How to Measure a BMX Bike Frame

Written by jonathan d. septer
  • Share
  • Tweet
  • Share
  • Pin
  • Email
How to Measure a BMX Bike Frame
The average BMX bike looks something like this. (bmx image by Claudio Calcagno from Fotolia.com)

The frame of a BMX bike has five key measurements: the top tube length, the head tube diameter, the bottom bracket shell diameter, the brake mount post height and the dropout axle slot size. These five measurements will indicate which height of a rider the frame is intended for, which size headset is needed, which style of bottom bracket is needed, which style of brake is needed and which size axle is needed. Both inch and millimetre measurements are standard use in the cycling world and measurement devices used should contain both standards.

Skill level:
Easy

Other People Are Reading

Things you need

  • Measuring tape with inches and millimetres
  • Caliper with inches and millimetres

Show MoreHide

Instructions

  1. 1

    Measure the top tube of the bicycle from the centre of the joint between the top and seat tubes and the centre of the joint between the top and head tubes with the measuring tape in inches to determine the top tube length.

  2. 2

    Measure the inside diameter of the head tube in inches with the caliper to determine the headset size.

    How to Measure a BMX Bike Frame
    A bicycle top tube is the tube the fork passes through at the very front of the frame. (bicycle wheel image by Wendi Evans from Fotolia.com)
  3. 3

    Measure the inside diameter of the bottom bracket shell in millimetres with the caliper to determine the bottom bracket or bracket bearing size.

    How to Measure a BMX Bike Frame
    The bottom bracket shell is the part of the frame housing the pedal crank bearings. (bicycle image by Alexander Zhiltsov from Fotolia.com)
  4. 4

    Measure the distance between the brake mounting post and a perpendicular point on the frame parallel to the centre of the rim braking surface in millimetres with the caliper to determine which style of brake is needed. If no post mounts are on the frame, it will only accept a single bolt side pull-style brake.

    How to Measure a BMX Bike Frame
    Brake mounting posts extend from the seat stay through the centre of the brake arm mounting hole. (bmx détail image by Maud Talêque from Fotolia.com)
  5. 5

    Measure the open axle slot in the frame dropout in millimetres with the caliper to determine the axle size.

    How to Measure a BMX Bike Frame
    The axle slot is the place in the frame dropout the hub axle slides into. (bmx weels image by Alexey Klementiev from Fotolia.com)

Tips and warnings

  • Go to the local bike shop for measuring assistance or examples of size options available.
  • Measurements must be exact. Many parts in the bicycle world differ by only one or two millimetres.

Don't Miss

References

Filter:
  • All types
  • Articles
  • Slideshows
  • Videos
Sort:
  • Most relevant
  • Most popular
  • Most recent

No articles available

No slideshows available

No videos available

By using the eHow.co.uk site, you consent to the use of cookies. For more information, please see our Cookie policy.