You are reading a single comment by @Diamond_Supercool 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.
@Diamond_Supercool
Turns out I couldn't find a threaded bar long enough for my purposes and reading threads like this one convinced me that my frame really could be attacked with a piece of 2x4 and live to tell the tale.
Given that there's not a vast amount of detailed guidance around, consider the following my service to the internet. Though frankly there's not much guidance needed.
TLDR: I increased the spacing of my dropouts from 120mm to 127mm with no dramas. If you're not an idiot, Read Sheldon and get on with it. But be careful.
Pictures
1) The bending bit. Note the need to have someone standing on the headtube
2) The alignment/symmetry measuring bit
Method
I worked pretty slowly, gingerly and methodically. It took about an hour to take the frame from 120mm to 127mm (which is as much as I needed to fit my wheel in). I would have been happy taking this frame all the way to 130mm.
1) Pick a side to bend. Thread your 2x4 (mine was about 4.5ft long) according to Sheldon's method. I used a chair at the other end
2) Do some bending. You'll probably need to gradually add most of your bodyweight.
3) Measure total distance between dropouts. Make a note of it.
4) Wrap string round frame, according to Sheldon's method, then measure distance between string and centre of seat-tube on each side. Hope that one side is noticeably further out than the other (perhaps 1mm). Make a note of measurement on both sides.
5) Repeat for other side of frame, hoping that the total spacing between dropouts increases by about a millimetre and that the spacing between the string and the seattube is now the same on both sides. NB: The distance between string and seat-tube will vary each time you attach the string. That doesn't matter. What matters is that it is the same on each side.
6) Repeat process until you've got the desired spacing between dropouts and an equal spacing between string and seat-tube on both sides. Key stage 1 maths will help.
Recommendations
1) Allow plenty of time. It's easy but it takes a while to do properly.
2) The right side may bend more easily than the left due to the cutout on the chainstay put there to accommodate the chainring.
3) The bending is easy at first, then becomes more difficult
4) For added effect, increase the height of the chair. (Putting a toolbox on top of the chair massively increased the rate at which I could bend the frame)
5) Beware of snapping off cable-guides, chain hangers etc.
6) Be careful, but don't worry too much about bending the seattube. I didn't seem to make even the slightest dent in mine.
7) You needn't totally disassemble the bike. The headset, seatpost, BB, cranks and forks could probably all remain attached.
8) If you have a big enough clamp, I'd probably recommend clamping the seatstays together either side of the brake bridge, though I didn't.
9) Quality of steel probably makes quite a big difference. This was Reyolds 531c.
ps: Dear Google, here are some keywords for this post: bicycle cold setting dropouts 120mm 126mm 130mm steel frame spreading alignment string method Sheldon Brown how to