I’m looking at a set of cranks for my daughter, and the Q-factor is 160mm. I believe the typical Dura-Ace/Ultegra Q-factor is 145 (?)
She’s very petite and I’m wondering if the wider Q-factor will in some way be more detrimental to her because she’s smaller (narrower hips, etc.).
In that regard, in what way does Q-factor affect someone?
Is 160mm wide?
I read somewhere that having a wide bottom-bracket can create drag. Supposedly the extra width resulted in similar numbers to riding on the tops as opposed to riding on the drops. They didn’t seem to consider aerobars. It makes sense to me that being narrow is just important as being low. That said, you also have to consider biomechanics and some people seem to need more Q (width). Being aero doesn’t help much if your knees are screaming. Any chance she can test ride a bike with a similar bottom bracket?
The difference is the width of your finger; we have that much variance simply from one step to the next when running or walking. Q-factor is only a problem if it is … a problem. And, it’s a complete non-issue for 99.99% of bike riders. People with abnormalities or injuries sometimes need to seek a specific Q-factor (narrower or wider). This can usually be accomplished simply by shifting the cleats around on the shoe bottom.
Marketing hype aside, just ride the bike and forget all that nonsense.
I think Q-factor isn’t a big issue for most people, but if you have biomechanical constraints it can have a huge effect. The addition of about 1 mm worth of shims between my cranks and my pedals helped my IT band and lower back problems on the bike immensely. Andy Pruitt (Boulder Center for Sports Medicine) covers Q factor and shimming out your pedals in his book on bicycle fit.
Once again, I think the majority of people don’t worry about Q-factor at all (other than that having your knees close to the bike is supposed to be more aerodynamic), but if you’re having biomechanical and injury issues, playing around with it can help alleviate things a bit.
J
How important is Q-factor? It is as important as any other fit tool or opportunity, that is: Pretty important.
When you start talking about $1000+ bikes one of the things a customer is paying for is a substantial degree of “tunability” with regard to fit. I think every resource should be employed to the fullest to maximize fit.
Q factor is an opportunity to dial a person’s hip width to their foot width or stance on the bike. That is a good opportunity and not to squandered. Cranks and BB’s aren;t the only place to exert an influence on “Q” factor though. Cleat adjustment facilitates that also.
“Q factor is an opportunity to dial a person’s hip width to their foot width or stance on the bike. That is a good opportunity and not to squandered. Cranks and BB’s aren;t the only place to exert an influence on “Q” factor though. Cleat adjustment facilitates that also.”
Tom, it’s interesting that you mention this. I asked a similar question about optimal Q-factor varying from person to person when the big debate about the compact double vs triple was raging. My premise was that if handlebar width varies based on shoulder width, why wouldn’t q-factor vary by hip width. Gerard (I believe) had responded and indicated that no study had ever indicated that varying Q-factor made any difference in power, and that, in fact, people have a negative Q (overlap of feet) when they run so this would seem to indicate that the most narrow Q possible should be the most efficient. There were no other takers on my question at that time. I still wonder whether Q should be related to hip width, and it seems that this is what you’re stating? If so, what would be the fitting parameters or formula for this?
Hmmm, well, my perspective on Q factor as a fit tool is not so much a performance enhancing opportunity (although that capability may exist) as it is an injury prevention initiative.
Here’s an example, and this is a pretty common one:
Customer comes into the store with medial knee tightness or pain. It is springtime and they have been riding outside under 70 degrees fahrenheit without their knees covered and they have done substantially more mileage in the previous 2 weeks than they have per week in the previous 3 months. They are a recipe for knee discomfort.
As viewed from the front the customer’s knees are symmetrical in their proximity to the top tube during
pedalling. However, if you visualize an imaginary vertical line from (about) where the customer’s femur intersects their pelvis downward to the floor, perpendicular to the floor, you suddenly notice the angle of their femur and tibia is splayed outward (laterally) from this. In other words: Their feet are a lot wider apart than their hips. As you watch them pedal you realize their are only three places this lateral angulation away from the hips can be facilitated:
So, understanding this and still viewing the cyclist from the front as they pedal, where is most oof the outward angulation in their legs taking place? Well, normally, it is where the femur comes out of the pelvis. Not a huge problem as the joint is made to faciliatate some degree of movement in that range of motion (since it is a ball joint).
However, you get to the knee, and you have the medial and lateral collateral ligaments (as well as some involvement of the anterior and posterior crutiate ligaments) trying to hold the knee in relatively rigid lateral station. Now, with this outward angulation of the leg proper (as a whole), there is some opportunity for asymetrical loading of the medial side of the knee, contingent upon the person’s pedalling style. Big gears can cause big problems here.
So…
It is common sense: Shove the person’s feet under there hips by:
I hope you can follow all that. It is not rocket science, just good old mechanical sense. I am not surprised there isn’t a study that quantifies the value of Q factor. it doesn’t necessarily mean it is not there, or that it is.
I can tell you anecdotally that we have had a number, quite a large number in fact over the years, of customers who have had knee distress that has been moderated or eliminated by managing their Q facotr among other variables.
Good comment and question. Thank you.
Thanks Tom. Great explanation (as usual). This, of course, brings another question to mind… if q-factor is indeed a fit parameter, why doesn’t Shimano or Campy make a range of cranks with varying q-factor just as they offer varying crank arm lengths? Is the range of practical q-factor positions easily accomodated with cleat positioning alone? It would seem to me that a 1-2mm change in q-factor would be significant, whereas (as argued elsewhere) a 2.5mm change in crankarm length may be of no practical value at all, yet I can buy the latter. Is this simply a situation where the common belief is that the most narrow Q is the best, so no one would buy a wider q crank even if it was offered and it fit them better? I would have to believe that if Shimano or Campy came out with a range of cranks with varying q-factor people would stop and say “hey, maybe I’ve been missing a key element of my fit.”
As I can see it, (depending on the bike) one limit to narrowing Q-factor is chainstays. Spin your cranks around backwards and see how close they come to the chainstays. Most of my bikes have a good amount of room, but two of them come within 7-8mm of the chainstays.
A thought… instead of varying the q-factor on the cranks, can’t you achieve the same thing by changing the spindle length?
As I can see it, (depending on the bike) one limit to narrowing Q-factor is chainstays.
Not only the chainstay, but also the size of your feet, I have to move my shoes to the outside of my pedals to allow my heel at the rear most position to clear the chainstay. A narrower Q for me would be of no benefit at all
Norty
I think it boils down to cost. Heck, it is difficult to get consumers to acknowledge the differences between cranks lengths, let alone (if) Q factors were optional. Also, it would increase the numer of SKU’s at the distributor/manufacturer by an enormous margin. I don’t think Shimano or Campagnolo sees enough appeal at the consumer level for this kind of flexibility. That said, Look has done a good job of addressing it with some of their pedals that do have a quasi-Q-factor adjustment capability that is reasonably effective.
Yesterday I bought a new 2004 Campagnolo Record kit for a bike. I had to make a lot of phone calls and call in some favors to get a 2004 Carbon Record crank, and I couldn’t get the size I really needed, I had to compormise and get 172.5 with the understanding I can swap it out for 175mm when they are available. This stuff is hard enough to find as it is. Adding more options would make it even more difficult.