Converting a single-speed BMX bike to a multi-speed hub is extremely difficult and should not be attempted without the supervision of an adult with bicycle mechanical knowledge. Because of the mechanical limitations of a BMX bicycle, there is only one readily available way to perform this task, and it may cause premature bicycle frame failure. Typical internally geared hubs have from three to nine gears.
- Skill level:
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Things you need
- 20-inch rear wheel with an internally geared hub
- 10-inch adjustable wrench
- Metric measuring device at least 135mm long
- Mechanical (non-hydraulic) car jack
Obtain a 20-inch rear wheel with an internally geared hub from the local bicycle shop.
Use the adjustable wrench to loosen the axle nuts on the single-speed wheel installed on the BMX bike by turning them counter-clockwise.
Push the wheel forward in the frame dropouts to achieve chain slack and lift the chain off the drive cog.
Remove the wheel by carefully keeping the chain from snagging on the axle or drive cog.
Insert the auto jack between dropouts and expand jack until snug.
Expand the auto jack in quarter-turn increments. Do so carefully. Multi-speed hubs are 135mm wide. BMX hubs are 110mm wide. The frame dropouts will need to expand 12.5mm on each side. Move in small increments with rest between to decrease fatigue on metal, but be careful not to overexpand.
Measure distance between dropouts. If 135mm, move to step 8; if less than 135mm, repeat step 6.
Insert new wheel in recently widened dropouts and place chain on drive cog.
Pull back on wheel to set chain tension and tighten the axle nuts by turning counter-clockwise.
Follow manufacturer's directions to install gear shifter. Many different types of hubs and gear shifters are available for this application, but all should come with detailed instructions on gear selection set-up.
Multi-Speed BMX Conversion
Tips and warnings
- It is possible to destroy a BMX frame by widening the dropouts to accept a different hub.
- Doing this conversion will void any and all warranties associated with the bicycle in question.
- Converting to a multi-speed BMX bike is extremely expensive.
- Installing an externally geared rear hub and derailleur system is impossible without major frame welding and parts donated from another bike frame or purchased from a frame builder.