General Cycling Discussion Have a cycling related question or comment that doesn't fit in one of the other specialty forums? Drop on in and post in here! When possible, please select the forum above that most fits your post!

Offset Q factor

Reply

Old 11-14-17, 05:04 PM
  #1  
mtb_addict
Senior Member
Thread Starter
 
mtb_addict's Avatar
 
Join Date: Jun 2011
Posts: 2,325
Mentioned: 13 Post(s)
Tagged: 0 Thread(s)
Quoted: 1557 Post(s)
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.
mtb_addict is offline  
Reply With Quote
Old 11-14-17, 07:00 PM
  #2  
JonathanGennick 
Senior Member
 
JonathanGennick's Avatar
 
Join Date: Apr 2007
Location: Munising, Michigan, USA
Posts: 3,462

Bikes: Priority 600, Priority Continuum, Devinci Dexter

Mentioned: 7 Post(s)
Tagged: 0 Thread(s)
Quoted: 355 Post(s)
Are you possibly missing any of those 2.5 mm spacers that often go on the right-hand side of the bottom bracket?
JonathanGennick is offline  
Reply With Quote
Old 11-15-17, 08:41 AM
  #3  
OneIsAllYouNeed
Long-term wear tester
 
Join Date: Dec 2006
Location: Seacoast, NH
Posts: 559

Bikes: Granite Tandem Design travel/gravel/family tandem, KHS CX200 road/gravel, Voodoo Agwe fixie commuter, Gunnar Sport road, Trek T200 tandem, Motobecane Boris fatbike

Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 163 Post(s)
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.
OneIsAllYouNeed is offline  
Reply With Quote
Old 11-15-17, 09:09 AM
  #4  
mtb_addict
Senior Member
Thread Starter
 
mtb_addict's Avatar
 
Join Date: Jun 2011
Posts: 2,325
Mentioned: 13 Post(s)
Tagged: 0 Thread(s)
Quoted: 1557 Post(s)
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.
mtb_addict is offline  
Reply With Quote
Old 11-15-17, 10:26 AM
  #5  
dabac
Senior Member
 
Join Date: Mar 2008
Posts: 7,565
Mentioned: 30 Post(s)
Tagged: 0 Thread(s)
Quoted: 701 Post(s)
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.
dabac is offline  
Reply With Quote

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Thread Tools
Search this Thread

Contact Us Archive Advertising Cookie Policy Terms of Service