Bicycle Mechanics - Possible only one 46 chainring, 11/36 rear cogs?
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06-03-10, 11:09 AM
Hello, I would like to ask you if you think it would be doable to mount a setup with only one chainring, 46 or 44 tooth, with a 9 speed 11/36 (or 11/34) casette and a SGS rear derailleur in a 700c road bike with flat handlebar. I've thought just in removing the biggest chainring in my compact crankset, so I would remove also the front derailleur and the front shifter, cheers.
Edit to clarify my biggest concern is the possible high cross-chaining.
yes, it's possible.
you might want to keep the FD on there to make it act as a chain keeper.
otherwise it'll be nice to have a dog fang chain keeper and bash guard.
this will be up to user preference, but 11-36 and 11-34 have huge jumps in gears, making you wander between two gears.
06-03-10, 11:21 AM
I agree with AEO. It's doable and if you choose your chainline properly it shouldn't be too hard on the chain at either extreme.
The overall gear range should be adequate for many riders, 108 -112 gear-inches as the high and 33 - 35 gear-inches as the low depending on exactly which cassette and chainring you choose. However, as AEO further said, the gearing gaps will be very large even with a 9-speed cassette.
06-03-10, 04:24 PM
This is no biggie. Make sure your front chainring is lined up with the centerline of your cassette so the chain doesn't sway too far one way or another and it shouldn't jump off. I used a Shimano Nexus crankset ($25 new on ebay, square taper Hollowtech) with a built in chain guard around the single 46t ring on a previous build; I liked it so much I built my new fixie around it and rebuilt my road bike with a flatbar also. I'd like to see your flatbar/lever/shifter setup when you are done..
06-03-10, 04:49 PM
I'm not quite doing what you're considering as there's hills around here. But I went with a single 36T ring and a bashguard for my light duty trail and local market errand ride. It's got 8 speeds out back which is more than enough.
If you're living in a really flat area a 44 or 46 would be a nice road bike single ring and it's perfectly doable. But to help center the ring you'll want to move it to the inside or center position so it lines up wiht the middle of the cassette. That will avoid any issues with cross chaining. And from my roughly 7'ish years of riding my single front gear bike you can forget about the need to keep the FD as a chain guide. I can't remember a time when the chain jumped ship. Although the bash guard MAY have kicked it back into place here and there. But it's never jumped off the inside either. Or if it has the time was so long ago and so infrequent that it's lost in the dust of my mind. When I first did this I was worried that the tooth profiles and ramps would encourage the chain to jump. But it never did. What DID happen due to the tooth profile was that the ring wore out fairly quickly for the amount that I rode it. The replacement was a slightly cheaper non ramped Black Spire ring that has full profile teeth. That ring has been going strong for about 5 years now with little or no sign of wear. So keep that in mind for later.
06-04-10, 12:43 AM
Thank you very much to all. So, in the case of a standard Shimano compact crankset, by just removing the big chainring would let the small chainring too close to the bottom bracket, wouldn't? Would I need then some washer to center it, of those that you have to mount for a triple crankset? I think this perhaps would do that the chain would jump to the inside. There are square taper cranksets of different spindle size, would a longer type avoid this jump?
I live in a very hilly area, but I have in mind this is my second bike, I have another full road bike. A 46/34 setup would be a bit easier than a 34/25, enough for most of the hills, the main disadvantage is the 46/11 would force me to coast some more in descents, not much, in flat I can only move a 50/14-15, equivalent to 46/13. I really don't mind very much the two teeth jump between gears, I already have done lot of miles with it, mainly using only one chainring. I mounted the bike with the flat handlebar and the 9 speed rear casette and long derailleur some time ago.
Taxi Rob, my setup wouldn't be really a work of art, but if I success I will post some picture.
06-04-10, 08:45 AM
These setups typically don't work as well in practice as they do in theory, because of chainline. Two chainwheels tend to be more reliable than just one.
I never quite understood the dislike for double chainrings. Triples, I can understand, because no-one wants to bring "granny" along on their super-fast bikes. But doubles? To each their own, I suppose, so good luck. If it was me (and it's not, so feel free to utterly ignore) I'd think about something like a 50T inner, so as to do that half-step gearing. [Me, I prefer the closer gears out back, but it's not for everyone, I guess.] To deal with the large gear steps, that is.
On my wife's triple, it has a plastic nub near the inner ring, to keep the chain from falling off (inspite of having the FD). That would be less visible than a FD left on for the same purpose.
Is this to set up for a minimalistic commuter?
06-04-10, 12:31 PM
Single chainrings are appealing because, in theory, they are half as complicated as double chainrings. This is not so much because of the extra chainring but because of the front derailleur and shifter. But front derailleurs don't break nearly as often as rears. Rear derailleurs get broken or bent from being hit in self-closing doors or laying the bike down or being hit by bikes or clumsy feet. The front derailleur is in a less vulnerable place on the bike.
06-04-10, 02:26 PM
I am running a single for my commuter, 39 ring, 11/25 cassette I think. It gives me enough for some hills on my route, and still about to push low 20's on the flats. I thought I would need something in the 44 range but so far so good. I dropped the chain a few times shifting to quickly but after shortening the chain up this hasn't happened.
06-06-10, 10:32 AM
I've made the preliminary test with an awful result: at home, setting the bike, the 46 chainring has some screws, one of them in the inner side rubbed with the rear drop of the frame (sorry for my language), so I filed it and it appeared to work well, but in the road, after two or three hundred meters, I began to hear that horrible sound again, so I'm afraid that the 11-36 rear bends in some way the front compact crank, or only the chainring. I guess that with two chainrings the crankset is stronger, but I'm not sure if that it's only that the 46 chainring is really of bad quality, I'll make this afternoon more tests. I don't know either if the chainring is purposed only to be the biggest in a compact crankset, it didn't indicated nothing in the box. I've tried also to put the chainring in the biggest position, but there the chain slides to the left, and jumps off the chainring. I'll try to see also if a 11-34 makes not so much strength in the set, the 11-36 casette was really at first a 12-36, I just removed the 12 and put instead the 11, perhaps this has to do something with it, as well.
I've decided to setup the bike so because I'm really fed up of the chain rubbing against the front derailleur, and taking time to set it, also to gain some weight. But If I can not to do it, I'll have to get back to the compact with the laborious (for me) front derailleur again, I'm afraid.
I've just realized that I've installed the bottom bracket without washers between the crank side and the frame, and it seems it needs at least one, I first installed it with two, but I had problems tightening the BB wheel, so I removed both. I will install it with one only and hopefully fix the problem.
06-08-10, 03:11 AM
In the event of someone remain interested, today I've done a very pleasant ride of 31 miles (50 km.) including 2.465 feet total ascent (750 mts.), averaging 15,3 miles/hour (24,5 km/h). The bike, as shows in the pictures, has a weight of 20 pounds (9 kilos).
It's wonderful the comfort in the shifting. It's only: steeper, one touch up, less steep, one touch down. I can forget at last the two cogs up or down shifting the chainrings. With this setup, 46 front, 36-12 rear, for me (almost half the value than a pro, climbing), I can climb a 9% grade without problems, so I'll change now to 34-11, and in a future, will shift to 10 speed, 36-11. Even with 46-12, the coasting is not so excessive as I was afraid of.
The bike, as you can see, it's not very pretty, actually some ugly, but I ride looking ahead, I don't see it riding and I ride alone, so I really don't mind at all, as long as she does what I ask her. Cheers.
Sorry I can't post pictures, as it seems. And a second edition because the pictures were too big, I've updated the links.
Sounds great to me! We have lots of short (but steep) hills around here, and I think we average a bit less climbing per mile. But I get similar average speeds, so now I don't feel too bad. ;) Only, 9% climbs tend to make think of walking, thankfully those are few and far inbetween...
06-08-10, 11:23 AM
I've thought just in removing the biggest chainring in my compact crankset, so I would remove also the front derailleur and the front shifter.
So after you do that what do you think you will have accomplished?
06-08-10, 02:35 PM
If by accomplish you mean a big achievement, I don't think so, but I have now a more clean bike, without some artifacts that I think are not very aero-dynamic, I have less weight: front derailleur, two chainrings (50+34) instead of one alone, a wire less, and the front shifter. I haven't to worry about setting the front derailleur, about the noise rubbing against the chain. In fact, if the Rohloff system wasn't so heavy and expensive, I would go to that now. And I really don't know for certain, but maybe the chain works less now too. Of course, I've lost some gears, not 9, because some were repeated anyway, but really I don't see another lost thing.
(Sorry, yes, some more coasting apart).
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