Forces in the spokes.
Spokes can only absorb tensile load. When pressure is applied they become loose. Because they are hinged in a wheel, they can not bend. If the wheel is loaded, the hub moves a little bit down. The spokes above are then stretched in the wheel, the spokes at the bottom of the wheel, a bit to be relaxed.
In order to ensure that the spokes which relax are not to become loose, they must be adjusted to preload.
With the pre-tension spokes are permanently stretched. The greater the tension for the less likely it will prevent a spoke becomes loose. In general, a wheel should feel tight. The prestressing is more likely to be too low or too high.
The prestressing is difficult to measure. You can do this a little determine by feel, listening (the higher the spoke sounds the tighter the wire) or to be measured.
To measure the tensile force of spokes there is special wire strain gauges available. The pulling force in the spoke must lie with use of aluminum wheels in the front wheel between 550 and 800 N.
The rear wheel the pulling force may be slightly higher. When using steel wheels the pulling force should be between 600 and 1000 N.
Because in the wheel, spokes per pair at an angle to attach to the hub, the wheel will also get in the lateral or axial direction strength and stiffness.
The greater the angle of the spokes, the stronger and stiffer the wheel is in the lateral direction. The spokes on the front wheel, making a larger angle than the spokes on the rear wheel. The front wheel is in a lateral direction, therefore stiffer.
The spokes on the rear wheel to make a smaller angle, because the distance between the hub flanges can not be made wider.
In bicycles with a derailleur gear is at the rear wheel on the right side of space required for the mounting of the chain wheels. In order to center the wheel still good the rear wheel must be strong umbrella-spoked. The spokes on the drive side walk much steeper towards the hub.
The spokes have to have the same tension at a symmetrical wheel, in order to prevent a stroke come in the wheel. If a spoke on the left pulls harder on the rim then on the right, the spoke will draw a sidestroke in the rim to the left. If a pair of spokes in one place tougher draw in the rim in a different place, there will be a high stroke coming into the rim. In an umbrella-spoked wheel for the tension on the side of the freewheel is larger in order to create balance in the lateral direction.
The most simple spoke pattern is created by connecting the hub in the shortest possible line with the rim. This radial spoke pattern provides a strong and rigid wheel in axial and radial direction. A radial spoked wheel can not be recorded moments on the hub. If a moment is exerted on the hub, the hub must be balanced by the spokes.
This is only possible if the lines of action of the spoke forces do not pass through the center of the wheel. In order to ensure that they can exert a reaction moment they are being put on the hub at an angle. In order to achieve this, the wheel can be woven in different patterns. The strongest wheel is created by placing the spokes at an angle of 90 ° on the hub.
The spoke pattern thus created is indicated with the number of spokes that crosses the spoke.
In the wheels 622 is generally about 1 over 4 spoked. Each spoke crosses than over 4 other spokes.
Also used are 1 over 3 and 1 over 2-spoke patterns.
In the wheels with a high flange and wheels 559, about 1 over 3 is used because the distance between the hub and the rim is too short to spokes 1 over 4.
By driving and braking forces of hub brakes there is provided a moment force applied to the hub.
In these wheels, the spokes are to be placed at an angle.
For the strength the heavy duty spokes have to walk on the outside of the hub.