Q-factor question
02-11-05 | 10:07 AM
#1
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From: Bay Area CA
I'm wondering if there is an "average" or normal Q-factor for compact and double cranks. I'm thinking of making the move from Shimano 105 triple to compact but I can't seem to find the Q-factor numbers on some of the cranks, like the Ritchey WCS compact and others. Thanks.
Last edited by powpow; 02-11-05 at 10:20 AM.
02-11-05 | 12:18 PM
#2
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Joined: Mar 2003
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From: Grand Prairie, TX
About the only place to find current "Q" numbers is in a current Rivendell catalog or perhaps at their website.
A double will save you about 9mm of "Q" in comparison with a triple, as long as you change the crankset and the BB spindle.
Once you have decided to use STI and use production margins, there are few ways left to reduce Q. Here's why:
1. You have to have margin to drop the chain between the inside ring and the chainstay. Otherwise, with soft materials, and to a lesser extent with steel, the chain will remove material from the chainstay.
2. STI requires certain spacing between the rings.
3. STI requires certain minimum spacing between the outside ring and the inside edge of the crankarm to allow for the function of the FD.
So the only ways to reduce crankset "Q" with STI, after the number of rings is set, is to 1) reduce the margin between the inside ring and the chainstay below production margins, or 2) to find a crankset with laterally thinner crankarms (never heard of such a thing, but why not? With high-technology materials it should be possible), or 3) offset the pedal centers by running the margin on the left side down to zip (no chain there, possible fit symmetry issue for some people, though). It turns out that shoe dimensions tend to prevent reduction of pedal Q. Any reduction of pedal effective spindle length tends to run the inside of the shoe into the crankarm.
A double will save you about 9mm of "Q" in comparison with a triple, as long as you change the crankset and the BB spindle.
Once you have decided to use STI and use production margins, there are few ways left to reduce Q. Here's why:
1. You have to have margin to drop the chain between the inside ring and the chainstay. Otherwise, with soft materials, and to a lesser extent with steel, the chain will remove material from the chainstay.
2. STI requires certain spacing between the rings.
3. STI requires certain minimum spacing between the outside ring and the inside edge of the crankarm to allow for the function of the FD.
So the only ways to reduce crankset "Q" with STI, after the number of rings is set, is to 1) reduce the margin between the inside ring and the chainstay below production margins, or 2) to find a crankset with laterally thinner crankarms (never heard of such a thing, but why not? With high-technology materials it should be possible), or 3) offset the pedal centers by running the margin on the left side down to zip (no chain there, possible fit symmetry issue for some people, though). It turns out that shoe dimensions tend to prevent reduction of pedal Q. Any reduction of pedal effective spindle length tends to run the inside of the shoe into the crankarm.
02-11-05 | 12:45 PM
#3
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Senior Member
Joined: Jan 2005
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From: Bay Area CA
Good answer, thanks. How do you accurately measure Q-factor? Or, since I'm at work right now, does anyone know what the Q is for a Shimano 105 triple? The crank I'm thinking about has a Q of 146mm, and I want to know what the difference will be.
02-11-05 | 12:48 PM
#4
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Originally Posted by SDS
About the only place to find current "Q" numbers is in a current Rivendell catalog or perhaps at their website.
A double will save you about 9mm of "Q" in comparison with a triple, as long as you change the crankset and the BB spindle.
Once you have decided to use STI and use production margins, there are few ways left to reduce Q. Here's why:
1. You have to have margin to drop the chain between the inside ring and the chainstay. Otherwise, with soft materials, and to a lesser extent with steel, the chain will remove material from the chainstay.
2. STI requires certain spacing between the rings.
3. STI requires certain minimum spacing between the outside ring and the inside edge of the crankarm to allow for the function of the FD.
So the only ways to reduce crankset "Q" with STI, after the number of rings is set, is to 1) reduce the margin between the inside ring and the chainstay below production margins, or 2) to find a crankset with laterally thinner crankarms (never heard of such a thing, but why not? With high-technology materials it should be possible), or 3) offset the pedal centers by running the margin on the left side down to zip (no chain there, possible fit symmetry issue for some people, though). It turns out that shoe dimensions tend to prevent reduction of pedal Q. Any reduction of pedal effective spindle length tends to run the inside of the shoe into the crankarm.
A double will save you about 9mm of "Q" in comparison with a triple, as long as you change the crankset and the BB spindle.
Once you have decided to use STI and use production margins, there are few ways left to reduce Q. Here's why:
1. You have to have margin to drop the chain between the inside ring and the chainstay. Otherwise, with soft materials, and to a lesser extent with steel, the chain will remove material from the chainstay.
2. STI requires certain spacing between the rings.
3. STI requires certain minimum spacing between the outside ring and the inside edge of the crankarm to allow for the function of the FD.
So the only ways to reduce crankset "Q" with STI, after the number of rings is set, is to 1) reduce the margin between the inside ring and the chainstay below production margins, or 2) to find a crankset with laterally thinner crankarms (never heard of such a thing, but why not? With high-technology materials it should be possible), or 3) offset the pedal centers by running the margin on the left side down to zip (no chain there, possible fit symmetry issue for some people, though). It turns out that shoe dimensions tend to prevent reduction of pedal Q. Any reduction of pedal effective spindle length tends to run the inside of the shoe into the crankarm.
02-11-05 | 06:03 PM
#6
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Joined: Sep 2002
Posts: 3,695
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From: NC
the q-factor for the ritchey WCS compact is 143mm. same for the 130 BCD cranks. I measured my 105 double at 145...not a whole lot of difference.
105 double and triple are the same cranks, essentially, the triple just has holes for the granny ring to be screwed in, then its mounted on a longer BB. so, find the diff in spindle length and add it to 145 mm. I know the double is 109.5mm, not real sure off the top of my head what the triple BB length is.
105 double and triple are the same cranks, essentially, the triple just has holes for the granny ring to be screwed in, then its mounted on a longer BB. so, find the diff in spindle length and add it to 145 mm. I know the double is 109.5mm, not real sure off the top of my head what the triple BB length is.
