How Do I Measure A Bicycle Bottom Bracket?

To find out the size of bottom bracket needed,

measure the inside of the bottom bracket shell in your frame

, it will be 73mm, 70mm or 68mm. Some older frames may have Italian threaded bottom brackets, instead of the more modern English.

How do you measure a bottom bracket on a bike?

How do I know what size crankset to buy?

Crank length is measured from the centre of the bottom bracket axle to the centre of the pedal axle. If you’re not sure what length the cranks on your bike are, the quickest way of finding out is typically to just

look at the backside of your cranks, just below the pedal axle

.

Can I use a 68mm bottom bracket in a 73mm shell?

You could install it, but it will shift your chainline, shift the centerline of your feet, clearance issues might arise on the non-drive side, and you might be leaving some BB shell threads exposed on the non-drive side as well.

Are all bottom brackets the same diameter?

Threaded bottom brackets shells have been made over time in various thread standards that are not interchangeable. The common threaded bottom bracket uses cups or adaptors with the thread specification of 1.37′′ x 24 threads per inch (

approximately 34.8mm diameter

).

How do I know if I need to replace my bottom bracket?

To check if your BB needs replacing,

drop the chain off of the smallest chainring and spin the cranks. If there’s a side-to-side wobble, or feeling of grittiness, it’s time for a new one

.

What do the numbers on a bottom bracket mean?

The 68mm and 73mm dimension measure the width of the bottom bracket on the frame of the bike with no BB installed, simply the width of the shell

. Most road bikes that use a threaded bottom bracket measure 68mm wide and most cross country/trail mountain bikes measure 73mm.

Are bicycle cranks interchangeable?

Most bicycle cranksets are designed with replaceable chainrings

, so you can easily and more affordably swap the rings without having to replace your entire crankset. If your crankset is still in good shape, you may only have to swap your chainrings the next time you do your drivetrain maintenance.

Are bike cranks universal?

Cranksets at a glance:

Chainset choice is determined not only by the type of bike you are riding –

BMX, MTB and road chainsets are not interchangeable

– but also by the type of riding you prefer.

How do you measure a crank on a road bike?

The crank length represents the distance between the centre of the bottom bracket and the centre of the pedal axis

. The most common lengths are 170, 172.5 and 175 mm, but it is possible to find cranks between 165 and 180 mm in the market.

What is a 68 73 bottom bracket?

68mm is the bottom bracket shell width. 118mm is the spindle width

. Many external bottom brackets are compatible with both 68mm and 73mm shell widths. They’ll usually include spacers with diagrams telling you which spacers to use and where, depending on which BB shell width you have.

What is a T47 bottom bracket shell?

The T47 standard is essentially

a PressFit 30 shell with threads

. The internal diameter of a PressFit 30 bottom bracket shell is 46mm. A T47 shell has an thread diameter of 47mm with 1mm threads mated to a bottom bracket with an outside thread diameter of 46mm with 1mm threads.

Are all bottom brackets 68mm?

On road bikes, it’s always 68mm

. 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 41.96mm, and the bottom bracket bearings are always pressed into the frame separately.

How do you replace a bottom bracket?

Are all bicycle crank bearings the same size?

While modern road cranks are compatible with many different types of bottom bracket shells, some combinations are better than others.

Shimano (left) and GXP (right) crank axles share the same diameter — 24mm

— however the end of each axle is quite distinct.

How long should a bicycle bottom bracket last?

Simple rule is (unless you’re starting a long trip) “if it ain’t broke don’t fix it”. Do normal maintenance, keep things properly lubed and your BB should last for another

4,000 miles or more

.

How often should bottom bracket be replaced?

When To Service Your Bottom Bracket:

At the very minimum, I do it about each season change, but normally more.

Every three months

or so I’ll take the cranks out and if it’s a threaded bb, I’ll remove the bb and do the full service.

How do you change a Shimano bottom bracket?

How do I identify my Shimano bottom bracket?

How do I know if my bottom bracket is Italian or English?

The key difference is in how the two thread into the bottom bracket shell

. Like pedals, one side of a BSA standard bottom bracket shell is reverse (left) threaded, while both sides of an Italian standard bottom bracket shell are regularly (right) threaded.

What’s the bottom bracket on a bicycle?

What is a bottom bracket? Your bottom bracket

connects your cranks to your bike in such a way that they can rotate freely as you pedal and put power into the drivetrain

. It is located in the bottom bracket shell which is where your frame’s down tube, seat tube and chain stays all come together.

Does any crankset fit any bottom bracket?

DUB is compatible with BSA threaded, PF86, PF92, BB30 (73mm shell) and PF30 (73mm shell) bottom brackets and

cranksets are completely interchangeable between the different standards

.

How do you measure a crank arm on a bike?

Are one piece cranks interchangeable?

Virtually all one-piece-crank chainwheels are interchangeable

. They have a 15/16′′ hole in the middle, and another, smaller hole for the drive pin of the right crank to engage. You can buy single chainwheels of various sizes, usually for 1/8′′ chain, or double or triple chainwheels for 3/32′′ chain.