Drillium Dude 

...but how do you measure the width of your rear triangle at the DOs?

I'm messing about with a bike this morning and figured I could swap wheels (both with six-speed FWs) directly across from one bike to another for a test fitting of the drivetrain. Came upon a snag: the spacing is not the same.

The Davidson frame I am taking the wheel out of measures 126mm, measured between the inside DO faces. It's 120mm on the Medici (the bike I'm trying to put together). The wheelset that was in the Medici fit fine, and has a six-speed FW, so I'm wondering what's going on here. I won't be re-using that set as it will be going up for sale.

I mean, I know the rear ends represent two different widths, but how's a six fitting in a 120mm rear end? Isn't the max supposed to be 5 for a 120?

It appears I may be able to find a bit shorter axle/spacers to get the spacing on the hub correct, but then will I be able to fit a six-speed? Frame is from 1979.

Thanks in advance for any assistance

DD

iab

Doesn't a narrow 6 fit in a 120?

But this is a bit outside my wheelhouse.

iab

As usual, Sheldon explains it the best.

https://www.sheldonbrown.com/freewheels.html#speeds

Drillium Dude 

Mine, too. But it just so happens this is a Shimano FW - the only one I own, as a matter of fact. Maybe it's a Narrow Six.

I think I'm going to have the rear end spread. 126 would've been standard by 1979 I'm thinking - right?

DD

iab

Measure the freewheel. From center of the #1 cog to the center 0f the #6 cog would be 25mm on the narrow and 27.5mm on the "normal".

CrankyFranky

Are the hubs identical? Do they both have stock spacers/locknuts/knurled nuts on ‘em?

Assume that the freewheels are the same? I'm all for measuring both.

Are the small cogs the same tooth ##?

This might be too much more than you’d want to do, but (say) if you removed both freewheels and measured the distances between the hub freewheel shoulder and the knurled nut (DO face), are the two measurements identical?

If you have a dishing tool, are the FW-side measurements the same for both wheels?

Are the seat stays on the Medici slimmer than on the Davidson at the DO end?

This is a great question!

In early 1980s, one could find both 120 and 126. My ‘ 82 Stan Pike was 120, perhaps because he was a small custom builder at the end of his carreer, too busy to keep up with emerging trends, and I was too busy at Uni to be aware of six speeds either, never mind that I ordered it in mid 1981.

CliffordK

I'm not sure I have any 120mm frames. I think mine was 126mm for 5x2 gearing.

Anyway, I always remember quite a bit of space to the right of the freewheels, but perhaps that was also required for larger sprockets. So, it is possible that a narrow 6 speed freewheel would be close to fitting, especially if you go with 12T, or maybe 13T.

You may choose to cold-set your frame to 126mm, and be done with it.

Otherwise, I'd set your spacers with minimum spacing on the right, then adjust your left spacers, and see how it comes out.



I suppose you won't see the final dishing on the wheel until you're actually finished. Double check your derailleur hanger is straight.

You can also source a 5s freewheel, mount, and adjust the spacers and cut the axle.

RiddleOfSteel

Given my experience, 1979 was in the middle of a transition period for rear spacing. Some mid-late '70s bikes had them (high-end only) and by the early '80s a number of mid-level and up bikes would have switched, but maybe not as many as any of us would think. I think Treks were 126 pretty quickly (if not immediately?), and Schwinn was a little slower ('84 Super Sport, below Peleton and Paramount, was 120mm), but by 1985 was pretty with it in the upper half of their range. I probably wouldn't worry about spacing a 120mm to a 126mm, especially as you are running friction. It's steel, so it's going to be pretty happy with a lot of things.

rccardr 

You do know that the hub shell for a Campagnolo 120 is the same as a 126, right?
Could be just a matter of removing the 5mm spacer or a couple of the washers and redishing.

Ghrumpy

This is good advice. Measurements matter more than "standards." And the 120 and 126 "standards" are pretty loose, as we've recently discussed elsewhere.

So the first thing I'd do is measure the actual hub OLN widths. There's a chance your hub that's been in the 120mm frame is a bit more than 120.

"Ideally" the hub spacing should follow the freewheel width and desired chainline, but that's a lot of measuring and math, so the tendency is for 5s wheels to be 120 and 6s wheels to be 126 for convenience sake. There's no reason you can't run a 5s freewheel on a 126 hub but a 6s standard FW on a 120 rear hub is pushing it; your wheel will have quite a lot of dish and axle overhang and the problems that often result from those conditions. A 6s Ultra freewheel will be a little wider than most 5s standard FWs but usually fits a 5s hub without major axle respacing if any.

If you really want to swap wheels from one frame to another with their different rear triangle widths, you could just split the difference on the rear hub spacing and set them both at 123mm OLN, which should be just ok with the 6s freewheels and won't cause long-term problems for your frames. I've seen this sort of "compromise" spacing on frames too during that 5 to 6 transition period. But if the freewheels are different widths you'll have to readjust the limit screws when switching from one freewheel to another. And you might end up having to swap an axle or two to get the length right. Might be more trouble than it's worth in the end.

gugie 

To the OP's original question,

"how do you measure the width of your rear triangle at the DOs?"

Answer: to be really accurate, with a set of calipers. +/- millimeter with a tape measurer. +/- 0.5mm, a ruler.

+/- 1 mm is really all you need. When I respace rear dropouts, it's kinda difficult to get them with an error of less than 0.5mm. In usage, this is close enough.

pastorbobnlnh 

Shimano never produced an Ultra or Narrow spaced six speed freewheel. So this rules out my first guess about your challenge.

Drillium Dude 

Well, yeah - that is the basic gist of my problem: the distance between the two is 126 on the Davidson and 120 on the Medici. Is the 120/126/130 measured inner dopout face to dropout face, though? Is that everyone's standard. Because I have heard tell that others measure rear spacing by the C/L of dropouts.

I just want to be sure when I get it spread to 126, which is my intention. I will have no problem shifting the Narrow Six over to the replacement wheelset as that wheelset is designed for a six-speed already. I'm assuming it will slide right into the frame once I have it spread.

I was just very, very surprised that an American frame made in 1979 would have an already-outmoded rear spacing built-in from birth. If anything, I'd think they would be pushing the next best thing.

Thanks for all the replies and info, folks. I'll be tweaking the frame and not feeling too badly about it, either.

DD

Salamandrine 

Yes. Inner dropout face to inner dropout face.

It was very normal for a racing bike to come spaced for 5 spd 120 in 1979, though it was a transitional time.

Drillium Dude 

It's a SunTour. I had to get out my loupe to be sure, but Maeda Industries/Suntour is stamped on the body. Also I. ID, VE are stamped into the lockring.

DD

ThermionicScott 

"VE" would date it to May 1979.

Drillium Dude 

Ah, cool - thanks for that tidbit. I will assume that means it was originally specced to the bike (I'm only the second owner). I will have to look over the receipts provided when I bought the bike and see what the true story is...

...aaand, a receipt dated February 21, 1980 lists the FW as an ST Ultra 6 Win. 13x24. Retail was $22.47.

DD

dddd

I remember back then there was less than unanimous acceptance of wider freewheels due to concerns of the chain angle, so some builders or customers may have felt that U-6 was superior to std-6 spacing.
As well, the revolutionary, bushingless Sedisport arrived around this time, was narrower-spaced to suit narrow cog spacing and was more flexible which lessened noise and power loss associated with cross-chaining.
So (theoretically at least) U-6 had a lot going for it, in addition to it performing well and being utterly reliable. It was quickly followed by U-7 around 1979, which put Suntour several years ahead of their arch-competitor's offerings in terms of gearing spread.


A couple of datapoints here:
Using narrow chain, rear axle spacing can leave as little as 3mm of axle locknut protruding past the outer face of the smallest cog. This is also dependent on frame configuration as in seatstay attachment profile, and on smallest cog size.
Additional locknut protrusion may be needed to clear any inwardly-protruding claw-mount derailer hanger or axle spacer hardware that can contact the chain or freewheel.
I've used standard-spaced 6s freewheels on 120mm French hubs with only 1 or 2mm washer added to the driveside axle spacing, but other brands of hubs (such as Campagnolo) often didn't leave so much unused locknut protrusion on their (ostensibly 5s) 120mm hubs.

jimmuller 

DDude, you measure the spacing as the average between the alpha and beta surface, minus the square of the singulum diameter times PI, accounting for the crossover position of course. Except on Tuesday.

I've seen different FW with different amounts of offset between the locknut surface and the outer edge of the sprockets. The result was that even with nominally identical spacing one could be fit into the bike and the other couldn't. (Unfortunately the one I wanted was the one that didn't fit.) I've also seen bikes where the chainstay protruded different amounts on the inside of the DO.

pastorbobnlnh 

Mystery solved, DD. Great work C&V!

Drillium Dude 

Hmmm...that's strange. As soon as I started to read this I felt the beginnings of a headache; wonder what's up with that?

As for the bold portion: I've seen this a lot over the years, too. In all previous cases it was only a couple/three millimeters difference and I could always spread the rear end enough by hand to fit a slightly-wider wheel. A bit of a PITA, but workable.

DD