Originally Posted by
Brocephus
Ah,ok, thanks, this is exactly what i was most concerned about. Are 130 and 148mm pretty much the only standards I have to worry about ? ( I just saw that Leebo answered that already. This is getting complicated.)
No the width is only half the information you need for matching the hub axle. There are two "worlds" when it comes to modern hubs -- those with quick release axles and those with through axles. Quick release (QR) is the older and more common style, and probably what you will find on a lower end bike. If the bike you're looking at has disc brakes and is mainly using mountain bike components (e.g. Acera), the rear wheel most likely uses a 135mm QR hub. 130mm is more common on QR hubs intended for rim brake road bikes. Both disc and rim brake QR bikes use 100mm spacing in front.
So the good news is, if your bike uses QR axles, your homework is pretty much done as far as hub standards are concerned. Any QR disc wheelset is likely to have a 135mm over-locknut distance in the back and 100mm OLD in front, and possess a standard Shimano freehub that will work with at least 7-10 speed cassettes (and possibly 11 speed). The rotor mount standard will either be 6-bolt or Centerlock. My impression is that it's a bit easier to find cheap rotors in 6-bolt but maybe that's changing.
If the bike has through axles, it gets more complicated, but most likely it needs a 12x142mm hub on the rear, and 12x100 or 15x100mm on the front. The wider rear hubs (e.g. 148mm Boost, 150, 157) I think are still mostly found on higher end mountain and downhill bikes. I could be vastly out of touch, but I think you're unlikely to encounter any of these standards in a budget wheelset so you probably don't have to worry about them much.
Also, many modern hubs have replaceable endcaps that allow you to convert the wheel between QR and various through axle standards, usually 12x142 at a minimum for the rear and 12x100 or 15x100 in front. These are the only types of hubs I will consider lately since I have a mix of QR and TA bikes now (even my fork mount roof rack has replaceable endcaps!). I don't think Shimano has this feature on most of their hubs so you'll need to know the axle type on the wheels you were looking at.
Here's a pretty good summary of many different hub types (except it doesn't cover Boost...maybe that wasn't available at the time this was written)
https://forums.mtbr.com/wheels-tires...ed-873910.html