What size bottom bracket should i buy

The spindle is attached to one or both crank arms. The bottom bracket bearings are components on your road bike or mountain bike that wear out. In fact, some of the standards can be interchanged without issues. So what bottom bracket bearings fit what bottom bracket shell then? This extensive how to on replacing your bottom bracket bearings is divided up into a number of simple steps. We start with taking a look at how you can determine whether your bottom bracket bearings need replacing.

They allow you to combine various different standards. Creaking, squeaking, or play or a rough feeling as you pedal are all indicative of the bottom bracket bearings requiring a thorough check. It could also be that you want to give your bike a nice upgrade. If you notice they start to wear, you could see whether you could do with just replacing the bottom bracket bearings.

You can check by firmly grabbing onto the crank arm and trying to wrench it from side to side. Do you feel or see any play? Then at the very least your bearings will need replacing.

Identifying your bottom bracket shell can be quite a hassle. Below is a list of bottom brackets and how you can recognise them.

Both the outside and inside of the shell can have codes on them that make identifying the shell a lot easier. If you have a pair of calipers then you might want to have these at hand as well. The BSA and Italian thread bottom bracket shells are predominantly something you find on bikes made before These two types of bottom brackets are the so-called threaded bottom brackets, which feature a thread on both sides of the shell.

A frame with a BSA fit is incredibly commonplace. There are 4 widths available with BSA bottom brackets; 68mm, 73mm, 83mm or mm. For road bikes, a BSA bottom bracket is always 68 mm wide.

Other sizes, and particularly the 73 mm width, is commonplace with mountain bikes. The 83 mm and mm dimensions have become rare these days. A BSA bottom bracket can also be recognised by the writing on the bracket itself. The bearings denote: 1. This means that the diameter of the thread is 1. The diameter of a BSA bracket is between The thread on the left side non-drive side is a regular thread. You turn it clockwise to lock it. The right part drive side is a reverse thread and has to be done up counter clockwise.

A BSA equipped frame can be fitted with almost all types of cranks. The width is always 70 mm. Furthermore, and this is where it stands out, you always have to do up both sides of the bracket to the right. Thus the name Italian Thread. The downside is that the right cup is prone to coming undone more easily. This is precisely why you see these bottom brackets less and less on modern bikes. The most important mark on the bottom bracket is 36 x This means that the diameter of the thread is 36 mm and the thread turns 24 times per inch.

BB30 bottom brackets have been used frequently since The spindle always has a diameter of 30mm. This ensures a low weight and lots of stiffness. The bearings in the bottom bracket shells are pressed directly into the carbon or aluminum of the bottom bracket. This is a precision task though. Also a worn out BB30 Bracket easily shows play and starts to make creaking noises.

Therefore the BB30 is being used less and less frequently. The width of a BB30 bottom bracket is 68mm or 73mm. With mountain bikes, 68mm is most common too, but sometimes the wider version with 73mm width can be found. The diameter of the bottom bracket is If you want to use a Shimano crank, you need an adapter or a bottom bracket bearing which is placed in a special bearing tube. This also prevents creaking sounds.

From the outside, you actually barely see the bottom bracket bearings. BB30A bottom brackets are exclusively used for Cannondale road bikes. The difference between these and a normal BB30 is the diameter of the bottom bracket, which is 42mm for the BB30A instead of The width is always 73mm.

This is a frequently used standard for both road bikes and mountain bikes. The bearings are not placed directly in the frame, but instead they lie in an aluminium or plastic shell which is pressed into the frame. This is a big advantage when it comes to wear and tear. As the bearings sit almost entirely inside the frame, the characteristics that you can see from the outside are limited.

Only a narrow edge is visible. On a road bike, this bottom bracket always has a width of This is where the name comes from too.

With mountain bike frames this bracket type is The diameter of the bottom bracket in the frame is 41mm. This is based on the BB30 Bottom Bracket. The quick creaking common with BB30 is not a problem with PF30 because the bearing shells balance play a lot better. To provide space for the plastic bearing shells, PF30 bottom brackets have a diameter of 46mm compared to 42mm for a BB The advantage is that PF30 bottom bracket bearings are compatible with BB30 cranks.

Additionally they are way easier to mount. The width of a PF30 is 68mm on road bikes and 73 mm on mountain bikes. From the outside, you only see a narrow plastic edge.

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By using our site, you agree to our cookie policy. Cookie Settings. Learn why people trust wikiHow. Download Article Explore this Article methods. Tips and Warnings. Things You'll Need. Related Articles. Method 1. All rights reserved. This image may not be used by other entities without the express written consent of wikiHow, Inc. Unscrew the bolt or nut in the middle of the crankshaft. Flip your bike upside down or put it on a bike stand.

Inspect the crankshaft, which is the big gear on one side of your pedals, to find how the pedal is connected to the crank. Get a socket wrench or screwdriver that fits the nut or bolt. Unscrew this piece by turning your tool counterclockwise and set it aside.

If there is a piece of plastic sitting on top of this nut or bolt, pop it off with a flathead screwdriver. This is the dust cap. Hold the pedal arm in place while doing this to keep it from turning. Screw the crank extractor tool into the bolt in the middle of the crankshaft. Under the first nut or bolt, there will be a bolt locking the crankshaft in place. Using the threaded side of your crank extractor tool, slide your crank extractor into the opening in the crankshaft and turn it clockwise to tighten it in the threading, if necessary.

On these bikes, you can simply push the crank extractor tool into the opening and wrap it around the bolt. Tighten the socket on the open end of the crank extractor tool. With the tool attached to the nut inside of the crankshaft, turn the socket at the end of the tool clockwise by hand. Once you determine your bottom bracket standard, you then need to Identify Your Crankset. BB Standard. Common Shell Width. Frame BB Shell Threaded? Also Known As. Wheels Mfg Bottom Brackets.

But, can also use GXP cranks in these. Some brands call this PF41, describing the frame shell diameter instead of the crank spindle diameter. May use removable c-clips as bearing stops, or the bottom bracket shell may have molded or machined bearing stops.

BB shell is 83mm wide, but symetrical. Aluminum cups are threaded into the frame that result in the BB86 standard 41mm ID x Little used threaded BB shell standard. Usually found on Cyclops indoor bikes. To accurately identify your frame's BB shell, always measure the ID and width. Or, have a professional bike mechanic do the work for you. You cannot use a facing or cutting tool that I know of in a carbon shell.

To make matters even more confusing, there exists a number of other threaded bottom bracket standards. Trek introduced the proprietary BB90 standard in on the revamped Madone and soon followed with the mountain bike-specific BB Instead of bearing pressed into aluminium cups that were then threaded into the frame, Trek pressed the bearings directly into the frame.

Bearing seats were moulded into the carbon frame structure to save weight, and bottom bracket shell width ballooned to 90mm on road bikes and 95mm on mountain bikes, creating more real estate for frame tubes and suspension pivots. Effectively, the space previously taken up by the bearing cups can now be used as frame real-estate, allowing larger and stiffer tubes to be used.

It also provides a simplified installation process. Crankset compatibility is thus unchanged, although you do lose the ability to run chain guides that sandwich between the driveside cup and frame. This system is not without its issues however, with shells becoming oversized due to wear being a relatively common problem leading Trek to release the very slightly oversized V2 bearings to compensate.

Perhaps partly due to these issues, Trek has, in fact, recently abandoned this bottom bracket standard on its Domane endurance road bike platform for , in favour of the T47 threaded standard.

It will be interesting to see if this trend carries over to future models in its range. We can do this without creating our own crank spindle standard because it adheres to the same spindle that a threaded BB uses. None that I can see. The road standard has an A number of other shell widths may also exist, though they all use the same bearing cups.

More recently, bearings have shown up that allow a 30mm spindle to be used. The dimensional restriction mean the bearings are generally quite small, as the system was designed around 24mm spindles. This can lead to reduced bearing lifetimes. This system has a number of different names depending on who you talk to. The key benefits are lighter weights owing to the larger, 30mm-diameter aluminium spindle and the elimination of separate bearing cups.

Plus, because the shell is still just 68mm wide, the cranks can also be made to provide more heel clearance — or, depending on the crank design, an even a narrower stance width commonly referred to as Q factor. By comparison, Dura-Ace weighs around g [we recorded g in our review — ed]. In addition to weight, another BB30 advantage is stiffness. By increasing the spindle diameter, you increase its resistance to twisting, which is where the bulk of the deflection in a crankset comes from.

Moreover, with the notable exception of Felt , which uses a carbon tube, BB30 also usually employs an alloy shell insert that has to be bonded or co-moulded into an otherwise carbon frame.

According to Cannondale, this allows for wider bearing spacing and better spindle support which should improve bearing longevity.