I've been shopping around for replacement wheels for my 10 year old Specialized Tricross, which came with an AlexRims Ace 19 rear wheel with a 130mm O.L.D. hub. I measured the rear dropout at 131.3mm with a set of digital calipers.
Now I'm getting confused about hub width. Sheldon Brown's article on hub width lists 130mm for road 8-10 speed wheels (my bike came with a 9 speed cassette), and 135mm for MTB 7-9 speed.
However, I'm seeing a lot of wheels that I think are meant to be road wheels but which come with 135mm hubs. I understand there's some bleed over between standard road and MTB hub widths for particular disciplines like Cyclocross and touring and such, but I'm confused about why I'm seeing a lot of wheels I'd consider firmly in the road discipline, but built up with 135mm hubs.
Here are a few examples:
The latter is notable because it's specifically a narrow road rim aimed at "Road Racing" according to AlexRims.
Is there some industry trend that explains why so many wheels seemingly intended for road bikes are using MTB hubs/ hub spacing?
Is it just a fluke that I've stumbled on a bunch like this? Are these wheels, admittedly at the cheaper end of the spectrum, actually aimed at hybrids, not road bikes? (follow up: do hybrids use 135mm generally?)
Or, as discussed here, does this have something to do with a proliferation of disc brakes on road bikes? If so, why does that affect these rim-brake wheels? Have frame builders moved towards a generic frame spacing that can then be finished with either disc or rim brake mounts based on trim level?