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Sizing For Bikes, Parts and Accessories

1.  Frame Sizing
- Road Frames -
To determine your correct frame size, you will need your actual inseam length. This is a measurement for bike sizing purposes and will likely be different than your pants length. For this measurement, stand in stocking feet with your back against a wall. With your feet about eight inches apart (pedal width), place a carpenter's square (a notebook also works) tight against your crotch. It should be tight enough to simulate sitting on a bike. The other plane of the square should be against the wall. With a yardstick, measure from the floor to the top of carpenter's square or notebook. Repeat several times and average the results. If you measured in inches, convert to centimeters by multiplying by 2.54. To find your frame size, multiply your average inseam in centimeters by .67. For example if your inseam is 33 inches, multiply 33" x 2.54= 84cm x .67= 56.28 cm. The frame size for a 33 inch inseam would be 56 centimeters.

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2.  Bottom Bracket Sizing
There are 2 components to Bottom Bracket (BB) size, the BB shell width of the frame and the spindle length.

Bottom Bracket shell width:
The BB shell is the frame tube into which the BB threads. It will measure 68mm, 70mm or 73mm wide. Measuring the shell is easy. Flip the bike upside down and use a metric ruler or calipers to measure across the shell on a line parallel to the BB spindle. Do not measure any of the old BB if it protrudes beyond the shell. This measurement will also determine which threading your frame is likely to have. 68mm & 73mm shells have English threading while 70mm is Italian.

Below are pictures of how to measure shell width. The first picture shows the measurement being taken without the BB installed (left), the second is with the BB installed (right):
Spindle length:
To find the length of the spindle, first remove the crank arms. Then measure the length of the spindle in millimeters from end to end. If your cranks are attached with nuts as opposed to bolts, do not measure the extended threaded portions of the spindle.

If you are replacing a BB and are using your old crank, you'll want a replacement BB with the same spindle length. If you are installing a new crank, you will want to use the spindle length recommended by the crank manufacturer.

Below are pictures of how to measure spindle length. The first picture shows the measurement being taken when the BB is out of the frame (left), the second is with the BB installed (right):

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3.  Crank Arm Length Sizing
Crank arm length is measured in millimeters from the center of the crank bolt to the center of the pedal spindle (where the pedal attaches to the crank arm). The most common sizes for crank arms are 165mm, 170mm, 172.5mm, 175mm and 180mm.
Crank arm length is generally a function of two characteristics: leg length and riding style. As a point of reference we have provided below recommended crank arm lengths based on frame size and inseam length. These measurements may be adjusted based on riding style, but the majority of riders will find that the recommended lengths will provide optimum performance.

Experienced cyclists may select crank length based on their riding style. Riders who feel more comfortable turning big gears at lower cadences appreciate the greater leverage afforded by longer crank arms while riders who prefer to stay on top of their gears and spin at a higher cadence benefit from the use of shorter crank arms.

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4.  Handlebar Sizing (Road)
Road handlebars are produced in various widths. The width of a handlebar is measured in centimeters across the drops (this is the bottom of the curved portion of the bars, pointing toward the rider). Most companies measure their bars center to center but others, TTT's bars for example, measure outside to outside.

As a general rule, the size of your handlebars should be equal to the width of your shoulders at a line through the shoulder from the armpit. Some riders prefer wider handlebars for easier breathing while other riders prefer narrower handlebars for greater aerodynamics and maneuverability. A properly sized bar should strike a balance between comfort, aerodynamics and your particular riding style.

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5.  Stem Sizing
There are two types of stems: threaded (quill) and threadless.
Threaded stems have a quill that slides into the fork steerer and is tightened by a bolt and wedge. Threadless stems, on the other hand, clamp directly to the steerer tube and are tightened by one or more bolts that bind the stem to the fork.

Stems are defined by their Intended use, Length, Diameter and Rise.
Intended use: Stems are made for either road or mountain bikes and they should not be switched. They differ in their handlebar clamp diameters. Road handlebars have larger clamp diameters, typically 25.9/26.0mm while ATB bars are narrower at 25.4mm.
Length is measured along the stem from the center of the quill or steerer tube to the center of the handlebar clamp. It is given in either millimeters or centimeters, typical length are 90mm/9cm, 110mm/11cm or 130mm/13cm.

Stem diameter is really a measurement in inches of the fork it is to be used with. More accurately it is the measurement of the outside diameter of the fork's steerer. Common sizes are 1", 1 1/8" and 1 ¼". Many threadless road stems come with shims so that they can be used w either 1" or 1 1/8" forks

    Threadless
    • 1"diameter steerer = 1" diameter stem
    • 1 1/8" diameter steerer = 1 1/8" diameter stem
    • 1 ¼" diameter steerer = 1 ¼" diameter stem
    Threaded
    • 1" diameter steerer = 7/8" actual stem diameter (order 1")
    • 1 1/8" diameter steerer = 1" actual stem diameter (order 1 1/8")
    • 1 ¼" diameter stem = 1 1/8" actual stem diameter (order 1 ¼")

    Stem Rise is a measure of the stem's angle relative to the headtube or fork angle.

    • A stem perpendicular (90º) to the headtube/fork angle has a 0º rise
    • A stem which angles above perpendicular has a positive (+) rise
    • A stem which angles below perpendicular has a negative (-) rise

    For most road bikes a stem parallel to ground will be -17º.

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6.  Headset Sizing
There are two types of headsets: threaded and threadless.
Any bike frame will accept either type of headset as long as it is the right size for the frame and the right type and size for the fork to be used. Threaded headsets will only work with threaded forks and threadless headsets will only work with threadless forks. A frame designed for a 1" headset can only be used on forks with 1" steerer tubes. The same is true for frames designed for 1 1/8" or 1 ¼" headsets.

Headset size is determined by the outside diameter of the steerer tube on the fork. The most common sizes are: 1" and 1-1/8". If you only have the frame and no fork, you can determine the correct size headset and fork you'll need by measuring the inside diameter of the frame's headtube:

  • 30.2mm headtube inside diameter = 1" headset and fork.
  • 34.0mm headtube inside diameter = 1 1/8" headset and fork

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