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Single Chainwheels (was Re: 12-25 and 12-27 9spd)  

post #1 of 4
Thread Starter 
Hi all,

As I ponder the gearing options available to me with the 13-26 and 13-28 Campy 9 speed cassettes
I've just ordered, a thought occurred to me. My old bike once used a 14-21 tooth six speed
freewheel. That was pretty much de rigueur for racing when I was a teenager, unless you were a
masochist and ran a corncob freewheel - 14-19. Now the gearing range on the 13-26 nine speed
cassette, when used with my trusty 49 tooth TA chainring (thanks Peter) is actually a tad wider than
my old 14-21 with 42/52 chainwheels, with nine steps from 50 to 100 inches. The old 12 speed had 10
useable ratios, similarly spaced, but the 15-42 and 19-52 duplicated the same actual gear.

So why don't I see people running just the one chainwheel? You could lose the front derailleur, one
of the chainwheels (and perhaps use a track crank with 3/32nd track chainwheel), front shifter, and
a pile of cable. And you'd never get the chain rubbing on the front derailleur cage again, as
there'd be no cage to rub on.

Indeed, now that I think about it, "five speeds" were pretty common back in the seventies, but you
never see their equivalent now.

Regards,

Suzy
post #2 of 4

Re: Single Chainwheels (was Re: 12-25 and 12-27 9spd)

In article <Kq59b.102395$bo1.14349@news-server.bigpond.net.au>, Suzy Jackson
<suzyj@bigpond.com> wrote:
>Hi all,
>
>As I ponder the gearing options available to me with the 13-26 and 13-28 Campy 9 speed cassettes
>I've just ordered, a thought occurred to me. My old bike once used a 14-21 tooth six speed
>freewheel. That was pretty much de rigueur for racing when I was a teenager, unless you were a
>masochist and ran a corncob freewheel - 14-19. Now the gearing range on the 13-26 nine speed
>cassette, when used with my trusty 49 tooth TA chainring (thanks Peter) is actually a tad wider
>than my old 14-21 with 42/52 chainwheels, with nine steps from 50 to 100 inches. The old 12 speed
>had 10 useable ratios, similarly spaced, but the 15-42 and 19-52 duplicated the same actual gear.
>
>So why don't I see people running just the one chainwheel? You could lose the front derailleur,

As David Millar recently found out, removing the front derailleur can result in the chain falling
off when the angle gets extreme (ie, when shifting to one end or the other of the cluster).

Search Google for "david millar front derailleur" if you want to see all the coverage.

This is not exactly a revelation since the exact problem is also described in a dog-eared copy of
the Eddie B. Book from the 1980s.

And if you use chainrings with ramps and shaped teeth, such as any current Shimano or Campy road
chainring, the chainring is specifically designed to help the chain fall off as easily as possible.

> one of the chainwheels (and perhaps use a track crank with 3/32nd track chainwheel), front
> shifter, and a pile of cable. And you'd never get the chain rubbing on the front derailleur cage
> again, as there'd be no cage to rub on.
>
>Indeed, now that I think about it, "five speeds" were pretty common back in the seventies, but you
>never see their equivalent now.

Yes and the distance from the first to fifth cogs in back wasn't nearly as far.

--Paul
post #3 of 4

Re: Single Chainwheels (was Re: 12-25 and 12-27 9spd)

> > Suzy Jackson <suzyj@bigpond.com> wrote:

> > >So why don't I see people running just the one chainwheel? You could lose the front derailleur,

"Bruce" <bfrech.SPAMDELETE@spam.erols.com> wrote in message news:bk2v07$akt$1@bob.news.rcn.net...

> I've done that but as another reply mentioned you have to worry about the chain falling of the
> chainring. So leave the front der on and use a single ring.

That doesn't sound right to me. First, the chain will stay on across the whole range of gears on
most doubles and triples, without dropping to another ring, or rubbing on the front derailer. And
the angles when cross-chained on a triple are way worse than with a single chainring.

<rant>There are exceptions, of course, like with my silly fat-tubed Klein that requires an
extra-wide BB to keep the front derailer from bottoming out on the seat tube, causing a bad
chainline that pulls the chain off the big ring when more than 3 gears over. This is a good reason
to avoid aluminum bikes.</rant>

Another exception is with a downhill racing or stunt bike that gets bounced around a lot, but for
these you can get "Rock Rings" and other chainrings/guides to keep the chain firmly seated.

A friend of mine built a really neat commuter bike with one chainring, and a MTB cassette. It has
about the same gearing range as most road bikes' before the 8-9-10 speed era. It's perfect for
anywhere the hills aren't huge. If I lived in some horrible flat place and I was building a bike
from parts, I'd probably do the same thing.

Matt O.
post #4 of 4

Re: Single Chainwheels (was Re: 12-25 and 12-27 9spd)

Suzy Jackson <suzyj@bigpond.com> wrote:

> you'd never get the chain rubbing on the front derailleur cage again, as there'd be no cage
> to rub on.

Others have mentioned the chain drop problem - it's most likely to occur if you hit a bump and the
lower chain run goes slack briefly. So it can be an issue even if you never get chain rub under
normal circumstances.

> Indeed, now that I think about it, "five speeds" were pretty common back in the seventies, but you
> never see their equivalent now.

Yes. Though these bikes generally had narrower rear clusters, un-shaped chainrings (of course
you could still use one today) and a pant guard on the outside, so there was a chainguide on at
least one side.
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