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Been wanting to build a new set of wheels for my trail rig. Since my bike uses rim brakes, which work good enough to not upgrade to disc's, I'm going to re-use my old rims. Problem is they are 48 spoke. There isn't many options for 48 spoke hubs in the mountain bike search results, But many in the bmx search. Wondering if anyone has done this or just has the knowledge of why or why not this would or wouldn't work..thanks a lot.

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You could do this by respacing a standard axle (as opposed to proprietary) 3/8" BMX hub. The freewheel thread is the same as long as the BMX hub doesn't take only metric or LHD freewheels. It's something a tinkerer might do for fun to make use of some rims. There are some issues that may hold it back from practicality:

  • Current standard 3/8" axle 48h BMX hubs are more or less garbage parts. Almost by definition they only have 48h for looks at that point, since real freestyle bikes use 14mm rear and race bikes never use 48h. There are probably pre-14mm hubs that are counterexamples, but I can't think of any that use standard axles.
  • The extra strength and durability of it being a 48h wheel would be somewhat wasted given its vulnerability to bent axles, being a freewheel hub.

Some BMX rear hubs have flange to flange distances that are significantly greater than the 57-58mm numbers usually found on 135mm MTB hubs. You'd want to avoid that, because making a derailer wheel out of one would give less lateral strength.

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You've got problems before even getting the freewheel on the hub; a bmx bike normally uses 110 mm rear spacing, whereas a mountain bike typically uses 135 mm rear spacing, so you wouldn't be able to mount the wheel in the frame to start.

Rims with brake tracks aren't that expensive, though buying a full wheel is likely a cheaper option than building one up yourself.

If you really want to build up a wheel for your mountain bike using a 48 hole hub, Phil Wood will make one that takes a freewheel.

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