Classtime 

I had my Medici spread by a certificated professional and it is perfect. I wish I hadn’t. It is difficult to put a dollar value on how annoying it is to install a 126mm wheel.

Insidious C. 

Yes that is what I meant. Something to take the place of a bridge (assuming OP bike doesn't have one), limiting the bending moment transfer to the shell. You could rig something up pretty quickly.

gugie 

Bottom bracket shells are made of low tensile steel, and are significantly thicker than chain stay tubing. When building a frame it's common to bend the chain stay sockets to match the angle you need - these are very small bends. If you clamp the chain stays, you'll create a stress riser on the edge of the contact point, and would greatly increase the chance of creasing the tube at the junction point. If the chainstay sockets on the BB bend, so what? When I do 650b conversions I often remove the chain and seat stay bridges, set the width typically to 130mm (which is what most people want) then braze in bridges set at exactly the right distance from the dropouts for a nice fender line without using any spacers. This makes the plastic deformation close to the bottom bracket shell.

I am curious though. If there's no chainstay bridge, which bends first, the stays or the BB shell sockets? Do an FEA analysis on that joint, constrain the faces of the bottom bracket shell, and let me know what area yields first. Make sure you account for the difference in yield strength between the stays and the bottom bracket for accuracy. I'd use 250MPa for the BB. 4130 properties for the chain stays, which is bout 435 MPA. Thickness of the stays could be 0.7-0.8 wall thickness, you can find the geometry at framebuildersupply.com Thickness of the sockets is about 1mm (I just measured one of my raw BB shells since I couldn't find a spec online). I'd do it myself, but I started managing engineers a few years ago and I don't have the SW access anymore. That and the partial lobotomy they give you when transitioning to management wiped out my memory circuits in that area...

dddd

Where the pro methods and tooling is better starts with the tool used, it has a curved face to somewhat prevent the bending force from being as concentrated right next to the bridge or to it's direct attachment at the bb. This not only helps prevent localized creasing, flaking, or visibly-sharp bend adjacent to the bridge, but actually reduces the pulling force at the bridge, instead concentrating the bending load more along the length of the chainstay.

As for the dropout alignment, I discovered decades ago that I could align dropouts to 90% of perfect using only an axle with locknut and cone secured at one end.
The face of the locknut is pressed against an inside face of a dropout and the free end of the axle aims toward (should aim toward, this is just an indicator) the same spot along the opposite dropout's slot. The actual aligning (bending) of the dropout is done on a trial basis using a big adjustable ("Crescent" or "railroad") wrench.

Returning the spacing toward it's previous setpoints usually can be done using far less bending force than your original "spreading) modification, not because the metal has weakened, but because you will be stress-relieving residual stresses from the previous bending (which will help your effort along).
Because of this, when a permanent re-setting is to be done in the best way possible, one should over-bend each chainstay by 1mm, then bend it in to it's final setting.
By doing this, it will take a maximum of force in either direction to go out of alignment, instead of having a very low yield strength in one direction (toward it's previous bend). Yes, this stress-relieving process produces a rear triangle (or fork blade as the case may be after fork alignment) that has the highest, more-equal yield strength in both directions, thus better able to retain alignment under whatever stress/abuse it may encounter in use.

Fivethumbs

I would not worry about spreading the frame either by having a frame builder to it or by doing it myself with 2x4s with a string. I've done it several times with no issue. But you really don't even need to spread it. When Shimano first introduced the 130 mm hub spacing there were no frame builders making 130 mm frames. It was for this reason the first Dura Act 8 speed hubs had convex washers so that when you pulled the wheel into the dropouts the washers would spread the dropouts from 126 to 130. You may be able to find convex washers or just exert a little outward pressure on the dropouts while pulling the wheel in. If you do decide to spread it and change your mind you can always un-spread it later. Columbus Cyclex is fairly easy to manipulate.

Kontact 

If you buy frames to re-sell as collectors items, don't spread the rear. Also don't ride the bike, build it with parts or take it outside of a climate controlled storage facility.

But if you are going to pretend it is a bike and want to be able to insert a 130 wheel easily, spread it. The first thing that ever happened to that frame was someone put it into alignment by bending it.

I've spread maybe 20 frames, without tools. I simply grasped the dropouts close to my chest and pulled them apart. It usually took 2-4 pulls to get out to 130 in steps. Because the frame is symmetrical and the pressure also symmetrical, they always came out symmetrical when I gauged them. Perhaps I was just lucky 20 some times?

If you sell it later on - as a collectible - take those nasty modern parts off and give the stays a squeeze back to 126ish, so the new owner can have the joy wringing his hands about it, and then spread them back out again. Wash, rinse, repeat.


(How do you know it hasn't already been spread to 130 and reset to 126 at least once before? How many owners has it had in the last 37 years?)

gugie 

I was about to write "preach it brother, preach it!"

Then I saw you were spreading them with your own hands, no tools. Wish I had that strength!

Keeping the rear triangle symmetrical by your method can work just fine as long as there isn't a chainring indentation on the drive side, for those keeping score at home.

dddd

I struggle to recall that ever being the case in my experience observing the results of others (and of my own efforts long ago).

As I described in a previous post, the state of residual stress in a chainstay has decided asymmetry after being bent in one direction, so will bend a first one or two millimeters in one direction with almost infinitely greater ease than in the other direction (that it was last bent to). I've literally used just a thumb to correct a deliberately over-corrected chainstay widening on my American Eagle/Nishiki Kokusai, a bike model which wasn't much of a lightweight in 1973!

So pulling dropouts apart with bare hands (or similarly by use of the infamous and time-consuming "threaded rod" method) will usually throw whatever symmetry that the frame had right out the window (by a small or large amount, depending in part on the amount of widening work needed).

As I described earlier in this thread, using tool-free methods (other than, at minimum, a handy measuring rule), one can do this one side at a time, by a measured amount, using primarily FOOT power, even if you're a 140-lb lightweight like me.
And the same method works as well spreading forks (or correcting forks having a steering-pull sort of problem, where usually both legs are found to be offset to one side).

While these are still relatively crude methods (because loading is more concentrated where the tubes meet a fork crown, brake bridge or bb shell when not using tools having a mandrel radius), they seem fine for use on less-valuable bikes (especially those made of less than the highest yield-strength steels).

Thankfully a moderately mis-aligned rear triangle has seemingly no effect on a bike's steering/centering behaviour riding hands-off, but it will force a tilt to the rear caliper, and cause the pads to sit at different heights along the rim. It will also affect the bike's chainline in one way or the other (for better or for worse).

I deliberately spread the rear drops with more outward splay on the drive side of my Centurion Pro-Tour, because it had it's original (as found at the shop's dumpster) "dedicated" 27-inch wheelset on which I wanted to help reduce the dish (this being a bike I would use off-road using single-walled rims, and after having changed from a 5sp to a 6sp freewheel).

Kontact 

Why would the "residual stress" be asymmetric?

dddd

Because it was created while bending to one side is the usual reason, although the final steps of tube processing (including cold-formed "dimpling") can also create asymmetric residual stress distribution.

While a tube is being cold-set by bending, the "grain" of the metal is of course being stretched more on one side and compressed more on the other. The residual stresses thus formed will then allow any net yielding to be more easily set in the opposite direction when a reverse-bending sort of stress is imposed on the tube, at least during the first (what I will call the first millimeter or two) bit of cold-setting in this opposite direction.

There are other ways (mechanical or thermal) of creating or eliminating these asymmetric and other residual stresses, but usually we are simply bending the tube in one direction or in the opposite direction.

At the molecular level, layers or strings of strung-together molecules (mostly having identical spacing) are sliding with respect to each other during cold-setting, usually in a forcefully "indexed" sort of way by one very tiny molecule space distance at a time. Over greater lengths, this can put some of those string/layers in tension, and this is the residual stress. Further displacements past the tube's yield strength tend not to incur an increase in residual stress as just as many strings are being relieved of tension as are being tensioned. A forceful nudge in the other direction allows the strings to again slide along each other in indexed fashion until the residual stress is first eliminated, and then begins to create tensile and compressive residual stresses in the opposite direction. Many such reverse cycles can occur without damaging most steel frame material (some materials much more than others due to alloying, cold-working and heat-treating), though at some point dislocations in the aligned strings of sliding molecules will form and tend to create local misalignments where no sliding can occur (hence, a "work-hardening" of the metal is effected, increasing the yield strength).

Alloying elements added to iron and steel create dislocations along orderly strings of molecules, which tends to lock adjacent strings together at those locations (again, increasing yield strength as molecules then resist sliding smoothly against each other).
Carbon is one such element used to create the dislocations and increase the yield strength, but other alloying elements can serve to distribute the carbon more widely and thus distribute the carbon "nodules" into a greater number of smaller carbon bits, thus further strengthening/hardening the steel.
Cooling steel faster from it's recrystallization temperature is another way of creating more dislocations between and along the orderly strings of molecules, because a larger number of smaller crystals (shorter "strings") then form independently, in differing, unorganized directions, and which reduces the planar size of the "slip planes" where molecular sliding (i.e. yielding) can most easily occur.
Lastly, cold-forging is used to force a "flow" of yielding metal such as to orient the molecular "grain" of the strings of molecules in a favorable direction, AND to crunch linear strings of molecules into more jagged, toothy shapes that resist sliding against each other at all. Such forgings are thus very resistant to further cold-working until much higher working stress levels are achieved.
All of the above is basic sophomore-level materials study from any mechanical/materials engineering curriculum, with steel in particular being a most-studied material.
Frame builders will of course be among those who need to know the mechanics of the materials that they work with.
The rest of us can merely note that yielding steel has a bit of a hysteretic "memory" effect as it is bent in one direction and then the other.

Kontact 

That doesn't really address why the already symmetrically curved stays are going to act differently from each other when equal forces are applied to them.

dddd

It matters not whether the tube is geometrically asymmetric or not, when the tube has been subjected to any side force great enough to exceed the point of yield by what I will say is typically just a millimeter or two of actual yielding. At that point, the residual stresses in the tube is what is asymmetric, whether or not the tube is geometrically symmetrical. A bit of reverse stress-relieving restores the tube's symmetry of bending behavior (requiring same effort in either direction in order to bend).

It's of course invisible what is going on with the strings of molecules sliding around, but the effect of stress-relieving a tube in a direction opposite to how it was last bent is easy to demonstrate immediately after bending a tube. Like I said, I've been able to stress-relieve a chainstay (after bending) to at least a millimeter of "recovery" cold set using just a push with my thumb in the opposite direction, something that would have taken well more than ten times that amount of force in the direction of the first bending.

We usually have no way to know which direction that a tube was last bent, so it may bend quite easily initially or it may require exceeding the yield strength of the tube to get it to bend at all. And that is the main reason why spreading chainstays by pushing them apart will tend to have very unpredictable yielding that is not equal in the two chainstays. Larger amounts of bending going beyond that first couple of millimeters of mere stress-relieving will (based on my observations) also usually show big differences in yield between two chainstays, but for reasons having to do with uneven hardness in the metal, uneven thickness of the metal, uneven heating of the metal during brazing, cross sectional shape variation, etc.

Kontact 

Ah, you're saying that the left might have been bent differently than the right on initial alignment. Maybe - if they were ever different in the first place. There's no particular reason that two tubes handled in the same way and brazed in a jig should be particularly different.

But as someone who has done this probably more than you, in a shop environment with frame gauges available, I disagree that the steel bikes tend to spread asymmetrically. And if they do, it is reasonably easy to fix - so it is hardly an emergency.

dddd

Didn't you say that you pulled the stays apart with your hands?
And can we assume that you measured your countless frames before and after doing so?
Honestly, did you measure anything at all, besides perhaps the inside width of the frames that you pulled apart?

And I have to say, "there you go again", in that obviously we aren't talking about "emergencies" we're talking about making (often small) spacing adjustments to a bike frame. And I don't know about "particularly", are you referencing something "particularly" quantitative perhaps?
You claim to have specialty tools at hand, but do you not use them? Why?
Most frames are going to have driveside chainstay clearance dimples and absolutely won't spread evenly by forcing the dropouts apart, or will they (as one who "has done this probably more than (me)")?. Please also define more exactly what you mean by "this", as you haven't made it clear just what process you had done all those times.

Perhaps one of the frame builders who visit here can clarify any more of your questions.

Kontact 

I would have thought "with frame gauges available" would have made it abundantly clear that I measured the amount and centering of the dropouts I set. But since it wasn't clear to you: I spread the dropouts, checking each side for centering as I did so and then checked the finished product - all with a frame alignment gauge.

And by "particularly", I meant that the majority of steel bikes I have worked on have been very symmetrical - the driveside chainstay was curved and shaped identically to the non-driveside chainstay. No dimples or dents just on one side. All the tubes started out with whatever shape, and then were bent in the same way into the same shape, keeping their symmetry of shape and stress throughout the build process. I can see how bikes with a large chainring clearance dent may bend differently - it would really depend on where the stays tend to bend at all - the tapered chainstays ubiquitous in older steel bikes might have a tendency to bend much closer to the dropout where they are narrower. Dunno - I measured results, not theories.


As a practical matter, my method appears to work pretty well - and has no risks associated with prying against seat tube with a board. Should it fail to move the dropouts the 0.3 degrees necessary in an even matter, then by all means take a 2x4 to it. I'm not saying my method is right and yours is wrong - I'm saying that your theory of how everything works doesn't seem to apply to my real world experience. People can draw whatever conclusion they want about that.

gugie 

@Kontact
"I simply grasped the dropouts close to my chest and pulled them apart"

This is what I was basing my comment on. Lesser strength steel chainstays I can maybe do this on, but I have a grade 4 AC separation on my left wing, so those days are behind me.

gugie 

My "engineering intuition" leads me to believe that stays bend closest to the cross-bracing, which would either be at the bottom bracket or the chain stay bridge (depending if you have a bridge or not). This assumes no indentations whatsoever, which would act as stress risers, and possibly bend there.

I gave @Insidious C. a homework assignment, I'm hoping his corporate overlords don't notice that he's doing mechanical stress/displacement FEA instead of thermal analysis.

Kontact 

They bend where they flex. Is the skinny tubing of the last 5 inches of a stay more or less flexible than at the BB shell where the diameter is double?

gugie 

Think of a straight tube, same diameter and thickness throughout. Clamp it in a vice. Grab the end and bend. It'll bend right where you've clamped it. If you take notice while bending, you'll see that the tubing actually flexes along the entire length, just more so as you get to where it's clamped (constrained for those ME's out there). The moment (Force x distance) is highest nearest the bottom bracket or chainstay bridge. All else being equal, that's where it will bend.

But chainstays taper, and the wall thickness changes from one end to another. The moment calculation doesn't change, it's still highest at the point where the stays are constrained (bridge, unless you don't have one, then bottom bracket shell). But mechanically you have more material there. It may be that an ovalized stay might bend in a different location than, say a 531 rapid taper stay.

But I've learned in my career as an engineer not to believe everything I think. I'm an empiricist when it comes to things like this, but I don't have a good way to measure where the bend occurs (it's only a few mm).

So I bend 'em, wonder where exactly the bend occurs, but it doesn't bother me not knowing. Knowing that framebuilders with tons more experience than I have been doing this for decades without any issues gives me confidence. The rest of this is an academic exercise.

dddd

The point that Gugie made about "stress concentration" is not to be under-estimated.

Not just that the bending leverage peaks just before the bridge attachment point, but that the stress distribution about the circumference of the tube changes radically at this same point, such that the yield stress is first exceeded local to the attachment.
And that also happens to be a place where cold-drawn tubing may have been weakened by torch heat, making this (by my observations, not just theory) the only place along the tube where significant yielding can be observed (other than at any dimple features, for the same reason and because of the weakened cross-section).
The use of special bending tools (having a mandrel radius) can make the bend along more of the length of the chainstay instead of being so localized at the bridge or at any "dimples".

The bending of chainstays or fork legs adjacent to the bottom bracket or fork crown can be complicated not only by the tube's heat-affected zone, but also by any butting of the tube end, or of any internal-lug or external blade reinforcements. One does not usually see any bending of the slender end of the tube even when a bike is involved in a typical head-on collision.

gugie 

I really need to do a video on how I spread rear triangles, as this topic comes up over and over again.

Kontact 

Heat affected zones are hard, not soft with lower yield strength. They are an issue because they can crack because they're brittle.

I dont think you have accurately measured a three tenths of a degree bend in a double tapered tube.

dddd

There you go again, but it totally depends on the alloy. Most cold-worked steel somewhat anneals from brazing heat.

Kontact 

What do you mean? Every decent frame we're talking about is either 4130 or a similar manganese alloy (531). Virtually all of the fancier alloys post date 130 dropouts.

CyclingFool95 

My Montello started life as a 6 speed (126mm nominal). When I went to 8 speed in '94, I found the Chorus hubs (2 different wheel sets) dropped right in. Last year, when I brought it up to 10 speed, I found I needed to slightly spread the frame to drop in the Shamal wheel I wanted to put in it. Didn't exactly take much force, and I didnt bother to set it - if it'll make you happy, tell yourself it makes it that much less likely for the wheel to slip if you dont properly tighten the quick release.