Here's another caveat... The majority of frames that I've checked with Campy, VAR or Park tools since the mid 70s have had misaligned dropouts!
Dropouts even a couple of degrees out of alignment can put undue stresses on the hollow axles of QR hubs.
Stretching 120mm wide dropouts 6mm to fit a 126mm wide 6 speed hub works out to 3mm (slightly under 1/8") per side. Doesn't sound like much but it comes out to 3.6° per side or a total of 7.2° of dropout misalignment when the rear triangle is not cold set and realigned.
Someone check my math please - I drew it up on a CAD program rather than trigging it out so I could be wrong.
Something has to give and it's probably not going to be the dropouts.
The problem with this calculation is that since most dropouts are misaligned there's a slim possibility that stretching the rear triangle to 126mm might bring the dropouts into alignment! ;-)
Another thing to consider is the OLN (over lock nut) width of the hub.
I've seen specs for the following OLN widths on hubs used on single bikes with multiple cog freewheels made during the past 50 years:
117mm (ISO for 3 & 4 speed FW) 118mm 119mm 120mm (standard for 5 speed FW) 121mm (some Campagnolo 5 speed hubs & some Japanese hub) 122mm (ISO for 4 & 5 speed FW) 124mm (some Japanese and French hubs) 125mm (some Campagnolo hubs) 126mm (standard for 6 & 7 speed FW) 127mm 127.6mm (old standard for 6 speed FW) 128mm 129mm 130mm (standard for 7+ speed FW and freehubs) 135mm (standard for MTBs and some newer road hubs)
I pulled these specs out of Sutherland's, manufacturer's literature and other published sources.
I've frequently found the the OLN width has been modified with spacers or washers for whatever reason on many older hubs
The much despised (at least in the CR circle) Shimano SIS indexing system pretty much forced the OLN width standardization to 120mm, 126mm, 130mm and 135mm.
I like to adjust rear dropout widths to 120-121mm for 5 speed FWs and 126-127mm for 6+ speed freewheels. It makes for easier wheel insertion.
Chas. Colerich Oakland, CA USA
Ken Freeman wrote:
> There should be a caveat thrown in here: regardless of Sheldon's research
> and knowledge, cyclists and techs on several forums have thought they had
> bent or broken axles after using a wider wheel in an older frame without
> cold-setting the frame and aligning the dropouts. I don't know any of the
> extenuating circumstances, but it seems one should be cautious about doing
> this. With my NR hubs, I am reluctant to break or stress any original
> axles.
>
> On Tue, Dec 15, 2009 at 5:36 PM, jeff holt <jefflaw@msn.com> wrote:
>
>> Back in the late 70's/early 80's when 6 & 7 speed freewheels & 126mm hub
>> spacing started appearing, we'd routinely install these newer wheels in
>> older frames with 120 mm rear spacing without any ill effects.
>> Below is a quote from Sheldon Brown's website to that effect.
>>
>>
>> "Ideally, the frame spacing should exactly match the hub spacing. This
>> makes for easiest wheel replacement. In practice, however, there's a
>> fair amount of latitude in fit. In fact, when the first 130 mm 8-speed
>> hubs were introduced, they had locknuts with beveled sides, so that you
>> could "spring" apart the rear triangle of a frame made for the
>> then-standard 126 mm spacing.
>>
>> In general, you can safely go up one size in spacing this way, just
>> springing the frame apart. I can't give you an absolute guarantee that
>> this won't cause damage, but the odds are very much in your favor."
>>
>> Jeff Holt
>> West Deptford, NJ
>> USA