Originally Posted by mtnbke

The idea of putting the faces of the BB shell in a vise gave me chills. Do NOT listen to that advice. You want to spread the chain stays apart, not dynamically bend the entire frame. The entire point of doing it right with a chain stay spreader is you get to choose and isolate where you are putting pressure on the tube set. By clamping at the BB you're risking popping a lug (if its a lugged steel bike) and you have no control over the "where" of the bending forces are applied. With butted tubing you want to introduce the least amount of force necessary to spread the chain stays, not the chains stays AND seat stays if that makes sense. Effectively you really end up doing both, but by focusing "where" the spreading force is applied it can be done right with the least amount of change to the frame. You don't want to over bend then correct. You can get the frame realigned when you do that, but it changes the way the frame rides introducing unbalanced spring rate to the stays.

You absolutely do NOT want to just remove a 4mm spacer from just one side of a hub. Dish is critically important for building strong wheels that "stands." You really want even tension from the drive side to the non-drive side, but with the arbitrary rear dropout spacing we use and with the demands of more cogs the reality is that often the flange on the drive side of the hub is closer to rim/frame center than the non-drive side. Essentially the non-drive side has better "bracing" in terms of the angle. Getting a dish less wheel is important enough that on Santana tandems they use 160mm rear dropout spacing. With 10/11 speeds that creates chainline issues, but you compromise to have a properly balanced tension wheel. Tandems have to carry twice the weight with the same rim and less than twice the spokes, so this matters.

The right way to convert a hub to 126mm is to balance the spacers to keep the wheel dish the same. If you take a 4mm spacer out on the drive side, you need to take a 4mm spacer out on the non-drive side, or you change the dish. The problem becomes if you remove enough spread from spacers that you'll have problems with the chain/cogs and the chain stay interference. Also a 130mm axle can keep the dropouts from properly tightening with the skewer, on a 126mm bike. Check that the axle length of the hub doesn't keep the skewer from properly tightening.

Again, you can fit a 130mm hub into a 126mm bike without doing anything. It just makes getting the wheel in and out a bit trickier, ten more seconds at the most. Better than bending a frame in my book.