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Old 11-14-17, 05:04 PM   #1
mtb_addict
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Offset Q factor

I don't know the proper tech term...but I measured the distance from pedals to the center-line of the bike.
The left pedal is 5mm more than the right pedal.
That would explain why my left knee seems further away from the top tube than my right while pedalling. I have been trying to shift my hip to correct this aissematry, cuz I thought my left leg might be longer than my right. Finally measured it...and confirmed: it's not my leg...it's the pedal offset.

I measured another bike...same 5mm difference...interesting...I'm seeing a trend here.

Why does they make them that way? Why not make both sides the same?

Last edited by mtb_addict; 11-14-17 at 05:09 PM.
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Old 11-14-17, 07:00 PM   #2
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Are you possibly missing any of those 2.5 mm spacers that often go on the right-hand side of the bottom bracket?
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Old 11-15-17, 08:41 AM   #3
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Both sides should be the same, unless your bike fitter tells you otherwise. You'll need to add a 2.5mm spacer under the right side bottom bracket cup or on the spindle. There's a chance that you'll find an extra 2.5mm spacer on the left side to use.

Do you have MTB cranks on a road frame?

Why? Typically MTB bottom bracket shells are 5mm wider than road ones (which keeps the chainline happy with the 5mm wider rear hubs on MTBs vs road bikes). Many standard bottom brackets will fit both bottom bracket shell widths, under the assumption that road bikes will have road cranks installed and MTBs will have MTB cranks installed. When you mix and match, spacers are often needed to sort out the difference.
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Old 11-15-17, 09:09 AM   #4
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Interesting...
I measured the aisymetry in my Dahon Boardwalk folding bike and my Shogun 21-speed MTB. Dahon has a cartridge square taper BB. Shogun has those cup-n-cone style BB.

I measured my Windsor Wellington road bike. And it is perfectly symetric.
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Old 11-15-17, 10:26 AM   #5
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You’re overthinking things again.
Any important differences in how close your knees pass the top tube are far more likely to come from body assymmetry than from bicycle assymmetry.

Unless it’s hurting, don’t fight it. Let your body find its own way.
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