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Ideal Q-Factor

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Ideal Q-Factor

Old 08-17-10, 10:04 AM
  #1  
krazygl00
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Ideal Q-Factor

I only recently learned about the new BB30 standard, and it is pretty interesting. I think sometime in the future when I'm doing a new build I may seriously consider going for a frame using BB30. This got me thinking about Q-Factor (distance between the pedals measured along the crank axle; basically, how far your feet are apart as you pedal), since one of the benefits of BB30 is reduced Q-Factor.

What would be the ideal Q-Factor, if you could choose anything from common modern cranksets to a hypothetical zero (feet spinning right next to each other with zero distance between them)? It seems like zero would result in optimal efficiency for the machine, ie. least possible frame-flex, more power transferred to the drivetrain, but would that zero number be best for the human pedalling it? It seems like most athletic stances have the feet placed at a very natural shoulder-width.

In other words, if you had a magical drivetrain* with a zero Q-factor, would it be the best overall?

*Note I am not trying to invent a magical drivetrain.
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Old 08-17-10, 10:12 AM
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I've thought about this before.

Who decided that a narrower Q-Factor was better? I've never seen any power data to back this up (and would like to see some) yet there seems to be a constant drive towards narrower and narrower spec.

Frankly, I have my cleats adjusted to give me a slightly wider Q-Factor because it feels far more comfortable and I certainly don't have birthing hips.
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Old 08-17-10, 10:16 AM
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The bike fitter used washers to move my pedals out a bit further. I think it depends on the person. With a narrow Q factor built in, you can always move the pedals back out (longer pedal axles, washers or spacers) but with a wider Q factor you can't make things narrower - so a narrow Q factor crank should give the most flexibility setting up the bike.

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Old 08-17-10, 12:14 PM
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Crank on cranks (Grant Peterson): https://www.rivbike.com/article/components/cranks
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Old 08-17-10, 12:18 PM
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Originally Posted by krazygl00 View Post
since one of the benefits of BB30 is reduced Q-Factor.
That's what I thought too, think again. FSA at least doesn't advertise a narrower Q, just more ankle clearance. You can't get too narrow as the chainstays get in the way. I'm just saying that the narrower Q factor promised by BB30 isn't really all that narrower in general.
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Old 08-17-10, 12:20 PM
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Dunno. I got my TT bike to ~126 I think, but I only did that because it's allegedly more aero.
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Old 08-17-10, 12:25 PM
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Some of the BB30 cranks don't have any narrower Q-factor than their external BB counterparts.

Cannondale Si and SiSl cranks do have a nice narrow Q-factor though, and the Specialized cranks are like 146-147mm.

The Sram BB30 cranks don't have any narrower Q-factor, just more heel/ankle clearance.

Q-factor is a very personal thing and is best assessed during a professional fit.

Most cranks are in a neutral enough position to let you get your feet where they need to go by moving the cleats from side to side, or washer (if you need to go wider). There are some exceptions though. I can't ride Sram cranks, because they are too wide even with my cleats moved outward all the way. Shimano cranks will work though and Campy/Fulcrum are just about perfect for me.

YMMV.
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Old 08-17-10, 12:27 PM
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Originally Posted by ElJamoquio View Post
Dunno. I got my TT bike to ~126 I think, but I only did that because it's allegedly more aero.
That's pretty much all I can come up with for any reason why a narrower Q-factor might be beneficial.
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Old 08-17-10, 01:03 PM
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Originally Posted by briscoelab View Post
Specialized cranks are like 146-147mm.

The Sram BB30 cranks don't have any narrower Q-factor, just more heel/ankle clearance.

.
This contradicts with what I've read.
Specialized's Road BB30 Fact Crankset has a q-factor of 138.5mm as measured by one of their sponsored triathletes.
Sram's BB30 has a 145mm q-factor - which isn't narrower than most but is narrower than their 150mm GXP style cranks.

As a lot of people here have said, it's personal. I rode a 130mm setup on my tri bike for a while and liked it quite a bit but it isn't that much different than 145 on my road bike.
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Old 08-17-10, 01:09 PM
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Originally Posted by ElJamoquio View Post
Dunno. I got my TT bike to ~126 I think, but I only did that because it's allegedly more aero.
It's the sh*t that kills.
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Old 08-17-10, 01:14 PM
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Originally Posted by Triguy View Post
This contradicts with what I've read.
Specialized's Road BB30 Fact Crankset has a q-factor of 138.5mm as measured by one of their sponsored triathletes.
Sram's BB30 has a 145mm q-factor - which isn't narrower than most but is narrower than their 150mm GXP style cranks.

As a lot of people here have said, it's personal. I rode a 130mm setup on my tri bike for a while and liked it quite a bit but it isn't that much different than 145 on my road bike.
My S-works has the specialized cranks on there and it is a heck of a lot wider than 138.5mm. Also, Sram claims their BB30 cranks to be that narrow.... all of them that I have seen are just as wide as the GXP versions.
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Old 08-17-10, 01:43 PM
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BB30 won't supply a meaningfully narrower Q-factor until you put it into a frame that's specially designed to provide for it, with a wheel dished to position the cassette more inboard, and with a crank designed to compliment the special frame and wheel. Crank clearance (with the chain stays) and chainline geometry prevent it. At any rate, as has been said, it's hard to determine whether there is any real benefit to a narrow Q-factor -- or whether, indeed, a narrow Q-factor is actually detrimental.

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Old 08-17-10, 01:51 PM
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Originally Posted by briscoelab View Post
Q-factor is a very personal thing and is best assessed during a professional fit.
This. I think people make a big deal about narrower q-factor cranks because it is easier to make narrow cranks wider by moving the pedals out, but you can't really make wider cranks narrower.
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Old 08-17-10, 02:17 PM
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This is a lot of good info, and I guess what I'm finding here is that it is dependent on the rider's anatomy. And I'm sensing that most riders' ideal q-factors are pretty well accommodated by the BB/crankset combinations already out there. It was just something I was curious about.
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Old 08-17-10, 02:21 PM
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Originally Posted by merlinextraligh View Post
It's the sh*t that kills.
Now all I need is a bigger motor.
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Old 08-17-10, 02:37 PM
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I always figured the selling point for a smaller q-factor was that the system would be more stiff.
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Old 08-17-10, 03:46 PM
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wings

Originally Posted by ElJamoquio View Post
Now all I need is a bigger motor.
this should make you fly...

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Old 08-17-10, 04:15 PM
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I figure the ideal q-factor depends on your hip width and maybe even other anatomical factors.
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Old 08-17-10, 04:34 PM
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Originally Posted by krazygl00 View Post
*Note I am not trying to invent a magical drivetrain.
I really think you should reconsider.
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Old 08-17-10, 05:26 PM
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I have increased my Q using longer pedal spindles as after 2 years off the bike with chronic knee pain I found that additional Q is the solution. I have proven it many times just to be sure by fitting standard spindles back on the bike. with standard spindles I can ride about 5km before serious pain and about 10 km before I cant turn the padals at all. It will be 3 days before I can walk pain free again.

With half inch longer spindles I can ride 160km with absiolutely no pain at all. I have tested these set ups a total of 3 times over 2 years.

reduced Q is not an upgrade, it either fits you or it doesn't. People have different width hips and different knees, the bike needs to fit. Some people will benefit from reduced Q the way I have from increased Q, others (me) will find it utterly un-rideable
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Old 04-18-14, 11:56 AM
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wider q-factor reduces knee pain

Originally Posted by lazerzxr View Post
I have increased my Q using longer pedal spindles as after 2 years off the bike with chronic knee pain I found that additional Q is the solution.
I seem to have the same issue. My road bike has a q-factor of about 150mm. Both my MTB' s and my tandem have q-factors of 160-165mm. In the last 6 months, when riding the road bike, I've been getting bad pain in my right knee at the point/burser at which my bicep femoris meets the fibula head. I don't when riding the other bikes. Not sure what changed in the last 6 months though since I rode with 150mm q-factor fine before that.
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Old 04-18-14, 12:03 PM
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Originally Posted by Bob Dopolina View Post
I've thought about this before.

Who decided that a narrower Q-Factor was better? I've never seen any power data to back this up (and would like to see some) yet there seems to be a constant drive towards narrower and narrower spec.

Frankly, I have my cleats adjusted to give me a slightly wider Q-Factor because it feels far more comfortable and I certainly don't have birthing hips.
There is evidence that narrower q-factors increase efficiency The effect of Q Factor on gross mechanical efficiency and muscular activation in cycling - Disley - 2012 - Scandinavian Journal of Medicine & Science in Sports - Wiley Online Library
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Old 04-18-14, 03:15 PM
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The ideal Q-Factor is probably very closely related to your natural running gait. It will probably be slightly wider since cycling involves much more knee action than walking/running.
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Old 04-18-14, 04:20 PM
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Thanks for the link. Were off camping for the weekend so I'll have to wait until Monday to read it.
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