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I was checking the specs of my crankset (Deore FC-M610) on Shimano's website and I saw that its q-factor was 176mm. I suppose this is the distance between your two feet when you are standing or sitting in a relaxed position. If so, my q-factor is 160mm. Do I need a narrower q-factor crankset in this case? Also how do I measure this distance on the bike?

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How to determine an optimal Q for yourself is a religious question, as is what to do with the information once you feel you have it. Generally speaking your options are limited at this point unless you're willing to look at older drivetrain types and/or spend a lot. Standard/common Q numbers have been pushed relentlessly out in the name of getting clearance to do all the other things manufacturers have wanted to do with their drivetrains. Most people are oblivious to Q and it is now comically large in many applications, especially ones where short or more lightly built humans are involved.

The numbers you cite are the distances between the two pedal mounting surfaces. Q is also sometimes expressed as a measurement of the distance between the pedal mounting face on the crank and the frame centerline, though doing it that way is a little more vague because it makes the assumption that the crank/BB configuration is giving symmetrical Q, which isn't always true. A good practical way of taking it from an existing bike is remove the pedals and use the depth gauge on your vernier caliper to measure between each pedal mounting face and the rear rim surface. To get the number as Shimano is expressing it, you're adding those two numbers together plus the outer width of the rim. To get it the other way (or in other words to measure one side's Q), you're taking each number and adding half the rim width.

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    Interesting, one answer calls it "comically large", the other "if anything, some riders should increase their total stance width (Q-factor plus pedal spindle length), and some more could benefit from doing so". Apr 18 at 15:37
  • @VladimirFГероямслава One's stance widens with age, so entirely plausible riders could beneft as they age.
    – Criggie
    Apr 18 at 19:14
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Technically, q-factor is the horizontal distance between the outer faces of each crankarm. The q-factor has nothing to do with your stance width while at rest. I am not sure how convenient it is to actually measure. That said, we just take the manufacturer’s specs at face value.

I sometimes listen to podcasts or YouTube videos by bike fitters. I think that, if anything, some riders should increase their total stance width (Q-factor plus pedal spindle length), and some more could benefit from doing so. I’m not sure how the standard road Q-factor of about 145mm evolved, but the majority of us seem to be able to adapt to it. The body can, after all, adapt unless things are much too big or small or whatever.

With MTBs, the Q-factors are a lot wider. 172mm sounds like MTB width. If this is an MTB, it is physically not possible for you to fit a crank with a 160mm Q as it would hit the chainstays. What if you find MTB cranks unworkably wide? I seriously don’t know, but there are hard physical constraints if you want to have that tire width.

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    Paul is correct. "Adapted" means that the Qs are in the range of Q factors that most people can work with, and our bodies adjusted accordingly.
    – Weiwen Ng
    Apr 17 at 20:14
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    Just wanted to confirm: inner faces of the crank arms or outer faces? Every internet source I saw in my 30 second search said outer, and that's what I remember it being as well.
    – MaplePanda
    Apr 17 at 21:46
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    It is outer, I had been meaning to correct that.
    – Weiwen Ng
    Apr 18 at 0:58
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    “The q-factor has nothing to do with your stance width while at rest” There is a common recommendation on the Internet that when you walk around and stop the stance width you (unconsciously) end up with is the one you should choose for your Q-factor on the bike. I somewhat doubt this recommendation, for me it would mean I need a 10cm Q factor.
    – Michael
    Apr 18 at 8:59
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    @Michael Exactly. Also, you barely even have a choice of Q. Shimano, SRAM, and Campy have Qs within a few mm. A number of 3rd party cranks do have somewhat wider Q. But very few options. Zero of them for narrower Q.
    – Weiwen Ng
    Apr 18 at 10:59

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