BILL BOSTON CYCLES

AccuTrax Dimensions
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Dimension Definitions
Setup
Dimension "C"
Dimension "B"
Rake

Many manufacturers do not provide enough information for me to analyze the handling characteristics of your bike. Below are quick and easy methods to calculate those dimensions without special equipment. 

You will be constructing a right triangle, using the extension of the head tube angle as the hypotenuse. The base "B" and the side "C" measurements will allow me to calculate the head tube angle using the formula: HeadTubeAngle = ArcTangent (C/B).

Below is a drawing that defines the dimensions that you will be gathering. You can do the calculations yourself, or just enter the dimensions in the space provided on the request form.

Click on the image below for a larger view, the "UP" button will return you to this page.

You will need the following items:

bike
masking tape
felt tip marker
yardstick
square or plumb-bob
yarn or string
tape measure
a flat level surface

A good place to set up is a deck with a railing but any non carpeted floor is ok. Place your bike with the handle bars against the railing or wall, making sure that the bike is vertical. Use some small blocks or masking tape to keep the wheels and handle bars from moving. 

  1. Set up. Tape the yarn or string (I prefer yarn because it stretches) to the side of your handle bar stem, then run the yarn down the side of the head tube, the fork crown, and down to the floor. Make sure that the yarn is parallel to the head tube and tape the end to the floor. Make sure that the yarn is parallel to the head tube (side view) and place another piece of tape near the top of the head tube to adjust the yarn. 

    Click on image below for a larger view, the "UP" button will return you to this page.


  2. Side "C" of triangle or height of head tube center line at top tube intersection. Place the yardstick against the head tube (behind the cables) and tape it securely to the square. Move the yardstick and square so that the yardstick intersects with the yarn near the top of the head tube. Place a mark on the tape holding the yarn at this point as a reference to make sure the yard stick does not move. 

    The height of this mark is dimension "C" [Definition Drawing], click on the image below for a larger view, the "UP" button will return you to this page.

    Note: This measurement is taken with a yard stick and a square so you don't have to worry about the floor being level. If you use a plumb-bob and a tape measure, take your measurements with the bike facing in both directions in case the floor is not level.


  3. Base "B" of triangle. Place a piece of tape on the floor extending from the edge of the yardstick (the same edge that you aligned with the yarn above) perpendicular to the wall. Measure from the edge of the tape to the place the yarn is taped to the floor. 

    This is dimension "B" [Definition Drawing], click on the image below for a larger view , the "UP" button will return you to this page.


  4. Rake. Measure the rake perpendicular to the head tube angle (yarn). While it may be easier to measure from the center of the wheel if you remove the quick release, taking the measurement above and below the quick release should be fine as long as you stay in the same plane as the head tube angle. 

    This is dimension "R" [Definition Drawing], click on the image below for a larger view , the "UP" button will return you to this page.


  5. Front wheel size.  Measure from the center of the front wheel to the ground.
 

 

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Copyright 2003 BILL BOSTON CYCLES
Last modified: July 09, 2014