What is "Q" and what purpose does it serve

Just like the title says Waht exactly is Q and what purpose does it serve

Q factor is on some splined cranks, it is when the cranks are sticking more out… << donno if u understand this.

The actual, correct answer is that Q factor is a measure of the distance between the pedals. A wider hub will tend to have a higher Q-factor. Some cranks angle outwards, which also increases Q-factor.

Most people prefer lower Q-factor (pedals closer together), but others like their legs more splayed out. In practice, it generally doesn’t matter much.

That I understand, but is there any specific benefit or disadvantage to having Q
Is there any difference in torque applied in downward motion due to Q vs zero Q

You always “have Q.” The benefit to having Q is that otherwise there wouldn’t be room for the wheel in between your pedals.

Whether your cranks are straight or not may be better or worse, depending on the size of your feet and whether you pronate.

A wider hub will generally make for a stronger wheel.

A wheel with a high Q-factor will probably be marginally more wobbly when you’re riding it, as the force vectors aren’t as well aligned with the plane of the wheel.

What about Q on crank arms vs straight crank arms? is there any pros or cons to Q on the cranks

Im not sure but i belive that you dont hit your andkles on the nubs of your cranks(because your freet are father away) but thats all I know.


Q-factor is not a binary quantity; if you’re interested in straight vs. angled cranks, just say so. Both types contribute to Q-factor.

I think for unicycling, straight cranks are probably better. Unicycles don’t have the problem that many bikes do of needing the cranks to angle outwards to avoid hitting the chainstay. Straight cranks are probably marginally stronger, and most people will probably have fewer heel/ankle hits on straight cranks compared to angled cranks, although it depends on your particular feet.

A crank arm with Q vs a straight crank arm, it makes sense to me that a straight arm would be more efficient for torque applied vs a Q arm which is not a straight down push when pedaling or climbing a hill etc
Tom I posted this before I saw your last post

I notice a huge difference in feel and handling between my narrow hub, steel rim Coker and my ultra-wide hub, Airfoil Coker due to the weight difference of the rims and the difference in Q.

For the sake of keeping this response relevant to the question asked, I’ll try to isolate the differences based on Q alone (and eliminate the weight difference factor).

The wider hub Coker is significantly more wobbly. This characteristic initially prevented me from comfortably maintaining high speeds. Though I did learn to adjust my pedaling motion somewhat which helped reduce the amount of wobble and helped me maintain a decently fast speed… the wider hub Coker just doesn’t feel as comfortable to me for high speed riding.

The wider hub Coker is also more responsive to turn inputs (especially with a good tire pressure), which you may feel is a positive thing or a negative thing, depending upon your preferences and what you are used to.

The first time I tried one leg extended riding on my wide hub (high Q) Coker, the leg that was extended kept getting hit by the wheel on almost every revolution… which I found incredibly irritating since that had never happened to me on my narrow hub Coker. I learned to adjust my riding technique pretty quickly to solve that problem, but I thought telling you about this experience would be a good way to illustrate how Q can affect riding. Hope I’ve been helpful.

This should explain it:

An Article by Warren Beauchamp
Q&A Making it Wide Making it Narrow Examples Crank Length Conclusions
Questions and Answers
Q: What is this Q-factor thing?
A: Q-factor is a commonly used term which refers to the distance between the pedals.

Q: How do you figure out what your Q-factor is?
A: This distance can be easily measured by removing one crank arm and turning it around so both crank arms point in the same direction, and then measuring the distance between the outside of the crank arms. This measurement is normally in millimeters. A less accurate, but tool-less method to measure the Q-factor is to measure from the outside of one crank arm to the outside of the seat or boom tube, do the same for the other crank arm, and then add these measurements to the width of the seat or boom tube.

Q: Why do I care about Q-factor?
A: Usually because you are trying to minimize it in order to make the nose of a fairing smaller, sometimes to optimize it to better match it to your hip width in order to minimize a hip, knee, or ankle pain situation.

Making it Wide
It’s easy to make it wide. Just get some MTB cranks and a wide bottom bracket (BB). If that’s not wide enough you can always add pedal extenders…

Making it Narrow
Mostly what I’d like to talk about are methods of narrowing the Q-factor, because that’s what many of us need to do when building a streamliner, or when wanting to keep ourselves in a nice aerodynamic package. The two things you can change to narrow the Q-factor are the cranks and the BB. Cranks are not typically rated by Q-factor, but MTB cranks are typically about 20mm wider than road cranks. BBs commonly come in widths between 107mm and 118mm.

When thinking about using a narrower crank, think about how many chain rings you will need. If you will need a triple chain ring, you probably want to stick with an MTB crank, if you only need two, you can use a road crank, and if you only need one chain ring you can use custom narrow crank, a specialized BMX crank set like the Odyssey Black Widow Euro (See Black Widow Lites cranks on DansComp.com) or an obsolete French crank set like the B.S.A. Nervar.

If you still need to get narrower, you can use a custom BB. Phil Wood makes a 96mm BB as a stock item, which requires a narrowed BB shell, and a special Phil tool to install it.

If you still need a narrower Q-factor, you can hack a couple inches out of a perfectly good 107mm BB spindle and weld it back together, making it about 53mm. The Coslinger team used this technique on their Coslinger streamliner. Thom Ollinger says he cut about 2 inches out of the spindle. To make it work he used a hollow BB spindle, cut it, and pinned it together. He made a fixture to hold it straight and with the crank flats lined up, and then TIG welded it. He then built up the bearing areas with weld and turned them on a lathe, leaving about .020 on the diameter. After that he put the part between centers and ground the diameters to match the inside diameter of the bearings. There is only .060 between the two bearings. This allowed them to have a Q width, plus shoes width of 12 inches. While a BB narrowed in this manner is perfectly good for racing, the bearings are so close together that there will probably be a little play and reduced bearing life. Also available is a custom manufactured 61mm BB spindle and bearings from Phil Wood. Thom had Phil Wood make up a small run of these beauties.

This custom Phil Wood BB spindle and bearings require a custom BB, but allow us to have a 4.1 inch Q factor with the Shimano cranks, for a total pedal box width of 13.1 inches.

Q-Factor Examples

BB Crank Q-factor Total width with shoes
107mm Campi MTB 171mm (6.7") 15.7"
107mm Shimano 105sc
151mm (5.9") 14.9"
107mm Odyssey Black Widow Euro 130 mm (5.1") 14.1"
96mm Shimano 105sc 141mm (5.5") 14.5"
96mm Odyssey Black Widow Euro 119 mm (4.7") 13.7"
61mm Shimano 105sc 105 mm (4.1") 13.1"
61mm Odyssey Black Widow Euro 84 mm (3.3") 12.3"
53mm Odyssey Black Widow Euro 76 mm (3.0") 12.0"
53mm custom 64 mm? (2.5") 11.5"

Crank Length
Reducing crank length is also important toward making the nose area of your shell smaller. Cranks are typically 175mm. Even if you have the monster long legs, 165mm cranks are not going to hurt your power or cadence. Cranks down to 145 mm in length have been used to good effect in Streamliners by racers like Robert LaFleur in his Zebra bike . Cranks like the Odyssey Black Widow Euro are available down to 150mm in length. Cheaper MTB or BMX cranks, which are not particularly light weight or low Q can be re-bent to acheive a lower Q. Re-bending cheap cranks is the method used by the George Georgiev of the Varna team to achieve low Q. Most higher quality cranks are not re-bendable. Changing from 175mm to 145mm cranks can save you over 2.5" in nose height! Using a 165 crank, and the BB height on the 'Cuda, which is about 12" above seat height, I found a pedal box height of 23 inches (size 11 feet). Shortening the cranks to 155 saves about an inch, so that would be around 22 inches. A 145 crank gets you down to 21 inches height.

Mechanical means can also be used to reduce the pedal box size. The Kingsbury team uses a complicated crank system called the K-drive to obtain an elliptical pedal path. This is probably as close as you can come to a linear drive system without all the power loss associated with linear drive systems.

To make pedal box measurements you can get someone to watch you pedal on a trainer and do some measurements. Sean Costin made a video of himself to observe how he pedaled, which was how they optimized the Coslinger fairing to his exact pedal stroke. Alternatively you can just hang your shoes on your pedals, and start measuring. The top of the stroke is pretty easy. Almost everyone’s stroke is with the toe straight up from the pedal at the top of the stroke. The bottom of the stroke varies more by BB height and personal pedaling style. If you pull on the pedals more, your foot doesn’t hang down as far. Even though you can make your foot hang straight down at the bottom of the stroke, this never actually happens while you pedal, so make sure you measure this well, and you can potentially save a lot of pedal box height.

Summing it up
So, with off the shelf parts (96mm BB with a Shimano 105sc crank set), you can save 1.22 inches off the Q-factor of your typical recumbent crank set, and make the nose of your fairing that much narrower. With these 165mm cranks, this would give you a pedal box size of 14.5 inches wide, by 23 inches high. If you want to go completely wild, you can make the nose of your streamliner over 4 inches narrower, and a couple inches less in height. That should be worth some speed!

I’ve used both straight cranks (less Q) and flared cranks (more Q) on my 29er, and I’ve found that the flared cranks give me more leverage for side to side balance making me feel more stable. However, this is at the cost of more wobble to manage at higher speeds.