By Matt Lamy
Before going any further we should define what is meant by ‘Q Factor’. Q Factor is the distance between the outside of one crank arm to the outside of the opposite crank arm. Although Q Factor has become a universally recognised measurement, other people in the bike trade prefer to use a value for ‘stance width’ — which refers more directly to the distance between feet on the pedals.
Both terms are part of the same notion regarding the width of the crankset assembly and, stemming from that, the lateral distance between feet when pedalling. But how does it effect cycling?
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“You really get a sense of the importance of Q Factor if you ride a fat bike,” says Specialized’s David Alexander. “In order to get the chain past those fat tyres, the cassette needs to be pushed out further. The bottom bracket therefore has to go über wide, and the bottom bracket is massive on most fat bikes. So when you get on a fat bike you feel like you’re trying to pedal the sides of a horse. It is an odd experience.
“At the other end, going too narrow with your Q-Factor in the search for speed has problems, too. When Lance Armstrong tried to copy Jan Ullrich’s Walser time trial bike with an ultra-narrow machine, the results weren’t all positive. Although that produced some increased power to begin with and was initially fast, the speed rapidly and dramatically dropped away on an average length time trial of between 28 and 40 kilometres,” Alexander recalls.
“It was initially faster but there was no sustainability. So a narrow Q Factor doesn’t necessarily afford every rider with a sustainable performance benefit. It might give you something to begin with because you think you’re being more aero, but it doesn’t work for everyone.”
Q Factor has to take into account more than just biomechanics — there are limitations due to bottom bracket size, chainstay length and minimum chain line guidelines from people like Shimano, SRAM and Campagnolo. Manufacturers are limited to how short chainstays can be and how far out they can go with cogs at the back, while still maintaining a traditional 68mm shell bottom bracket.
“I’ve heard people really get bent out of shape by Q Factor and the Q Angle of the knee and how it affects riders,” says BMC’s Thomas McDaniel. “Q Factor is a fixed position in space and it’s something that we can all appreciate because it is a set idea. But ultimately pedals and pedal spindle length and cleat choices and how you mount them to the shoes are really how you affect the overall stance width.
“As a manufacturer at BMC — because we rely on other manufacturers to make our cranks — we are at the mercy of their production standardisation to have a certain value for Q Factor."
Some companies, such as Cannondale or Specialized, make their own cranks, and can alter their own Q Factor if they want to, but both those companies’ bikes still tend to fall within the industry norm. Very roughly speaking, Q Factor tends to be about 150mm for a road bike and 170mm for a mountain bike.
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“I think within the boundaries of reasonable bike-fit expectations, most people are pretty comfortable with those existing Q Factor figures. Because cycling can be such a static position I think manufacturers and riders and bike fitters are all coming to the consensus that the more narrow standard for road application makes a lot of sense. You can always go wider, whether with a longer pedal spindle or sliding your cleats, but you can’t go narrower.”
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Q Factor is largely beholden to engineering constraints that are beyond the rider’s control, but stance width can be manipulated. If you feel your feet aren’t in the right place when pedalling, a good bike fitter should be able to make some adjustments that will make you more comfortable. It’s better to be a happy rider than chase after a theoretical performance gain.
Does Q Factor make a difference?
Yes: David ‘DA’ Alexander, Specialized Bicycle Components, University and BodyGeometry FIT expert
“Stance width is hugely important from a biomechanical standpoint. As manufacturers, Q Factor plays a massive role in how we try to maintain our chain line so that it’ll work with really short chainstays or something designed for a more stable ride, with longer chainstays. If you want your chainstays super-short, sometimes you have to space things differently at the rear or you can increase your Q Factor at the front.”
No: Thomas McDaniel, BMC product marketing manager, MS Biomechanics
“We have to work within the constraints of manufacturers’ products, so Shimano, SRAM, Campagnolo dictate to us what our bottom bracket standards are or what they can be, and from that derives Q Factor. Even when companies alter chain line they tend not to affect Q Factor very much, and most riders find that existing Q Factor figures are not a problem. Stance width can be manipulated by a bike fitter or rider via pedal choice or cleat placement.”
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