Usable gears on 53,39 x 25,12 9 speed?

"chris_gr" wrote in message
...
Billx wrote:
On a new Shimano Ultegra transmission with 53,39 up front and 12-25 9
speed rear how many gear combinations should I expect to be possible
without derailer/chain rub? Right now the 39 will only run 4-5 of the
9
rear gears without rubbing and the bike is brand new. Suspect the shop
hasn't adjusted the derailerst beyond factory settings and that a
greater gear range is possible.



I was also wondering which combos are un-usable. I have a tribike with
650 wheels and 55/42 front and a 11-23 in the back. When in the 42-12
combo the chain rubs the 55T ring. I thought it was unusual to have 2
noisy cogs in the back but from this discussion it sounds pretty normal.


You should always avoid big/big and small/small combos. Bad for things...
That rubbing sound y'all hear is the chain rubbing on the either the big
ring or the outer cage of the f. der. Sometimes it is an adjustment thing,
most often people are riding in gears that their bike doesn't like...

There are overlapping gears in your c-ring/cassette. I generally shift down
a few (3-4) cogs while in the small ring, then shift to the big ring and
back up a gear or two to get roughly the same gear I was just in. Once you
get past the middle (going towards physically smaller gears) of the
cassette, its better to be in the big ring. Vice versa when you're going
back up the cassette.

So, to answer the specific question you'll have to go look up a gear inch
chart to see exactly how many discrete gears there are after removing
overlap.

Having said that, if you surf on over to Sheldon Brown's site, he probably
explains everything over there a lot better than we're going to...

That help?

Mike

On Sat, 27 Sep 2003 01:14:07 +0950, chris_gr wrote:

Billx wrote:
On a new Shimano Ultegra transmission with 53,39 up front and 12-25 9
speed rear how many gear combinations should I expect to be possible
without derailer/chain rub? Right now the 39 will only run 4-5 of the
9 rear gears without rubbing and the bike is brand new. Suspect the
shop hasn't adjusted the derailerst beyond factory settings and that a
greater gear range is possible.

So, it's the chain rubbing on the derailleur cage? That is an adjustment
or user error. Most new Shimano, and all Campy, front shifters have some
trim adjustment -- a mini-click that does not move the chain, but moves
the cage a bit to better center it around the chain. If that doesn't
help, talk to the shop people.

I was also wondering which combos are un-usable. I have a tribike with 650
wheels and 55/42 front and a 11-23 in the back. When in the 42-12 combo
the chain rubs the 55T ring. I thought it was unusual to have 2 noisy cogs
in the back but from this discussion it sounds pretty normal.

Well, this is more normal. You might be able to avoid it by adding
spacers between one of the rings and the spider. But you have to be
careful, too much space and the chain could get snagged in between. But
the small-second smallest combination is probably the same ratio as a more
reasonable combination with the big ring.

--

David L. Johnson

__o | "What am I on? I'm on my bike, six hours a day, busting my ass.
_`\(,_ | What are you on?" --Lance Armstrong
(_)/ (_) |

Sounds about right,
You can calculate the gear inches, or use Sheldon Brown's gear calculator.
http://www.sheldonbrown.com/gears/
Once you see the chart, you probably only need to use the 19- 25 with the
39t.
You shouldn't have a problem with chain/derailleur rub unless you go beyond
this.
At least I don't with my 53/39 Ultegra 12-27 9sp.
-tom


Billx wrote:
On a new Shimano Ultegra transmission with 53,39 up front and 12-25
9
speed rear how many gear combinations should I expect to be possible
without derailer/chain rub? Right now the 39 will only run 4-5 of
the
9 rear gears without rubbing and the bike is brand new. Suspect the
shop hasn't adjusted the derailerst beyond factory settings and that
a
greater gear range is possible.

"Mike S." mikeshaw2@coxDOTnet wrote in message


You should always avoid big/big and small/small combos. Bad for things...
That rubbing sound y'all hear is the chain rubbing on the either the big
ring or the outer cage of the f. der. Sometimes it is an adjustment
thing,
most often people are riding in gears that their bike doesn't like...

There are overlapping gears in your c-ring/cassette. I generally shift
down
a few (3-4) cogs while in the small ring, then shift to the big ring and
back up a gear or two to get roughly the same gear I was just in. Once
you
get past the middle (going towards physically smaller gears) of the
cassette, its better to be in the big ring. Vice versa when you're going
back up the cassette.


That depends on the terrain you live in (and the gears you are using). I
found that since I moved to this area with rolling terrain, I wanted to be
in the big ring most of the time and I am using the 9 smallest cogs (on a
10v system). before I moved, I lived near the coast and was either on flat
terrain or climbs of at least 4 percent. While there, my habits were about
as you descibed. The same comments apply to a race course that is rolling,
vs all flats or with climbs.

The bottom line is that a road bike should be able to use all but the
big\big and small\small. The Camag 10v systems are so smooth, you can use
the big\big without noticing any additional roughness, although that does
not make it a good idea. I am just pointing out that someone oly expecting
to use 5 cogs per ring has set his or her sites too low.

Chris- When in the 42-12
combo the chain rubs the 55T ring. BRBR

No surprise there. If you start form a stop light in third gear in tyour car,
it won't work well either. Shift into the big ring and up a few cogs to get
the same ratio, w/o noise.

Peter Chisholm
Vecchio's Bicicletteria
1833 Pearl St.
Boulder, CO, 80302
(303)440-3535
http://www.vecchios.com
"Ruote convenzionali costruite eccezionalmente bene"