The dimensions of the fork.

The dimensions of the fork.

maatvoering van de vorkFor the proper selection of the front fork, the following sizes are important. See image (28)

  1. The thread size. The most commonly used thread is BSC 1 “x 24 TPI. In addition, also used with metric thread size of M25 x 1, Italian thread 25,4 mm x 24 TPI, and oversized screw BSC 1 1/8 “x 26 TPI and BSC 1 1/4” x 26 TPI.
  2. The length of the screw thread. The thread length must be sufficiently long so that the stem head can still be held
  3. The length of the inner head tube. This should be sufficient to screw the top stem nut still on the fork, See Figure (29)
  4. maatvoering van de vorkThe press fitting to the fork cone. For steel fork crown pieces and cones, the diameter should be 0.2 mm smaller than the inside diameter of the crown cone. With aluminum crown pieces or house of the cone, the diameter should be 0.1 mm smaller than the diameter of the crown cone.
  5. The width of the fork in the crown piece. This is the maximum bandwidth that can be used.
  6. The distance between the center point of the fork dropouts and the bottom of the fork crown. This is the maximum wheel radius (possibly including the mudguard) that can be used.
  7. The inner diameter of the fork dropouts. This is the installation dimension for the hub.
  8. The jump. This is the deflection of the fork.

Before a fork is fitted, or if the fork is bent, the dimensions should be checked and repaired if necessary.

In addition, the application for the fork cone is to be milled and the fork are made to length, so that the ball head bolts can be properly fitted.

maatvoering van de vorkChecking the measurements is done with a special control and pointing device and is as follows ( see figure 30 ):

  • Put the steerer so that it can rotate only.
  • Put plate A against the crown piece so that the crown piece is parallel to plate A, and now put the fork securely.
  • Now check with pin B or fork sheaths parallel to each other. Pin B must come against both fork sheaths.
  • Check with pin B if the dropouts are equally distant from the axis of the fork. The pin can be placed in the dropouts of the fork.

If the fork appear to be bent, it can be gently bent back. For this purpose a special fork bender is available with which a considerable force may be exerted on the fork.maatvoering van de vorkSee Figure 31.Only small deviations from the fork sheath can be corrected safely. With large deformation the material is damaged too much, and needs to be replaced the fork. Forks of aluminum alloys should not be bent back. The risk of brittle fracture of the aluminum is then too large.

The dropouts can be put straight with a dropouts straightener just as the dropouts of the swingarm. It should also be taken into account the installation width of the hub.


To compress the fork cone right on the fork, they should have a good straight fit. A special fork cone cutter is available. There are cutters available for headsets 1 “, 1 1/4” and 1 1/8 “, maatvoering van de vork See Figure 32 .
Using the right milling head ensures proper fit.
It should also be taken into account with the material of the cone.
If an aluminum cone is mounted. Then it must outer diameter of the crown piece 0.1 mm greater than the inner diameter of the cone. With a steel cone is the difference 0.2 mm.

To install the fork steerer it should be sawed to the correct length. The correct length can be determined in three ways. The simplest is to take the old fork as a measure to substitute.

Also, the length of the head pipe can be measured.
After this, measure the height of the bearings must be added.
The resulting length is the length of the steerer tube from the crown piece. The fork can also be fitted without locking nut. Above the locknut must remain 5 mm screw for fixing the locknut. After the appropriate length is determined, the head tube can be cut to size. To ensure that the tubing is cut straight, there are special cutting molds available. After the cutting process has to be re-cut the thread in order to be able to rotate the stem head smoothly on the tube. maatvoering van de vork See Figure 33.

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