You will be hearing more about "Q Factor" from Spinning® / Star Trac so I thought you may appreciate knowing what it is, in case it comes up in conversation.

Q Factor (also know as Tread) is simply the separation/distance between the two pedal cranks of a bicycle or Indoor Cycle. Here are two articles here and here that discuss this measurement and this picture illustrates how it is measured.

Q factor on a spinning indoor cycling bike

What prompted this post was a conversation I had last week with Josh Taylor from Spinning® about the changes to the latest version of the Spinner® NXT and the new Spinner® Blade. Josh explained to me that one of their design criteria for both cycles was to reduce the Q factor, without reducing the reliability of the Bottom Bracket Wikipedia article. The purpose of the change was to make the new Spinners more Bio-Mechanically efficient. You've no doubt heard about "knee over pedal" that can be adjusted by seat position and shoe cleat alignment. Alignment between Hip Joint > Knee > Feet is also important. For some people bringing your feet closer to their natural spacing will maximize the muscular forces applied to the pedals. Notice I didn't say all people. According to the company who manufactures the KneeSaver there are people (specifically those with wider hips) who benefit from a wider Q-Factor.

You can read more from Josh at his own blog and it includes his descriptions of the new Spinner® NXT and Blade.

I wanted to get a point of comparison so I pulled out my trusty vernier caliper and measured a few Indoor Cycles + two of my road bikes to see how they compared:

  • Amy's Trek Women Specific Road bike = 156mm
  • Our Trek Tandem Road bike = 165mm
  • Spinner® NXT = 170mm
  • Schwinn AC Performance = 170mm
  • Keiser M3 = 197mm
  • New Spinner NXT and Blade will be 158mm per Josh Taylor, which is very narrow.

There are a number of design factors that determine Q Factor on an Indoor Cycling bike:

  • Interference from the frame, guarding or other component requires the pedal crank arms be spaced further apart. This is especially obvious on the Keiser M3 and what causes their 197mm Q Factor. The carrier assemble for the Magnetic Resistance on the M3 sticks out on the RH side requiring a special pedal crank assembly.
  • Are the pedal cranks off the shelf, or custom made?
  • The width of the Bottom Bracket used.

Josh explained to me that once they set a target Q Factor for the new Spinners they realized that they would need to focus their engineering creativity on reducing the width of the Bottom Bracket. Not an easy task. The Bottom Bracket is the most highly stressed part on any pedal driven machine. Think about all the forces that need applied here; the rider's body weight + the twisting force (torque) that's applied to a machine that doesn't move. The Bottom Bracket is made up of an axle that's supported by two roller bearings, one one each end. How far the bearings are apart effects the amount force applied. The wider you space the bearings (and the frame that supports them) = better, which is OK unless you are trying to reduce the Bottom Bracket's width.

Star Trac's solution to this problem was to design a narrow Bottom Bracket with larger bearings and strengthening the frame that supports these bearings. To ensure the crank arms stay securely attached they are using a Morris Taper, instead of the typical interference fit and bolt used in the past. Based on the dimensions Josh is reporting they now have the Indoor Cycles with the narrowest Q Factor on the market.

Why should you care?

I know from experience that the narrower the Q Factor, the closer my feet are to each other, the more comfortable I feel riding a bicycle. This is especially true on a long ride and some cyclists will go to great lengths to reduce their total Q Factor by adjusting shoe cleat position, effectively moving their feet as close together as possible.

But we aren't talking about your personal bicycle here, where changes and adjustments can be made to fine tune the fit of the owner. These are Indoor Cycles. They're designed to ridden by every conceivable variation of human adult; short, tall, wide hips, narrow hips, leg length disparities, etc...  Will some in your class notice or appreciate the difference? Maybe. But I personally don't see how a narrower Q-Factor will help our typical students in any measurable way.

I would love your thoughts...

Originally posted 2011-04-24 07:47:55.


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