You are reading a single comment by @AlexB and its replies.
Click here to read the full conversation.
London Fixed Gear and Single-Speed is a community of predominantly fixed gear and single-speed cyclists in and around London, UK.
This site is supported almost exclusively by donations. Please consider donating a small amount regularly.
@AlexB
Dropout spacing, axle lengths and hub/cog spacing are not the same things!
Think about it like this: imagine a line running along the centre of your bike from the BB to the centre of the rear hub.
When people talk about a 42 or 46mm chainline what they really mean is that from this centreline to the cog is 42 or 46mm.
The axle spacing is the width of the rear hub plus all the spacers and should more or less match your frame. You can fit a 135mm hub into a 130mm steel frame and a 120mm hub will fit a 126 steel frame, but a 135mm hub into a 120mm spaced frame is a stretch too far, as is a 120mm hub into a 135mm (MTB) frame! You are safe enough with steel frames, but alloy frames might develop a crack if stressed like this.
Most hubs have one chainline regardless of the axle spacing offered. So for example a 42mm chainline hub might be available with 120, 130 and 135mm axle spacing. It will be the same forged hub body and the cog will sit in the same place. The difference is the thickness of the spacers added to the axle on each side of the hub body. so a 120mm hub might have 10mm of spacers either side and a 130mm hub would have 15mm.
Axles tend to be sized to match the longest spacing on cheap hubs, so a 120mm hub might have the same axle as the 135mm hub, the difference being that on the 120mm hub you end up with a bit more bare axle sticking out of the tracknuts when they are tightened down.
The exceptions would be quality hubs where the axle will match the hub spacing and Phil and Goldtec type hubs which use allen key fastenings and the axles are sized for the hub spacing, since the axles do not stick out beyond the frame, the bolts screw into the axles instead.
So for your first question:
130mm spacing on the frame. If you buy the 135mm hub, you'll need, ideally to remove a spacer from either side of the hub to reduce the hubs width. OR you can fit it as it is and it will spring the frame out 2.5mm either side. This should be fine. It will not affect the chainline at all.
The chainline is tricky. Ask in the shop, they should know roughly where that cog lines up to on an MTB triple. My guess is that it will line up with the middle chainring.