05-20-2019, 02:18 AM
While we think of wire-spoke motorcycle and bicycle wheels as similar, the failure causes are very different. The informative book by Jobst Brandt in post 59 applies specifically to bicycles, where most failures are due to weight and fatigue.
Motorcycles can pull more than one G in either deceleration or acceleration. The area of concern to me is the bend in the spoke and how the spoke is not supported in the hub flange. In the picture below, the spokes are supported in the hub in the area below the red line. Spokes work fine in tension, but will fatigue when bent and unsupported.
The traditional spoke wheel has spokes bent at the hub flange, with spokes alternately bending on the inside and outside of the flange. The outside spoke have to be bent more than 90 degrees, the inside ones less than 90. Spoke failure is usually at the bend, and more often, the outside spokes.
In the picture below, you can see that the outside spokes rub against the hub flange, which actually gives them more support and strength. Also, when we think of spokes loosening, it is because the spoke is seating into the hub and the nipple into the rim, not because of spokes stretching or nipples unscrewing.
The black and the yellow arrows point to where the spoke will wear into the sharp edge of the hole causing the spokes to get looser. (It's like valves getting tighter, not because the cam or shim wore, but because the valve face seats into the valve seat)
The ideal is straight spokes, which the Triumph Bonneville went to in 2010 due to rear spoke breakage problems. Their spokes (although stainless) had similar long unsupported areas just like the earlier Honda.
Motorcycles can pull more than one G in either deceleration or acceleration. The area of concern to me is the bend in the spoke and how the spoke is not supported in the hub flange. In the picture below, the spokes are supported in the hub in the area below the red line. Spokes work fine in tension, but will fatigue when bent and unsupported.
The traditional spoke wheel has spokes bent at the hub flange, with spokes alternately bending on the inside and outside of the flange. The outside spoke have to be bent more than 90 degrees, the inside ones less than 90. Spoke failure is usually at the bend, and more often, the outside spokes.
In the picture below, you can see that the outside spokes rub against the hub flange, which actually gives them more support and strength. Also, when we think of spokes loosening, it is because the spoke is seating into the hub and the nipple into the rim, not because of spokes stretching or nipples unscrewing.
The black and the yellow arrows point to where the spoke will wear into the sharp edge of the hole causing the spokes to get looser. (It's like valves getting tighter, not because the cam or shim wore, but because the valve face seats into the valve seat)
The ideal is straight spokes, which the Triumph Bonneville went to in 2010 due to rear spoke breakage problems. Their spokes (although stainless) had similar long unsupported areas just like the earlier Honda.