I was considering using the bending technique called cold setting to increase the rear triangle opening on my singlespeed bike from 110mm to 130mm, in order to accommodate a new wheel. Well, I did it. With some trepidation, and hoping not to hear “CRACK!” at any point, and now I’ve got the 130mm I need to accommodate a new SRAM I-3 Motion wheel.
Here are the steps, according to Sheldon “Cold Set” Brown’s web page on the subject:
There are a number of ways to spread a frame. Probably the easiest way is to use a lever. A piece of 2 x 3 or 2 x 4 lumber, roughly 5-6 feet long works well for this:
- 1. Remove the wheels, fenders and any seat-tube mounted bottle cage.
- 2. Lay the bicycle on its side with the handlebars turned to face upward.
- 3. Insert the lumber through the rear triangle, so that it goes underneath the upper rear fork end, and above the seat tube. The lumber should extend out past the rear end of the frame.
- 4. Place the far end of the lumber onto a chair, crate or other raised structure, so that only the head-tube/fork area of the bike is in contact with the floor.
- 5. Press down gently on the lumber where it crosses on top of the seat tube.
- 6. Measure the spacing to see if it has changed.
- 7. If the spacing hasn’t changed, try again, pressing a little bit harder. Repeat until you get a result, applying a bit more force each time, until the spacing has increased by about half the total amount you are seeking.
- 8. Turn the bike over, and repeat for the other side.
I followed his instruction to the T. The first step was to prep my bike – saddle and seatpost off, front wheel off, and rear wheel off. The second step, and one that I learned by searching Google for articles related to cold setting a steel frame, was to bind the rear brake bridge as best I could to support it. I had a cargo cinch strap, so I wrapped it about 15 times around the brake bridge, above and below it, and half-knotted and tightened it down my hand twice. The third step, then, was to cold set the frame. I opened up the right seatstay and chainstay first, going from 110mm to 120mm. I balanced that out by going from 120mm to 130mm on the left side, which I did by flipping the bike over and proceeding as above.
And voila! The wheel fits fine. The only thing is, I’ll have to buy a new chain – the new rear sprocket and wheel insertion spacing put me 2 chain links short of the right fit.
I cold set my steel framed singlespeed tonight. I’m a regular bike hack now!