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Bearing technics The 8X Series dynamo hubs are suitable for cross country mountain biking, but SP cautions that severe riding conditions be avoided with the 8X series hub dynamos. The 8X series hub dynamos cautions against their use for extreme downhill or severe conditions applications. The QR15 thru axle specification for suspension forks imposes a design constraint requiring compatible hubs to employ thinner bearings than standard hubs. This is due to the fact that the 15mm inner diameter of its hollow axle together with the 6 bolt disc brake specification simultaneously constrain both the inner and outer diameters of bearings that can be used in 8X hubs. This thickness is necessarily smaller than that for standard 9mm hub axles. The resulting thinner bearing races as well as smaller individual ball bearings together that the 8X is, by design, incapable of matching the durability of our 8 Series dynamo hubs.
Additionally, unlike standard QR15 hubs, QR15 hub dynamos require electrical output to be transmitted via wires from the internal dynamo to an external connector. Though physically small, this design requirement nevertheless enlarges the inner bearing diameter and thus requiring bearing thicknesses narrower than standard QR15 hubs. Consequently, bearing thickness for QR15 dynamo hub is smaller than standard QR15 hubs. In theory, 15mm suspensions forks together with the QR15 thru axle should be stronger than standard. However, the mechanical design limitations outlined above mean that the 8X Series dynamo hub will be less durable in practice than the 8 Series hubs. In short, where durability is more important than performance, we recommend 8 Series dynamo hubs.