Q Factor: Measurement, Determination, and Adjustment

What Is Q-Factor?

Q-factor refers to the distance between the pedal attachment points on the left and right crank arms.

This distance depends on the length of the bottom bracket (BB) spindle and the shape or bend of the crank arms, so the Q-factor is essentially determined by the combination of BB and crankset you choose.

For Shimano cranksets, the Q-factor is typically listed in the crank specifications.

How Does Q-Factor Affect Riding?

A wider Q-factor results in a more bow-legged pedaling position, while a narrower Q-factor creates a more inward-legged position.

In cycling, a narrower stance allows your body’s center of gravity to align properly over the pedals, leading to more efficient pedaling. On the other hand, a wider stance spreads out your center of gravity, offering more stability and easier foot placement, but with some loss of power due to outward pedaling force.

As such, road bikes—where high cadence and steady pacing are common—tend to favor narrower Q-factors. Mountain bikes (MTBs), which often require dismounting and frequent foot placement on rough terrain, benefit from wider Q-factors for improved stability.

Even within road biking, the optimal Q-factor varies depending on the rider’s body. For example, riders with wider pelvises need a wider Q-factor. This is why smaller-framed female riders often end up pedaling bow-legged when using standard road cranksets.

Benefits and Effects of Choosing the Right Q-Factor

The biggest benefit of selecting the correct Q-factor is achieving a pedaling motion that fits your body.

For example, in road biking, the goal is to pedal at a steady cadence while seated, keeping your legs moving in a straight vertical path. This ensures that all your downward force is transmitted directly to the pedals. It also helps keep the bike’s center of gravity balanced, stabilizing your pedaling.

Additionally, in road biking where aerodynamics matter, a narrower Q-factor lets riders keep a more compact posture, reducing wind resistance.

On the other hand, in mountain biking—where riders often stand on the pedals or put a foot down—the center of gravity being too centralized can make the bike unstable, increasing the risk of falls. For this reason, MTBs are designed with wider Q-factors to maintain better balance on uneven surfaces.

How to Measure Q-Factor and Find the Optimal Size

Measuring the Q-factor is simple — it’s just the distance between the pedal attachment points. However, since the crank arms are offset from each other, you’ll need to rotate the crank while measuring with a tape measure or similar tool.

Once you’ve measured your current crank’s Q-factor, compare it to your ideal pedaling position to see if it’s too wide or too narrow.

Try pedaling without your shoes clipped in, and shift your feet 1 cm inward or outward to find the most natural position. Once you’ve found that position, calculate the difference from your current Q-factor.

If the optimal position is inward, subtract twice the shift distance. If it’s outward, add twice the shift distance to determine your ideal Q-factor.

How to Adjust Q-Factor

There are several ways to adjust Q-factor:

Let’s look at each method in more detail.

Replace the Crank

The most straightforward way to adjust Q-factor is by replacing the crank. This allows for a significant change in Q-factor, so it’s ideal when your current setup doesn’t suit you.

Each crank has a fixed Q-factor, so compare your current Q-factor to your optimal one and look for a crank that matches that spec.

If you’re switching to a narrower Q-factor crank, be sure to measure how narrow your bike frame allows. Just align the cranks parallel and measure the space between the crank arm and chainstay.

If this gap is too small, the new crank might interfere with the frame. To avoid this, leave at least 5mm of clearance.

Also, when replacing cranks, don’t forget to choose the appropriate crank arm length for your body and riding style.

Adjust with the Bottom Bracket (BB)

For standard square taper cranks, the bottom bracket has an integrated spindle, and various spindle lengths are available, allowing you to change the Q-factor just by swapping the BB.

For example, Shimano’s square taper BB model “BB-UN300” comes in lengths from 107 mm to 127 mm, letting you adjust Q-factor by up to 2 cm.

Note: Shimano’s Hollowtech II cranks have integrated spindles, so Q-factor cannot be adjusted via the BB in that case.

Adjust with Pedals or Cleats

You can also fine-tune the Q-factor by adjusting the cleats on your shoes — no need to change the crank. This method allows for minor changes (a few millimeters).

Just slide the cleats sideways on your shoes. Be cautious not to move them too much, as this can shift your pedaling center and reduce efficiency. This method is best for small tweaks.

Note: Time-brand clipless pedals don’t allow for lateral cleat adjustment, but you can swap the left and right cleats to adjust the Q-factor.

Using Crank and Pedal Spacers

If you want to widen your Q-factor, using crank or pedal spacers from third-party manufacturers is one option.

There are two main types of spacers: washer-type and bolt-extension-type.

Washer-type spacers allow for millimeter-level adjustments by stacking multiple washers. However, adding too many washers can prevent sufficient tightening torque or even damage your crank. Be sure to check compatibility with your crank and pedals before use.

Adjust Saddle Height and Fore-Aft Position

When narrowing your Q-factor, don’t forget to also check your saddle position. A narrower Q-factor can naturally bring your legs closer together while pedaling, potentially causing your inner thighs to rub against the saddle.

If you notice rubbing after narrowing your Q-factor, try moving your saddle slightly backward. This moves the saddle’s nose away from your inner thigh and helps reduce friction.

If friction persists, try lowering the saddle height or consider switching to a different saddle. Look for models with narrower noses or women-specific short-nose saddles as potential solutions.

If you’ve widened your Q-factor and your current saddle no longer fits well, switching to a saddle with a wider rear (tail) can improve pedaling stability.

Shimano Road Bike Crank Q-Factor Overview

Lastly, let’s take a look at the Q-factor specifications for Shimano’s road bike cranksets:

For race-grade cranksets from the 105 level and up, the standard Q-factor is typically 146mm. However, the latest DURA-ACE R9200 and ULTEGRA R8100 have widened slightly to 148mm.

In contrast, non-racing cranksets like TIAGRA and below start at around 150mm, and triple chainring models often reach around 158mm — over 10mm wider than race-grade cranks. This likely reflects the difference between racing and general-purpose designs.

If you want to narrow your Q-factor but are already using a 105 or higher crank, changing the crank won’t help. However, upgrading from a TIAGRA or lower crank to a 105 or higher can reduce your Q-factor by 2–13mm.