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#1
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triple chain line question
Hi folks,
Is it possible to rig a triple crankset such that the large ring has okay chainline to all the cogs and only the middle and lower are restricted? If so, how many cogs could I expect to lose due to chainline issues on the middle and lower rings? I measured my current triple, and while the derailer cage itself has 7-8mm to go before it bumps the seat tube, there is a roller with only 1-2mm left. Many thanks, Reid |
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#2
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triple chain line question
On 2007-05-20, Reid Priedhorsky wrote:
Hi folks, Is it possible to rig a triple crankset such that the large ring has okay chainline to all the cogs and only the middle and lower are restricted? If so, how many cogs could I expect to lose due to chainline issues on the middle and lower rings? I measured my current triple, and while the derailer cage itself has 7-8mm to go before it bumps the seat tube, there is a roller with only 1-2mm left. You'll need to move the crankset inwards by using a BB with a shorter spindle. I think you'll find the biggest problem in doing this isn't the deraileurs, but the inner chainring rubbing the right chainstay. Cheers Joel -- Human Powered Cycles | High quality servicing | Low cost 2nd hand bikes www.humanpowered.com.au | Bicycle re-use centre |
#3
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triple chain line question
Joel Mayes wrote:
On 2007-05-20, Reid Priedhorsky wrote: Hi folks, Is it possible to rig a triple crankset such that the large ring has okay chainline to all the cogs and only the middle and lower are restricted? If so, how many cogs could I expect to lose due to chainline issues on the middle and lower rings? I measured my current triple, and while the derailer cage itself has 7-8mm to go before it bumps the seat tube, there is a roller with only 1-2mm left. You'll need to move the crankset inwards by using a BB with a shorter spindle. I think you'll find the biggest problem in doing this isn't the deraileurs, but the inner chainring rubbing the right chainstay. Cheers Joel I think this setup would want a longer range mountain bike dérailleur in the rear to cover the extra range. I tried a 22-36-58 front with a 14-39 rear (Antique Sun Tour Alpine gear) and found that at the limits the chain was either way loose (22/14) or bound up (58/39), even though those gears don't make much sense. It was Ebay's fault for putting such tempting bike stuff up there. Off set is a real problem since I have found at least 3 different offsets on square mount crank sets. I have one that is a real odd duck that has the square hole turned 45 degrees from the normal. If you want to experiment, spend a little on some stuff from Ebay, but be careful to ask if the individual chain rings are changeable and not just a Chinese tack weld. Ride, mechanic, ride some more, repeat. Bill Baka |
#4
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triple chain line question
On 2007-05-21, Bill wrote:
Joel Mayes wrote: On 2007-05-20, Reid Priedhorsky wrote: Hi folks, Is it possible to rig a triple crankset such that the large ring has okay chainline to all the cogs and only the middle and lower are restricted? If so, how many cogs could I expect to lose due to chainline issues on the middle and lower rings? I measured my current triple, and while the derailer cage itself has 7-8mm to go before it bumps the seat tube, there is a roller with only 1-2mm left. You'll need to move the crankset inwards by using a BB with a shorter spindle. I think you'll find the biggest problem in doing this isn't the deraileurs, but the inner chainring rubbing the right chainstay. Cheers Joel I think this setup would want a longer range mountain bike dérailleur in the rear to cover the extra range. I tried a 22-36-58 front with a 14-39 rear (Antique Sun Tour Alpine gear) and found that at the limits the chain was either way loose (22/14) or bound up (58/39), even though those gears don't make much sense. It was Ebay's fault for putting such tempting bike stuff up there. I think the OP wanted to be able to use all the rear cogs with the outside chainring while maintaining a reasonable chainline. Nothing was said about the size of the rings being used (could be running 36,37,38 chainrings for all we know). Cheers Joel -- Human Powered Cycles | High quality servicing | Low cost 2nd hand bikes www.humanpowered.com.au | Bicycle re-use centre |
#5
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triple chain line question
On Mon, 21 May 2007 09:26:29 +0000, Joel Mayes wrote:
I think the OP wanted to be able to use all the rear cogs with the outside chainring while maintaining a reasonable chainline. Nothing was said about the size of the rings being used (could be running 36,37,38 chainrings for all we know). Yes, something like 46-36-24 with a 12-34 or somesuch in the back. Right now I have 52-42-30, and with an 11-32 in the back I don't have too much use for the 52-tooth chainring, but a lower granny would be great. I guess the main question is, how can I know how short a BB I can get away with before buying one and trying it out? Thanks and take care, Reid |
#6
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triple chain line question
On 2007-05-22, Reid Priedhorsky wrote:
On Mon, 21 May 2007 09:26:29 +0000, Joel Mayes wrote: I think the OP wanted to be able to use all the rear cogs with the outside chainring while maintaining a reasonable chainline. Nothing was said about the size of the rings being used (could be running 36,37,38 chainrings for all we know). Yes, something like 46-36-24 with a 12-34 or somesuch in the back. Right now I have 52-42-30, and with an 11-32 in the back I don't have too much use for the 52-tooth chainring, but a lower granny would be great. I guess the main question is, how can I know how short a BB I can get away with before buying one and trying it out? Thanks and take care, Reid Measure the current clearnance + current BB length and do some math :-) There are two many variables to get an answer here You do need to think about why you want to do this though, I can't see any advantage in using the outer chainring of a triple predominately. Cheers Joel -- Human Powered Cycles | High quality servicing | Low cost 2nd hand bikes www.humanpowered.com.au | Bicycle re-use centre |
#7
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triple chain line question
Joel Mayes wrote:
On 2007-05-22, Reid Priedhorsky wrote: On Mon, 21 May 2007 09:26:29 +0000, Joel Mayes wrote: I think the OP wanted to be able to use all the rear cogs with the outside chainring while maintaining a reasonable chainline. Nothing was said about the size of the rings being used (could be running 36,37,38 chainrings for all we know). Yes, something like 46-36-24 with a 12-34 or somesuch in the back. Right now I have 52-42-30, and with an 11-32 in the back I don't have too much use for the 52-tooth chainring, but a lower granny would be great. I guess the main question is, how can I know how short a BB I can get away with before buying one and trying it out? Thanks and take care, Reid Measure the current clearnance + current BB length and do some math :-) There are two many variables to get an answer here You do need to think about why you want to do this though, I can't see any advantage in using the outer chainring of a triple predominately. Cheers Joel I have to side with the math solution since I have seen too many variables on BB length and cranks. A 52/11 is only good at my strength level for extra speed on downhills and even that is questionable. On the flat roads it is good for maybe a really lazy 10 MPH while still building up some strength in the legs. A cadence of only 25-30 is a bit low, but good for those lazy days. Bill Baka |
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