I'll guarantee you that when you flex the stays apart by hand, each side is not moving the same amount off of center. In fact, you're probably moving one side 4mm and the other side none. So with the wheel in the frame, you've just misaligned the rear triangle by 4mm. Or maybe 3mm. Or maybe 2.5mm. Who knows.

The advantage to cold setting from 126 to 130 is that, if done right, you can have a frame that's properly aligned at the wider spacing. With some frames you can even end up with better alignment than you started with.

And any good bike shop can make sure the dropouts are aligned properly, and correct it if not, and can check derailleur hanger alignment and correct that, too.

If it's worth doing, it's worth doing right. And I'll add that if someone is changing the frame spacing to run a modern 10 speed cassette with indexed shifting, for example, the derailleur hanger alignment is critical.

I would cold set the frame. While the good colonel is right that it's only 2mm per side, I also agree with well biked that you cannot guarantee that the stays will be aligned properly. From what I've read, you really wouldn't have to align the dropouts for a 4mm set as it doesn't change the angle enough to matter. If you're spreading 10mm like I did, then aligning the drop outs becomes more necessary. Supposedly broken axles can occur.

That's conjecture. You guarantee something in the beginning of the paragraph, but by the end you don't know.

Likely. I wouldn't know or care as I use friction shifting exclusively.

I'm not advocating that the OP not have his frame spread. It's his bike to do with what he feels best. The new Shimano 105 hub that I just put in my '87 Voyageur with 126mm spaced dropouts went in easier than the front wheel. It has been my experience that cold setting the frame for 4mm difference isn't necessary. That is all.

My experience can confirm this as well. I've never had a rear derailleur issue after forcing in a 130mm hub, but I've also not used 10-speed. I'd only bother to cold-set if spreading more than 4mm or if it was difficult to get the 130mm hub in. It hasn't been yet.

I'd like someone to show me a frame that has worse alignment with a 130mm hub forced in than when it's running a 126mm one. Not 'cause I don't believe that it happens, but that I'm curious, and that I really have my doubts that most frames are that accurately aligned in the first place. Particularly ones that have seen a bunch of use, like many C&V bikes.

Nope, you misread. I guaranteed you could not move each side of the rear triangle the same amount off of center by flexing it apart by hand. And I stand by that. I wouldn't have responded at all if you had not used the term "it's 2mm on each side" in an earlier post. That misconception bugs me, it simply does not happen. By flexing the frame apart by hand and stuffing a wider hub into the frame, you change the alignment of the frame, at least a little, in every case.

Experience tells me it's most often 4mm (or however much you widen the spacing) on one side, zero on the other. It can vary. But it will not be equal amounts on each side, I guarantee you.

What I wonder is: how does that compare to the alignment that was there before the stuffing was done?

I have strong doubts that many frames out there are very well aligned, and we don't seem to mind. For example, many of the older frames I've had have more than their original 126mm spacing - the back end seems to spread out from use over time. I really doubt that this happens evenly.

I'm not questioning you well biked, just curious. Have you measured alignment before and after spreading? Was the frame in alignment before spreading, and if it wasn't, did the rider notice?

Physics and experience tell me differently. If the stays are made out of the same gauge material and are the same shape and profile please explain how one would move 4mm and the other wouldn't move at all.

(meant to quote well biked)

To the OP: I'm with bigbossman here. If you are committed to a modern 130mm drivetrain, have the rear end spread. That bike is good enough for the "no compromises" treatment.

I have had good frames spread from 120mm (531 frame) and 126mm (SLX and unknown but high-end mix) to 130mm. In all cases, I let the pros from Dover do it. At the same time, I had the overall alignment checked and, if needed, corrected. It has never cost more than $50 for the whole enchilada. It would be more if there was a signficant alignment issue, but not more than another $20 or so.

For a top-drawer C&V steel beauty, this strikes me as dirt cheap insurance that the job is done right and that everything is in proper alignment.

I'm not sure they are the same shape. Drive-side chainstays usually have a considerable dimple to clear the chainring, in addition to the dimples both chainstays usually have to clear the tire. I'd expect the difference in bend (if any) to be concentrated where the chainring dimple is. Certainly at that location the drive-side member is less resistant to sideways bending moment than is the non-drive side member.

And what makes sure the owner's applied forces are symmetrical?

I've had several frames gone over by a good aligner. In all cases the riding improved significantly. I'd let the frame work be done by an experienced person who understands it and is equipped.

Umm...If you're not cold-setting, it's gonna take the exact spread of the wheel/hub/axle you're putting in there. If the dish of the wheel is correct then the spread is gonna match that. The dropouts are resting on the axle nuts (or axle washers if you need clearance like I just did on the Batavus Pro) and will be equidistant from center of the axle as it springs into place. You are describing cold setting something unevenly.

Well said. To me, if the 130mm hub goes in, then you're good. That's also been my first hand experience.

You're right. I'll slink off now. My apologies to ColonelJLloyd.

None necessary. That's just what we do here, right? Discuss bicycle minutia ad nauseum or until we can go home and ride bikes.

^^^ Exactly...no harm...no foul.

Yeah 2mm in my experience, too.

Maybe, maybe not. It all depends what components he's going to run. Misaligned dropouts immdiately put the axle into bending stress. Indexed shifting does not tolerate hanger misalgnment well when using high cog counts and improperly postioned axles in older, horizontal dropouts. Sometimes you can get away with it and sometimes you can't.

I'm actually having a problem getting an 11-26 with indexed shifting (DA short cage RD, DA shifters) to run properly in the highest 2 cogs. I'll probably take this to an LBS to get this confirmed, but this sounds like it could be an issue.

Things should work the way they're supposed to. If you have to pry the dropouts apart to get the wheel in, it's a situation that needs to be corrected.

For indexing especially, aligned drops are the first step, then, alignment of the derailleur hanger, that is vital in my view for happy shifting throughout.
It is possible to get by with just aligning the hanger, but why load the axle askew?
1 to 2 mm is probably tolerable.

I have the original Shimano hanger alignment tool set, which I always found funny suggested using a Campagnolo hub to be used in conjunction with it...not in the tech handouts, but in conversation with them when SIS first came out, they said a loose Campagnolo hub they knew would probably be at the disposal of most pro level shops...

I'll be the voice of dissent here...

First off, I have no problem with cold setting frames and have read enough to know it's not a huge deal (and is even reversible). Personally, I'd rather get a 130mm frame if I want a modern drivetrain and I'd leave the classic as is. I do think repsacing to 130mm negatively impacts value (I say this based on experience both buying and selling) and given how many 130 spaced frames are out there, I just don't see the need.

I think I'd cold set it back to original spec if I was worried about cold setting impacting the value. It is reversible after all.