Asymmetric rims?

[Jaybee]

Engineers help, please!

Considering having a summer wheelset built for my fat bike - when you have exceptionally wide flange distances on hubs, does it still make sense to use a rim with an offset nipple bed (such as those offered by WTB and RaceFace)? I (nominally) understand their purpose in evening spoke tension on narrower, not really wrapping my mind around how widening the distance between hub flanges would affect that (or not).

[Mark McM]

Offset rims may help with widely spaced flanges, but for a completely different reason than for narrow spaced hubs.

On highly dished wheels (as on most road rear wheels), asymmetric rims can help increase the bracing angle on the drive side, decreasing spoke tension imbalance. Fat bike wheels, which have both flanges spaced widely, typically don't have much problem with tension balance. But they can have a different problem - they can create spoke bracing angles that are too high. If the spoke enters the rim at too extreme an angle, it can result in stress concentrations in the spokes leading to premature failure. To combat this, many fat bike rims have alternating offset spoke holes - the spoke holes for the left spokes are offset to the left, and the spoke holes for the right spokes are offset to the left.

Narrow road rims typically aren't wide enough for the alternating offsets that fat bike rims use, so the spoke holes are typically all in the same plane. This will result in very large bracing angles if a fat bike hub is laced to a road rim - and the non-drive side spokes will have the more extreme bracing angles. To mitigate this, a rim with offset spokes can be used to decrease the bracing angle of the non-drive spokes.

[Jaybee]

Thanks Mark, great info!

I think I follow on the bracing angles being too large for wide hub flanges and centered spoke holes. With that in mind, does it make sense to spec hubs that have narrower flanges? For example, these i9 hubs:



have offset the NDS flange in from the disc mount, especially relative to these DT 350s:



The desired rim will be 40 or 45mm internal width, considerably narrower than the 80-100mm width rims that would be used on really fat tires.