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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 |
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Usable gears on 53,39 x 25,12 9 speed?
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 (_)/ (_) | |
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Usable gears on 53,39 x 25,12 9 speed?
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. |
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Usable gears on 53,39 x 25,12 9 speed?
"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. |
#5
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Usable gears on 53,39 x 25,12 9 speed?
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" |
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