How To Measure Road Bike Bottom Bracket

There are a few different widths. Perhaps partly due to these issues trek has in fact recently abandoned this bottom bracket standard on its domane endurance road bike platform for 2020 in favour of the t47 threaded standard. Lastly cartridge bottom bracket is an older standard that features a small diameter internal and axle bearings sealed in a metal cylinder that screws into the bottom bracket shell as a single unit.

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I plan to get a shimano un26 but i note that there are a number of different sizes the sizes seem to be expressed as 68 110 where 68 is the shell width and the second number varies according to the table below from shimano s tech specs.

How to measure road bike bottom bracket. While the predecessors of this design obliged precise bearing adjustment with the use of two spanners cartridge bottom brackets became famous as fit and forget solution. Bottom brackets connect to the bike using cups that attach to the threading in the bracket s shell which holds the crank arms against the frame of the bike while allowing them to turn smoothly and safely. A square taper bottom bracket in the form of a cartridge is a reliable bottom bracket for your bike easy to maintain and replace in the event that you do need to replace your bb following the steps outlined here will ensure you get it right. Finally the bottom bracket height is the distance from the ground to the centre of the bottom bracket shell.

To measure rear chainline the easiest way is to measure the distance from the inside of the rear fork end or the outside of the axle locknut to the middle of the sprocket. What size bottom bracket fits your bike. Multiple spacers are included in order to fit both sizes meaning if you see a bb for sale that says 68 73 it means it will fit both but it includes a couple spacers in the box to make it fit the 68 those spacers or fewer of them are not needed if the shell is 73mm wide. This video shows you how to measure a bike bottom bracket so that you buy the right size bottom bracket for your bicycle.

So that s quite easy to measure although be careful to keep your bike straight. I need to replace the bottom bracket bearing on my fixie. Most road bikes that use a threaded bottom bracket measure 68mm wide and most cross country trail mountain bikes measure 73mm. Double this subtract it from the over lock nut dimension of the hub or the frame spacing which should be the same then divide the result in half and you have the rear chainline.

The 4 sided tapered bottom bracket spindles come in a variety of widths depending on the bike type and number of front chainrings so it s important to measure the old one if you re doing this. A bottom bracket refers to the cylindrical axle assembly that connects your pedal s crank arms to your bike. For maximum benefit do check out the video we made on the subject.