Roger Guillemette ([EMAIL PROTECTED]) writes:
> Greg's point is well taken. The breakage of spokes on new rear wheels
> can be due to poor construction, new spokes loosening up, or weight
> extremes (such as carrying heavily laden panniers with groceries on or
> touring gear). Judging from your description Derek, it may be just
> loosening of new spokes which aren't being attended to. This problem
> increases with wider gear blocks (i.e. 9 or 10 cogs on back versus 6 or
> 7 cogs).
This may or may not be a contributing factor. The problem is the ratio of
the tensions in the non-drive side spokes compared to the drive side spokes,
which is in the opposite proportion to the angle of the spokes from the
vertical (to be really fussy, it's actually WRT to the sine of the angle,
but there's not much difference at the angles we are discussing).
As the gear manufacturers gave us more cogs, the hub manufacturers
increased the width of the hubs - 120 mm for 5 speed, 126 mm 6 speed, 130
mm 7 speed, and I think 135 mm for 8 & 9. These figures are for road wheels
- mountain bike wheels have frequently been one increment wider. This is
one way that the manufacturers have sought to reduce the imbalance in
spoke tensions. In addition, on many recent hubs the non-drive side flange
is considerably further from the dropout than used to be the case with the
traditional 5 speed hub. The critical factor is the ratio of the distances
of the two flanges from the centreline of the hub. So for any given number
of cogs and width of hub, the hub with the non-drive side flange furthest
from the dropout would be the one with the least differential tensions
between the spokes on the two sides.
As always there are other negative effects that follow from this....
SNIP
--
Peter James
Ottawa, Ontario
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