, it’ll also work with them (you just need to add spacers to compensate for the added spindle length). About the only system BB386 cranks won’t work with is Trek’s BB90.
BBright is a bottom bracket standard developed by Cervelo that uses a 30mm axle and press-in bearings. In many ways it’s similar to the PF30 system except the bottom bracket is asymmetric, with the non-drive side (LH) bearing placed 11mm further out from the centre line of the frame. This is done to allow the frame manufacturer to create a wider down tube and a larger left-side chainstay. Once again increased stiffness is the goal. Why not just make the bottom bracket wider on both sides like BB386? A wider shell on the drive-side results in a more elaborate profile on the spider to get the chainrings in the correct spot. The offset design of BBright lets the frame designer gain larger frame dimensions on the left-side with a more simplistic and theoretically stiffer crank profile on the drive-side. Once again, BBright relies on press-fit cups, so it’s very similar to PF30 and BB86 in regards to its serviceability.
And the Winner is…
Each manufacturer touts their bottom bracket system as being the best but in reality every design has its relative strengths and weaknesses. Threaded bottom brackets are generally the easiest to service but some press-fit systems can produce a lighter/stiffer frame by eliminating bonded-in metal parts. Look at the crankset weights too as some of the 30mm spindle cranks are a good deal lighter than their 24mm counterparts. Consider the features you want and choose accordingly, or just go with the bike that you like best and live with whatever crank/bottom bracket system it comes with—that’s how most of us do it!
It’s also worth stating that the quality of finish and construction makes a big difference with any bottom bracket/frame combination. Press-fit systems can creak but this shouldn’t be an issue on a well finished frame that’s been assembled correctly—both the frame and the bottom bracket tolerances can have a bearing on this. A traditional bottom bracket is just as likely to produce noise if the frame is poorly faced, or if the threads aren’t greased and tightened properly.
So there you have it. Bottom brackets have certainly changed in recent years and hopefully this refresher now has you up to speed with all of the current systems—at least until the next new bottom bracket ‘standard’ is launched!
So what’s really inside your bottom bracket and what tools are required to pull it apart? Here’s a peek inside two of the more popular bottom bracket systems; BSA/English and press-fit BB86.
To start with, the cranks have to be removed so you’ll need the tools specific to your crankset. Some use a couple of pinch bolts with a splined spindle (like the Shimano ones pictured), while others use a press-fit spline and a self-extracting bolt (most SRAM and FSA models). Check with the crank manufacturer’s instructions if you are unsure of this step.
With Shimano cranks you’ll need to remove the bearing preload cap with a suitable tool—these are relatively cheap and commonly available.
There’s a small plastic tab that sits in the split where the crank bolts cinch down on the spindle; use a small flat screwdriver to pop this up. The crank won’t come off until this is done.
Now the cranks will slide out through the right hand side. If it’s tight, give the left side of the spindle a tap with a soft hammer.
Use a bottom bracket spline spanner to undo the threaded cups. The left or non-drive side uses a regular thread (anti-clockwise to undo) while the drive side is a reverse thread (clockwise to undo). Most bottom brackets will have marks that show which direction you need to turn them.
Thoroughly clean the inside of the shell and apply a film of grease to the thread before you refit the cups. Dry or loose bottom bracket threads are a prime cause of noise in this area. If you’ve got a titanium frame, consider using anti-seize.
Refit the bottom bracket cups and tighten. Use a torque wrench if you have one (35-55NM) or just make the cups ‘nice and tight’ without giving yourself a hernia.
Slip the crank back through, push in the plastic safety clip and gently nip up the bearing preload the using the end-cap. Don’t get overzealous with this or you’ll speed the bearing wear. Nip up the pinch bolts and you’re done!
To work on a BB86 you’ll need a cup removal tool (pricing ranges from around $50 through to $140 for the genuine Shimano item) and a bearing press to put the new cups back in (similar pricing to the removal tool). Improvising with other tools can make the job harder or damage the bike if you’re not careful.
The initial steps are the same as the threaded system, so we’ll skip to this point. With the cranks removed, pass the extractor tool through one side until it reaches the bearing on the opposing side. Now spread the head of the tool so it locks securely into the bearing.
Give the end of the tool a good solid hit with a hammer to dislodge the cup—in some cases this will take a good deal of force. Once it starts to creep out, tap gently and place your hand over the cup to catch it. Repeat with the opposite side and you’re done.
This Avanti is an example of a frame with no alloy insert—the bottom bracket simply presses into the carbon shell. It’s generally recommended that you renew the bottom bracket once it’s removed. Hammering it out by the inner race can damage the bearing or destroy the nylon shell. While that is the ‘official line’, we feel that these bottom brackets can be reused in cases where they press out with minimal force. If the bearings remain smooth and there’s no damage to the cups, you may want to give it a go.
Thoroughly clean inside the frame and you’ll be ready to reassemble. While the nylon cups mean that grease isn’t essential, we like to smear a film of waterproof ‘carbon friendly’ grease on the press-fit surfaces before instillation. Place the cups in the frame and use the threaded press to wind the bearings in. Make sure the cups go in straight and press them firmly home. Refit the cranks and you’ll be ready to roll.