Re: Chain line (non-fixed) and crank axle length

[Pete Biggs]

Retro Bob wrote:
> Just thinking... if you stretch a 120mm frame (assuming you do it
> evenly), you should actually need to move the crank axle out to the
> right (longer right side beyond race or spacer), correct ? In other
> words, even the new, wider spaced frames (126 or 130mm) should have
> axles with longer spindles on the chainwheel side... but unless I
> am reading things wrong, it doesn't seem like this change was made
> by manufacturers (?)

I found the chainrings on a 1980's double crankset (SR?) were indeed too
inboard when I spread the frame from 126 to 130 and changed from a 6-speed
freewheel to a 9-speed Campagnolo cassette. Nevermid small-small, I
couldn't even use the middle of the cassette from the small ring without
rubbing, if I recall correctly. I think the chainrings might have been
closer together than modern rings, as well.

Instead of just getting a longer BB, I upgraded the crankset to a modern
Campag triple and used the default recommended BB for the cranks. This is
all basically fine.

> Second question/theory: In general, a chainline with the chain wheel
> displaced to the right too much is preferred over one displaced
> too much to the left (ideally it is "perfect" but that might require
> buying a crank axle we can't get ? ).
/snip

But the chainline would be perfect only for one sprocket (from each
chainring). Conventional wisdom might dictate "perfect" is the middle of
the cassette, but you might happen to prefer to use one end more than the
middle or the other end.

~PB

 

[Zog The Undeniable]

Retro Bob wrote:

> Last question: Do "new" bikes out of the factory with 9 or 10 speed
> clusters manage to work all the gears without issues due to thinner
> chains and wider frames ? Or do they encounter the same problems at
> the extremes with 'not very usable' combinations ?
>
I'm using a 105 crankset on the recommended BB and a 105 rear hub with
9-speed cassette. It will rub at the extreme combinations but OTOH the
FD never needs trimming in "normal" use.

 

[Bob Wheeler]

I have seen several comments about certain combinations not working, but
this has not been my experience. I have converted two mid 70's frames
using modern components, and both work well in all gear combinations.
There are both tripples, one uses Ultegra, the other Campy Record. To
achieve correct chainline, I offset the rear triangle by 2mm on both and
used the adjusting screws on the rear dropouts to make the wheel track
correctly. This in spite of the fact that the frame using the Campy
Record has a shorer than normal chainstay.


Retro Bob wrote:
> On Sun, 3 Oct 2004 01:39:23 +0100, "Pete Biggs"
> <pblackcherry{remove_fruit}@biggs.tc> wrote:
>
>
>>But the chainline would be perfect only for one sprocket (from each
>>chainring). Conventional wisdom might dictate "perfect" is the middle of
>>the cassette, but you might happen to prefer to use one end more than the
>>middle or the other end.
>
>
> Thank boys. Personally, I typically stay on the large chainwheel and
> do like that to work through the range of rear sprockets. I drop to
> the small chainwheel only in combination with the largest or second
> largest rear cogs for hill climbing (noting that I don't run a very
> large rear sprocket so I need a little gear drop occasionally).
>
> Last question: Do "new" bikes out of the factory with 9 or 10 speed
> clusters manage to work all the gears without issues due to thinner
> chains and wider frames ? Or do they encounter the same problems at
> the extremes with 'not very usable' combinations ?
>


--
Bob Wheeler --- http://www.bobwheeler.com/
ECHIP, Inc. ---
Randomness comes in bunches.