Q for fixers
by Will Meister
Q--or quack-factor, to give it the full name coined by Tom Ritchey--describes the distance between the outer surfaces of the left and right cranks on a given bike/crankset combination. Many experts think it's something to which we should pay more attention. In this essay, I will explain why I think that's particularly true for fixers.
First, let's deal with the impact of Q on all riders. Feeling relaxed? Good. Get up from your computer and walk a few steps. Stop. Turn. Bring both sets of toes up to an imaginary starting line.
Now, move your feet 2cm (1") further apart than they are already. Keeping your legs slightly splayed, walk back to the computer.
Welcome back. How was it? Chances are that the tiny change made a big difference. You may have found yourself waddling like a toddler. The shorter your legs, the more the impact. Small women will have felt it worst of all. Riding a bike is not the same as walking, but there are enough similarities between the two activities to suggest that low Q might be a good thing for your legs.
Second, let's consider the impact of Q on fixed gear riders. For this, you need a bike.
Bring the cranks to 6o'clock/12o'clock, and kneel on the 6o'clock side. Grab the handlebars and seatpost, and lean the bike until the pedal grounds.
Now, imagine reducing the Q factor by a centimetre or two. How much more clearance would you get? Chances are, you would be able to lean the bike another 10 degrees or so while pedalling through a turn. Useful? It might also come in handy for riding a tight wheelrut.
There's a last point. It seems to me that, when you're standing on the pedals to grind up a hill, it's a neat idea to have your feet close to the centreline of the bike. Otherwise you're using more energy than necessary just moving your weight around. Can't prove it, though.
So, reduced Q is a good thing for all riders, but especially for fixers. It makes pedalling easier, it reduces the likelihood of pedal strike, and it may make climbing easier.
Now, given these considerations, you might expect low Q to be a priority for component designers. The reverse is true. Q is on the increase.
The urge to cram in more gears has been the main driver here. In living memory, dropout spacings have increased from the 110mm of an old track racer to the 135mm of a modern MTB. BB spacings have gone with them, and, as a result, Q has too. (Woo!)
There's also the trend towards light alloy cranksets. This has often been accommodated by thickening the crank at the bottom bracket. If you get a chance, take a look at an old high-quality bike with cottered steel cranks. You may be surprised at how slim the cranks are.
Put the wider dropouts and thicker cranks together with triple chainrings, and you have a big change for your feet to accommodate. Everybody's body is different of course, but the official 63xc.com line is that less Q is a good thing.
Q is one more reason to get a retro frame. An old touring or MTB frame with horizontal dropouts is also likely to have a narrower spacing.
You might do well to consider a low Q factor crank. This doesn't necessarily mean that you should bag a classic Specialites TA track racing crankset--it may not have the characteristics you favour for grinding up a 1 in 5 quagmire. But Q is something to bear in mind when building your transmission.
Notice (again) how your choice of components diminishes when you step outside of market orthodoxies. Goldtec and Royce build rugged fixed rear hubs in 120mm spacing, as well as 130 and 135. The offerings from Phil Wood and Van Dessel are 135mm only.