Not another "cold setting a rear triangle" thread.
 

Yes, another one.

I decided that I'm gonna finally cold set the rear triangle on a bike that I've been jammimg the wheel into for about two years. Why? Just because.

I've read and reread sheldon Brown's method. It just doesn't seem like a good way to do it. I feel his way puts a lot of stress on the top and down tube. I'm considering removing the BB and clamping the shell to my work bench. Then use a hunk of lumber with one end on the bench as far under the seat tube as possible and flexing the seatstay/chainstay/dropout upward. The only downside is maybe not being able to clamp it tight enough.

Any thoughts?

What kind of bike?

The kind of tubeing makes all the difference in the world. If you're working with a carbon steel frame you'll be surprised at how easy it is to cold set the frame. It's been awhile but I've done at least a couple just using my hands.

Follow Sheldon's instructions to the letter and you'll have no problems. Don't ever try to outsmart Sheldon.

Assuming you're not dealing with a carbon frame, you're making it overly complicated. Use the string method Sheldon B. describes to verify the centerline, and a scale to verify original dropout width. Then cold set applying the same principle as for breaking a turkey wishbone, meaning the side held farthest out usually gives first.

Lay the frame on the floor and stand on the lower side of the rear triangle, about one third of the way up. Lift the upper one from the end until you feel it give, and check that you've moved it half the distance needed. Repeat as needed then flip over and repeat for the second side. Double check that the centerline is still as before, then use dropout tools to bring the frame ends back to parallel.

Note, that this method is not 100% reliable depending on how different in strength the chainstays are, which is why you need to keep track of the true centerline. In any case you don't need to get overly concerned over stressing the front triangle because these are always much stronger than one side of the rear triangle alone.

+1000000000000000000000000000000000000000000000

I cold set an old Schwinn Mirada frame using a turnbuckle between the dropouts. Just kept unscrewing until the proper spacing was achieved. Both side are forced apart equally. Sheldon's method looks a bit fraught with peril for the likes of me.

Thing is, only because you're pushing with equal force on both sides, there's no guarantee that they will move equally.

I used a modified Sheldon, laid the bike on a workbench with the rear triangle hanging over the edge, stuck a 2x2 under the dropout, leveraged it against the seat tube and pushed a bit. When it had moved out half the intended spread I flipped the bike over and did the other side. Minimal drama.

Unless you are Jobst Brandt, then feel free to fire away!

Sheldon's method isn't going to hurt anything on a structurally sound steel frame, and it will insure good alignment when you're done. The tools needed are a 2 x 4, a string, and a ruler. Sheldon didn't write instructive articles on these subjects without knowing what the result would almost certainly be. As Grand Bois said, follow the instructions carefully. I also agree with Grand Bois on this point: don't try to outsmart Sheldon. Particularly when dealing with an old steel frame.

If you go with a steel bike from 127 to 130 i wouldnt even cold set the bike... 3 mms is nothing. If you go to a 135 mms rear end i would cold set.

True that is. But it does improve your odds.

This.

His method works; I've personally respaced a frame using his method with no trouble.

Good advice. Me too. I do wonder,why mention his method at all if you think you know better.

+1. And the OP should think about this as well: you've never cold set a frame. How many had Sheldon done, using his method, before he wrote that article? 10? 50? 100? 1000? I think the answer is "plenty." Again, he didn't write this stuff without knowing what to expect the result to be.

Actually, I've cold set two frames using the threaded rod method. They worked fine. But, I want to try something more "controlable". I never said I knew better, that's why I posed the question. My idea is sort of a combination of Brown's and park's: http://www.parktool.com/repair/readhowto.asp?id=43 Remember, there is always a better way to build a mousetrap. Who would have ever second-guessed Toyota engineers?

You said, I've read and reread sheldon Brown's method. It just doesn't seem like a good way to do it.

As has been pointed out, it's a fine way to do it. You are mistaken in your original statement. If you want to use a different method, that's fine, too. At least you are acknowledging the importance of bending one side at a time and taking measurments to insure good alignment.

The method Park describes on their site is the one we successfully used for years in a small framebuilding operation. Keep in mind that you should re-align the dropout faces after spreading the stays to where you want them.

This hits the nail on the head. The only thing wrong with the OP is that it implies that Sheldon Brown's method is somehow lacking, which isn't the case. However, Sheldon Brown never claimed that it's the only method for doing the job, it's just one of many possible ways.

If working with only a frame it's easy to fixture by the bottom bracket, and many frame builders do just that. OTOH there's no need to do it that way as long as you have a method to control and monitor which side of the triangle bends and how far.

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For those who think you can simply insert a jack into the dropouts and assume that equally strong stays will bend equally, here's a heads up.

There's a fundamental difference between how things flex and how they bend. Flexing occurs within the elastic range and is proportional to both the bending moment (force and distance) and strength (inverse proportion) of the parts, so nearly equally strong sides of the rear triangle will flex out about equally when jacked.

But bending (cold setting) occurs only when the elastic limit is exceeded, and since the stays are not exactly equal in strength once the weaker side begins to bend, in accordance with Newton's 3rd Law of Motion, there will never be sufficient force for the stronger side to bend also, so all bending will occur on the weaker member, rather than a proportional response. That's why it's so important to control the process and bend each side separately.

My tip is that when you need to realign the dropouts you can do it with a couple of old axles and four locknuts or track nuts instead of the expensive tools. The real tools are precise and luxurious, but this is appropriately dirt-cheap.

As mentioned at least once above (I only scanned fairly fast) the key is to spread one side at a time. Measure the existing spacing and then spread the one side by 1/2 the amount desired. Then do the other side to bring the spread to the desired spacing. Done that way there's no need to check with strings if you know the frame was straight to begin with. The issue with forcing both dropouts at the same time is there's no way to control which goes and how far. Checking for alignment following such a method would definetly require careful checking.

Sheldon's write up sort of mentions this half the amount on each side but almost casually in passing. It's not stressed strongly enough despite being A key, if not THE key, element for cold setting.