fiataccompli

I'm refreshing/rebuilding a '71 Raleigh Professional & a '75 Schwinn Paramount. Both have more-or-less 120mm rear spacing & both have original wheels with tubular rims. Ultimately, I intend to build new wheels with nice, tasteful clinchers on the original hubs for each bike...but for now, i'm planning on setting up a rear wheel that was orignally set up with 126mm spacing that I will run on both bikes while. Having a slightly narrower freewheel (the Paramount came with a nice 'ultra' spaced 6 speed freewheel) and using narrower spacers to get to the 120(ish) spacing is easy...but it looks like a bit of re-dishing will be in order (which I suppose is to be expected). My question is whether there is any sort of 'standard' width difference between a hub from the 120mm era vs. the 126mm era...on the Ofmega hub I'm going to run compared to the Campy Nuovo Record hub, there's maybe a 1mm difference in width from cap to cap (at least with rather hurried measurement last night). insight?

Michael Angelo 

Always redish the wheel after setting the hub width. Making sure you're left with enough spoke length toProperly engage the spoke nipple.

dddd

You could also just take out the washer from both ends of the 6-speed hub, and there would likely be enough clearance with even a standard 6-speed freewheel if you use a modern 8sp chain.

The axle might neet to be shortened a bit to allow room for both of the cone springs to be fully compressed under the ends of the quick release skewer, or you could set the springs aside, but do try to make the two ends of the axle protrude identically from the locknuts.
The resulting ~122mm width axle will fit nicely in the older frame with no re-dishing.

If your locknut gripping surface is at least 3.3mm beyond the outer surface of the smallest cog's teeth, there is normally enough room between the freewheel and frame for the chain (using modern chain). Keeping this distance to a minimum as will be the case makes for a less-easily bent or broken axle btw.

repechage

On a rear hub one key dimension is the drive side locknut face to the freewheel land. I try always to make those as close as possible, +/-m.5 mm with one brand of hub its relatively easy. This was for way back when I could run one brand of freewheel, exchange them and not have to adjust the rear shift limits.

An Ultra Six often likes 122 mm best. It really depends on how the inside surfaces of the drive side stays are finished off.

Forcing a 126 mm rear wheel into a narrower frame can be done, but I am not a fan of it.

If you play with the axle spacing, be sure to adjust the wheel dish.

3alarmer 

I do not understand your question ? Are you talking about the dirt caps
that fit in the bearing races as the distance in question ?

If that is the dimension you are asking about, then no, no standard
of which I am aware..............

dddd

"An Ultra Six often likes 122 mm best. It really depends on how the inside surfaces of the drive side stays are finished off."

That was my experience with the 5-speed hubs, I would add a 1mm washer to each end, and with the U-6 freewheel and proper narrow chain, it would normally clear the frame, especially with a smaller 13t cog.

Starting with a 6, 7 or 8-speed hub, I've always been able to take a mm or two in washers off of each end and still get the chain to clearthe frame. A standard 6-speed freewheel is about 2mm narrower than a 7-speed, so a symmetric narrowing of a 6-7-speed hub axle to 122mm usually is a go.

Some old bikes with ~120mm, 5-speed Normandy hubs were so dished that the axle would take a regular 6-speed straight away. There was such a huge gap between the 5-speed freewheel and the frame that even the old wide chain could fall to the axle!
Schwinns and Peugeots come to mind here.

pat5319

The 126 hubs have longer axle and wider or extra spacer on drive side to accomodate more gears
I've switched many bikes and hubs from 120 to 126

fiataccompli

I know I could re-space the frames, but in the end I shouldn't really need to. I was asking (per the question a few replies up) about I suppose a dust cap to dust cap type measurement...ie, the machined width of the hub assembly w/o axle. In my case, thinking further I realized I didn't have much leeway on the non-drive side to work with (just a cone & lock washer) so to get about 5mm narrower I had to reduce the spacer width on the drive side...so, I can re-dish,but I guess I was wondering of a hub from the 120mm era would simply be 4-5mm narrower from cone to cone if that makes any sense. No worries, this is something I can figure out as easily just by feel with spares in my workshop and re-dishing was part of what I figured.

repechage

The hub shell and the "cone to cone" dimension will be the same for a typical 120 mm to 126 mm dimensioned hub.
There are a few exceptions but they are rare and often French.