Q-factor is the horizontal distance between the outside of one crank arm to the outside of the opposite crank arm.

Stance width is the combination of this distance plus the distance from the crank to the centreline of the pedal body (sometimes also confusingly called Q-factor). This makes up the distance between pedal centres.

Why is Stance Width important?

As with many bike fitting topics, it’s all about alignment. A bike’s geometry is perfectly symmetrical, but we humans are not. Since the rider is literally locked to the bike via the pedals, we need to ensure the two are compatible.

An ideal Stance Width means your knees are positioned directly above the centre of the pedals throughout the pedal stroke. This ensures minimal side-loading on the knees reducing the risk of injury and increasing pedalling efficiency.

If the Stance Width is too wide or too narrow for your body’s natural stance (and range of motion), you can experience strain in your joints (often your knees), resulting in discomfort, which can lead to long-term issues.

How to check your stance width

To check if your stance width you need to observe the rider from the front and monitor how their knees track vertically whilst pedalling. This is typically done during a bike fit by using a vertical laser line. We use the laser line as a reference to monitor the knee’s tibial tuberosity (the knobbly bit below your kneecap) as it tracks up and down through the pedal stroke.

Ideally both knees should track vertically, following the laser line both in the up-stroke and down-stroke. This of course is rarely the case, since very few individuals are symmetrical in their skeleton and mobility.

Issues you may experience with improper stance include:

• Pressure on the outside of the feet: a narrow stance width can lead to excessive supination, causing pressure along the outsides of the feet. Some riders will mistake this for their shoes being too narrow.
• Medial (inside) knee pain: pain on the inside of the knees can often be due to insufficient stance width. This is often accompanied with knees that track outwards at the top of the pedal stroke.
• Lateral (outside) knee pain: Pain on the outside of the knees can be due to excessive stance width.
• Saddle discomfort: A stance width that is too narrow can result in excessive rocking on the saddle leading to rubbing and/or saddle discomfort.

How to Adjust Stance Width

As mentioned earlier, your stance width is determined by 2 elements: Crank width (or Q-factor) and pedal axle length. In fact, there is a third (albeit limited) variable: cleat position. Cleats can be moved medially or laterally. That is, in or out looking at the bike from the front or back.

We can avoid spending time discussing Q-factor for two reasons: firstly, changing chainsets is very costly. Secondly, the difference across manufacturers (within disciplines) is minimal. All road bikes have a Q-factor of around 145mm. Other disciplines have much wider Q-factors: MTBs have around 170mm, fat bikes can have 200mm+ to cater for wider tyres.

Option 1: Cleats

The first step to tune your stance width is to adjust your cleats:

• Inwards to increase stance width (cleat in, foot out).
• Outwards to decrease stance width (cleat out, foot in).

In my experience, most road-bike riders suffer from a stance width that is too narrow and so moving the cleats in should be the first step. However, the amount of movement in the cleat is small: only a few millimetres which is often not enough to allow the knees to track vertically over the pedal centres. In which case, you need to move onto option 2…

Option 2: Pedal spacers

The easiest way to boost stance width is to add spacers between your pedal and the crank. These come in two types:

• 1.5mm washers: these are stainless-steel spacers which move the pedals outwards as much as possible without compromising thread engagement.
• 20mm spacers: if washers aren’t enough and you have pedals that attach with a pedal wrench, then you might consider 20mm pedal spacers. This gives you a relatively cheap and safe way of extending pedal axle length.

Option 3: The final option is to change your pedals for ones with a longer pedal axle length. Some manufacturers only make one length, whilst others have a range. See below for data on the most common pedals.

Pedal Q-Factors

The width of pedals that contributes to your overall stance width is often also referred to as Q-factor. The measurements below are the distance from the face of the crank arm (where the pedal screws into the crank), to the centre of the pedal body (which aligns with the centre of the cleat).

Shimano

SPD-SL Cleats

• Dura Ace 9100: 52mm and 56mm
• Ultegra 8000: 52mm and 56mm
• 105 R7000: 52mm

SPD Cleats

• XTR: 52mm and 55mm
• PD-M540 & M520: 55mm

Look

• Blade, Max, Sprint, and Classic (all versions): 53mm

Speedplay

• Zero Titanium: 50mm
• Zero Chrome-Moly: 53mm
• Zero Stainless: 53mm
• Zero Stainless custom lengths: 50mm, 56mm, 59mm and 65mm

Other factors to consider

Without delving too deeply into the world of bike fitting, the ‘knees out’ rider may also have a saddle height issue or a need for foot wedges. If the saddle is extremely low, a similar pedal stroke will develop.

Crank length and its effect on a rider’s hip angle can also be another factor.

For riders whose knee falls inwards on the downstroke, this can also be a sign of insufficient arch support in their shoe insoles.

Conclusions

I always stress to bike fit clients that the foot-pedal interface is the foundation of a good bike fit. If stance width is incorrect, then problems can arise down the line. If a cyclist is out of alignment riding at 85 rpm, that’s 5,100 pedal strokes per leg, per hour. If the ‘average cyclist’ rides 6 hours per week, that is roughly 122,000 pedal strokes per month and over 1 million per year, per leg. With that number of pedal strokes, the strain on the body (especially the knee) is significant, making injury risk high.

If you need help with this, or any other aspect of your bike fit book online for a professional, bespoke bike fit session.