How to: Bottom brackets

 

One of the frequently asked questions is, what type of bottom bracket do I need for my bike? To help you out, We have created this article with every information you need to know about bottom brackets(BB). We have 4 basic types of BB (Euro, Spanish, Mid, USA).

 

The bearings on the picture above are ordered from the smallest to largest - Euro size, Spanish size, Mid size and USA size. Notice that EURO and USA size bearings are both pressed in case. EURO and USA size bearings are not sold separately.


Before we dive into the detailed description of each BB type, let's have a look on what does marking SB or BB mean.
SB - Sealed Bearings: Quality sealed bearings
BB - Ball Bearings: unsealed bearings (less quality plus difficult maintenance). Nowadays the ball bearings are only used for some of the complete bikes for beginner riders.

 

CHOOSING OF THE CORRECT BOTTOM BRACKET

If you want to be sure about what type of bottom bracket you should get, then you will always have to know these 3 basic data.

1. Bottom bracket shell type: USA, MID, SPANISH, EURO. Each name stands for the different bearings size which only fits with frames that have the same bottom bracket shell.

2. Spindle diametter of your crankset: 19mm, 22mm or 24mm.

3. Bearings version: BB (ball bearings) or SB (sealed bearings)

TBB-BIKE marking example: "3457 WTP Mid size BB kit 19mm" // product number, manufacturer, type, kit=complete set (bearings, spacers etc..), spindle diameter.    

 

 


DIVIDING OF BOTTOM BRACKET BEARINGS BY SIZE

Bottom bracket shell inner diameter determines the bearings outter diameter size. There are 4 basic types of bottom brackets in BMX. The smallest one is Euro size (rarely used today), than Spanish size, Mid size and the largest one is USA size. It is safe to say that most used bottom bracket in bmx today is Mid size with the Spanish size on the second place.

 

 

EURO SIZE BB
Smallest one out of all other bottom brackets. EURO size bearings are pressed into the aluminium case with outter thread that is screwed into the bottom bracket shell. This type of BB is rarely used today as it was very deffective and difficult to maintain.

Marking example: 22x31x72xRS // ISK or 1905137 - 2RS // NBK

Description:
- diameter- 31mm
- width- 6,9mm
- inner thread- 1.370" x 24tp

 

SPANISH SIZE BB
Bottom bracket shell is more lightweight than Mid size. Bearings are pressed into the BB shell. It is mostly used by the companies producing frames of lowest possible weight (Fly bikes, Macneil..).

Marking example: 22379 - 2RS // NBK

Description:
- diameter - 37mm
- width - 9mm

 

MID SIZE BB
Most used bottom bracket in BMX. Stronger, more durable and a little heavier than the Spanish BB. Mid size bearings are pressed straight into the bottom bracket shell.

 

Marking example: R12 RSD 22

Description:
- diameter - 41,3mm
- width - 11mm

 

USA SIZE BB
Original BMX bottom bracket with bearings pressed into the steel case which is afterwards pressed into the BB shell. Nowadays it is not used anymore.

Marking example: R12 2RS // ISK

Description:
- diameter - 51,5mm
- bearings diameter - 41,3mm
- bearings width - 11mm

AND HOW DO YOU FIND OUT WHAT TYPE OF BB DO YOU HAVE?
It's simple, just google the type/model/name either of your frame or a complete bike and look for the description bellow. Everything you need is right there. If you are not able to find your frame/bike online, then take the ruler and measure all neccesery sizes to find out what type of BB you have (use the details above). Don't forget to check on the spindle size of your crank set so you know exactly what do you need.



GENERAL DESCRIPTION OF BOTTOM BRACKET
The BMX Bottom bracket is composed of the parts you can see at the picture below. It is recommended to always get the whole BB set instead of just replacing some parts.

 

 

HINTS FOR MONTAGE OF BOTTOM BRACKET
Montage of bottom bracket is not an easy task and if it's your first time doing it, then we recomend you to get some assistance.

 

- do everything with deliberation and patience
- lube well all of the parts ( bb shell, bearings, spindle, cranks, bolts..)
- easiest way to press the bearings into the BB shell is to put them straight on the hole, place a small wooden plank over and hit it with the hammer to press the bearing in.
- spacer tube has to fit tightly on both sides of the edge for BB bearings, otherwise the bearings will be destroyed within a short period of time
- for 48-groove splines you will need a crank arm remover


HOW TO INSTALL A MID BOTTOM BRACKET WITH JIM BAUER - TRANSWORLD RIDE BMX MAGAZINE


If you have any questions or ideas on how to improve this section, please let us know via our e-mail info@tbb-bike.cz

 



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