# Crankset Question: Q Factor and Chainline



## Rhino4Five (Nov 5, 2009)

I currently have a triple setup, and I'd like to change to a double.

Triple Stuff:
Crankset: FSA Gossomer Mega-Exo 2 Piece 
BB: FSA Mega-Exo Integrated External Cartridge Bearings

Double Stuff:
Crankset: FSA SL-K Light Carbon 53/39
BB: 66 mm
Chainline: 43.5 mm
Q Factor: 147 mm


I don't know what my current Q Factor and chainline are. Can anyone shed some light on how to figure this out? And what exactly is the chainline measuring?

Anything else I need to consider regarding the cranks before making this swap? I'd like to keep the fit identical.

Thanks!


----------



## SilverStar (Jan 21, 2008)

Q factor is the measurement of "tread" -- the distance from the outer side of the crankarm at the pedal hole to the outer side of the other crankarm at the pedal hole:

http://www.sheldonbrown.com/gloss_q.html#qfactor

Front chainline is the measurement from the centerline of the seat tube to the middle of the space between the two chainrings in a double-ring crankset. It's usually between 40 mm and 45 mm, give or take.

As long as you use the proper BB for each crankset, you should have no problems with chainline. As for Q factor, some people are sensitive to gross changes in that "tread", while many others are not.


----------



## Rhino4Five (Nov 5, 2009)

SilverStar said:


> Q factor is the measurement of "tread" -- the distance from the outer side of the crankarm at the pedal hole to the outer side of the other crankarm at the pedal hole:
> 
> http://www.sheldonbrown.com/gloss_q.html#qfactor
> 
> ...


Thank you, that was very informative. Are there standard Q factors lengths for BBs? If I measure the Q factor myself, I am likely to be off a couple of millimeters. Is the Q factor written anywhere? I can't seem to find any information from the manufacturer.


----------



## wim (Feb 28, 2005)

*Some information.*



Rhino4Five said:


> Thank you, that was very informative. Are there standard Q factors lengths for BBs? If I measure the Q factor myself, I am likely to be off a couple of millimeters. Is the Q factor written anywhere? I can't seem to find any information from the manufacturer.


The Q-factor is the dimension pedal eye-to-pedal eye on the outside of the cranks _with the cranks installed as recommended by the crank manufacturer_ on a standard bicycle frame. Almost always, the Q-factor of a double is less than that of a triple. But numbers are hard to come by—most manufacturers don't deem it to be a terribly important piece of information.


----------



## Rhino4Five (Nov 5, 2009)

Thank you for the responses. I understand the issues much better now.

The double crankset has a Q Factor of 147 mm, while my current triple has a Q Factor of 159 mm. Am I likely to notice a 12 mm difference? 

Worse case that I do, what can I do after the fact to mitigate this? Move cleat position? New BB?


----------



## Marc (Jan 23, 2005)

Rhino4Five said:


> Thank you for the responses. I understand the issues much better now.
> 
> The double crankset has a Q Factor of 147 mm, while my current triple has a Q Factor of 159 mm. Am I likely to notice a 12 mm difference?
> 
> Worse case that I do, what can I do after the fact to mitigate this? Move cleat position? New BB?


You're talking 1/2" thereabouts in difference totaled, divided between both feet. So 1/4" on each foot.

You can move your cleats...or if you have pedals that allow Q adjustment. Lots of ways of skinning a cat.


----------



## wim (Feb 28, 2005)

Rhino4Five said:


> Worse case that I do, what can I do after the fact to mitigate this? Move cleat position? New BB?


Just curious—why do you think you have to "mitigate" the difference in Q-factor? But as said, just shove the cleat on your shoe as far as you can towards the inside of each foot. New BB doesn't work—the set-length spindle on a 2-piece crank is part of the crank, not the BB.


----------



## Rhino4Five (Nov 5, 2009)

wim said:


> Just curious—why do you think you have to "mitigate" the difference in Q-factor? But as said, just shove the cleat on your shoe as far as you can towards the inside of each foot. New BB doesn't work—the set-length spindle on a 2-piece crank is part of the crank, not the BB.


In the worst case that the difference in Q Factor (going from triple to double) causes some fit issues, I was wondering if there were simple ways to lessen the impact of the Q Factor difference.

I suspect that it will not be an issue, but on the off chance it is, I want to know there is an affordable solution. I know a cm isn't much, but I've heard of bad things happening after making very minor tweaks.

Haha, thanks for shedding light on my dumb BB question. That makes complete sense after reading it aloud (albeit, in my head).

Everything I am reading seems to imply that the average rider prefers the narrower Q Factor. Hopefully this is also the case with me.

Thanks!


----------



## wim (Feb 28, 2005)

*Overthinking Q.*



Rhino4Five said:


> Everything I am reading seems to imply that the average rider prefers the narrower Q Factor. Hopefully this is also the case with me.


Correct, a lot of riders would rather have a narrow Q-factor than a wider one. Some even base their choice of crank on that—if it's not narrow enough, it doesn't get bought.

But realistically, most riders (myself included) don't really care one way or the other. If there is a difference in Q-factor, you feel that difference the first few hours of riding only. Then the resiliency of the human body will take care of that change and you'll never give it another thought. There are fit considerations where one centimeter or less _does_ make a difference (like saddle height), but you can't apply that to everything on the bike. Before the "Q-factor" was "discovered" by someone in the 1970s, people never even thought about how far their feet were apart on the pedals—and won races, including Tour de Frances, anyway.


----------



## Rhino4Five (Nov 5, 2009)

wim said:


> There are fit considerations where one centimeter or less _does_ make a difference (like saddle height), but you can't apply that to everything on the bike.


Thanks for all the good information, Wim.

My concern w/the 1 cm Q Factor is exactly for the reason you mentioned above. A few weeks ago, I raised my seat about 1 cm just before a big ride because I was having some calf discomfort (raising the seat in the past helped). But it must have been too much b/c I started having some knee pain. I lowered the seat after the ride, but I still have some knee discomfort after hard efforts. 

I was particularly concerned w/the Q Factor because I didn't want to revisit these knee problems.

Thanks again! I won't worry about it unless it becomes an issue.


----------



## cyclequip (Oct 20, 2004)

Rhino4Five said:


> Thanks for all the good information, Wim.
> 
> My concern w/the 1 cm Q Factor is exactly for the reason you mentioned above. A few weeks ago, I raised my seat about 1 cm just before a big ride because I was having some calf discomfort (raising the seat in the past helped). But it must have been too much b/c I started having some knee pain. I lowered the seat after the ride, but I still have some knee discomfort after hard efforts.
> 
> ...


Going with the narrower stance width on the double crakks will elevate the potential for ITB issues, especially if you have experienced knee pain in this area. Your post doesn't indicate this. 
If ITB does rear it's head, go with the cleat move - get the cleats as far to the inside of your shoes as you can.


----------



## andulong (Nov 23, 2006)

Rhino4Five said:


> Anything else I need to consider regarding the cranks before making this swap? I'd like to keep the fit identical.
> 
> Thanks!


If you want to keep the same...buy the same length crankarms too. Should be stamped on the back somewhere.


----------



## kiwisimon (Oct 30, 2002)

Watch that your new setup will clear the chainstays.


----------



## utracer (May 1, 2008)

I know this is an old thread, but I have searched and searched and cannot find a definitive answer. I recently changed bikes from a frame with GXP SRAM Red to a Cannondale with a PF-30 and Hollowgram Crank. Most all parts swapped, I setup the geometry to be almost the same. The only thing that I can tell is really different is the Q-Factor (Stance). The hollowgrams feel a lot narrower, and I can feel a tiny bit of pressure on the outside of my knees. After long rides both my knees start to hurt. As a temporary solution I put a couple pedal washers on each side, and this helped, but the pressure and eventual knee pain persists.

I measured the Q-Factor of my Hollogram Cranks and they measure 144mm. Does anyone have or know of a definitive list of actual measured Q-Factors? I am most interested in what my old Crank was, and more than anything just like to know what the new 2012 SRAM Red measurement is? I do not believe the SRAM documents, they often have a lot of "cut/paste" errors between their models and BB Interface types, I just don't trust what is on their website or in their tech docs. 

Any information would be greatly appreciated. Thanks.


----------



## Agent319 (Jul 12, 2012)

I have a Klein Performance with Dura-Ace AX with triple rings. Can I move to a dual ring crank?


----------



## AndrwSwitch (May 28, 2009)

Yes.

Consider a double front derailleur when you make the switch. Just use the limit screws on it to lock out the highest-tension setting in your shifter.


----------

