Q Factor: Measurement, Determination, and Adjustment

What is the Q Factor?

The Q factor refers to “the distance between the pedal attachment points on the left and right cranks.

The distance between the pedals depends on the length of the BB shaft and how bent the crank arms are, so basically the BB and crank you choose will determine the Q Factor.

If it is a Shimano crank, the Q factor is listed in the crank specs.

How does the Q factor affect the ride?

Basically, a wider Q-factor results in a more gangly pedaling style, while a narrower Q-factor results in a more inward pedaling style.

In bicycling, pedaling efficiency is higher when the inner thighs are inward, because the body’s center of gravity can be properly applied to the pedals. Conversely, the more you have your legs spread apart, the wider your center of gravity is, the more stable you are, and the easier it is to keep your feet on the bike.

Therefore, the Q factor is narrower for road bikes that require a constant pace and high cadence, and wider for MTBs and other bicycles that require standing pedaling to increase stability.

Also, the appropriate Q factor for the same road bike will vary depending on the person riding. A person with a wider pelvis will have a wider Q-factor, which is why a petite woman will end up with a gangly leg if she uses the cranks of a standard road bike.

Benefits of Choosing the Right Q Factor

The greatest benefit of choosing the proper Q-factor is that pedaling fits the body.

For example, if you are on a road bike, you pedal at regular intervals on the saddle, so that the pedals are directly under you with your legs straight, you can transmit the force of your steps to the pedals without leaks. It is the sensation of lifting your knees straight up and down. The center of gravity of the bicycle is in the middle, which makes pedaling more stable.

Also, since aerodynamic drag is an important factor in road biking, a narrower Q-factor will allow you to fold your body into a riding position, which will also have a positive effect in terms of aerodynamic drag.

On the other hand, on MTBs, where there are many dancing scenes and one-footed movements, it is easier to lose balance if the center of gravity of the bicycle is closer to the center of the frame. For this reason, MTBs are set with a wider Q factor to emphasize stability on rough roads.

In this way, the choice of Q-factor differs depending on the intended use.

How is the Q Factor measured? What is the optimal size?

To measure the Q factor, simply measure the distance between the pedals. However, since the cranks are alternating, you should measure the distance by rotating the crank on the bicycle while applying a measuring tape.

Once you have measured the Q-factor of your current crank, compare it to your optimal position to see if it is too far out or too far in.

Try pedaling with your shoes unfastened on the bindings and shift them inward or outward by 1 cm to find the most natural pedaling position. Once the natural position is found, determine the difference from the current Q-factor.

If the correct position is inside, double the distance shifted and subtract, if outside, double the distance shifted and add.

How to Adjust Q Factor

Change the crank

The quickest way to change the Q factor is to replace the crank. In many cases, changing cranks can significantly change the Q-factor, so this is the method to try when the Q-factor of the current crank does not fit well.

Since the Q factor is determined for each crank, find out the Q factor of the current crank and the appropriate Q factor for you, and then find a crank that is close to that specification.

If you are replacing a crank with a shorter Q-factor, you should also measure how much Q-factor your bicycle can tolerate. The measurement is simple: just parallel your current cranks and measure the gap between the seat stays.

If you do not choose a crank with a good measurement here, you will not be able to turn the crank due to interference with the chainstay when you replace the crank. It is advisable to allow at least 5mm of clearance to allow for the risk of interference.

In addition, if you change cranks, the crank length is also important, so do not forget to choose the crank length that suits you.

Adjustment by BB

This is not possible with Shimano’s Hollowtech II cranks, but with common square BB cranks, the Q-factor can be tightened simply by changing the BB, since various shaft lengths are available for the BB.

For example, Shimano’s square type BB, BB-UN300, has a lineup from 107mm to 127mm, so the Q factor can be changed by as much as 2cm.

Adjustment with pedals and cleats

Even without changing the Q factor of the cranks, the Q factor can be adjusted with cleats within a range of a few mm.

The procedure is simple: simply move the position of the cleat attached to the shoe laterally. If the position of the cleat is shifted too far, the center of gravity when stepping on the shoe will be shifted, so the cleat should only be used to adjust the Q factor by a few millimeters.

Note that Time’s binding pedals do not allow lateral adjustment of the cleat position, but instead allow Q-factor adjustment by swapping the left and right cleats.

Let’s also adjust the saddle!

When the Q-factor is tightened, the inner thighs may rub against the saddle as the rider naturally pedals with the inner thighs.

If the Q-factor is too tight and the saddle starts to hit the rider, try moving the saddle back. This will bring the nose of the saddle next to the inner thighs and reduce friction.

If you still experience rubbing, consider replacing the saddle. One option is to choose a saddle with a narrow nose section or a short nose saddle for women.

If the saddle no longer fits you due to a wider Q-factor, replace it with a saddle with a wider tail section to stabilize your pedaling.

Summary of Q-factors for Shimano cranks for road bikes

Finally, let’s look at the Q-factors of Shimano’s cranks for road bikes.

For racing grade 105 and above, 146mm is the standard, with the latest DURA-ACE R9200 and ULTEGRA R8100 widening by 2mm to 148mm.

On the other hand, cranks for non-racing grade TIAGRA and below are based on 150mm, and front triple cranks are around 158mm, which is more than 10mm (1cm) wider than 105 grade cranks and above. This area is probably the difference between race-spec and non-race-spec cranks.

If you want to increase the Q-factor and your bike is already equipped with 105 or higher grade cranks, you cannot make any changes by changing cranks. However, if you upgrade from TIAGRA or lower cranks to 105 or higher cranks, you can tighten the Q-factor by 2 to 13mm.