Crank Length

Crank Length

Crank Length

Why Crank Length Matters

Cyclists buying a new bike, look for the correct frame size but just as critical is the optimum crank length. This article explores why.

Crank length is the length from the centre of the bottom bracket to the centre of the pedal axle. Most bikes are fitted with a 170-175mm crank. The size range available can stretch from 140-190mm with a little searching amongst different manufacturers.

Last year I did a cycle fit for a triathlete visiting us for a training week. Their coach wanted them to optimise their position, and improve their potential run off the bike.

I asked if the crank length, had been deemed optimal by their coach and previous fitter. “I think so, it’s what has always been on the bike.” was the reply.

Watching as they pedalled, I saw their hips move to allow the knee space to clear the ribs and I watched as their hips dropped to facilitate the bottom of the pedal stroke.

The solution was not just a bike fit but a change to a shorter crank.

Speed = Comfort + Power + Aerodynamics

Comfort in cycling terms can be defined as the ability of a rider to sustain their optimum position for the duration of a ride.

Power is the ability to apply force to the pedals without restriction within a range of accepted biomechanical norms.

Aerodynamics are achieved by optimising frontal surface area and shape to minimize resistive forces of air.

Crank length is all too often overlooked. Over time the crank length on a given size frame has become accepted as a norm. There is no particular basis for the current default standards applied by cycle manufacturers.

Size ranges that are readily available and supplied to bike companies are based on what is popular. It would be better if they are based on the specific science and research.

One major bike manufacturer works on a basis of no options available in crank length, on a given size. If you buy a frame of a given size say a medium you get a crank of xxx mm. If you want a different crank length, you need a different size frame. That now means that the geometry may be wrong for you. Alternatively you can purchase a new crank set of the correct length for approximately €300.

We were impressed when Kate bought a new BTB bike last year from a manufacturer that did offer a choice of two crank sizes for her size of frame.

The Difference Crank Length Makes

The crank arm creates the pedalling radius from the bottom bracket. A shorter pedal crank will make a smaller circle. The implication is that the foot won’t move so far up and down. Less range of motion for the leg to travel through, this affects all the key joints in the lower body.

There are optimum ranges of motion for these joints depending on the bike you are on. Opening the hip angle can lead to improved power and aerodynamics. Some research indicates that for triathletes, this may lead to a better run off the bike.

Athletes have three touchpoints on the bike: saddle, handlebars, and pedals. Many athletes can recognise the difference that saddle and handlebars make on their position. They often think about pedals as simply about their brand or type of choice. Many don’t think about the part that connects the pedals to the bike: the crank arm.

What Crank Length Is Right For Me?

As with all talk about bike fit, these are individual changes. There is not a one size fits all solution. Personal mobility, flexibility, biomechanics, and experience all impact any decision about crank length.

Research indicates that 20% of leg length or 41% of tibia length is a starting point. This is more specific than a manufacturers’ default, of length by particular frame size.

Additionally consider the crank length, compared to the saddle height, to the bottom bracket. This ratio is likely to be specific to the rider, their proportions, and their mobility.

To date, there is no ‘standard’ answer. For triathletes, consider how efficiently and effectively you can run off the bike.

Check what cranks your bike came with. Consider whether you have enough space at the top of the stroke. Can you move cleanly through, without excess load or changes of angle to the hip? If not, possibly consider that switching to a shorter crank length may help.

If you’re about to buy a new bike, discuss with your local bike shop as to your options. Take time to consider what different manufacturers offer.

Possible Problems With Cranks That Are Too Long

  • Seat position must be lower in order to not overextend the leg at the bottom of the pedal stroke.
  • If the seat position is not lower, excessive hip rocking can occur with instability at the saddle contact point.
  • Inability or difficulty in spinning a high cadence.
  • The knee has to go higher at the top of the pedal stroke just to get over the pedal.
  • The angle between the knee and the chest is reduced with the knee coming closer to the chest. This may be impacted by individual athlete mobility issues and physical dimensions.
  • Difficulty breathing.
  • To assist with increased leg motion, the ankle may compensate (or increase range of motion) to facilitate movement.
  • Compensation may occur at the hip to enable the knee to clear the chest.
  • Some riders may experience a limited difference other than overload on associated soft tissue. Triathletes may benefit by reducing or minimising any excessive loading to avoid any issues caused on the bike from showing up on the run.

Using A Shorter Crank Can Offer Advantages

  • Comfort: a shorter crank length reduces range of motion at the knee (extension and flexion), hips, and low back.
  • Power: shorter cranks alone will not increase power output but they can reduce restrictions through the top of the pedal stroke. This is by opening up an impinged hip angle and/or reducing knee flexion.
  • Aerodynamics: a shorter crank, subject to individual mobility, may allow you to ride at a lower angle. In turn this may minimise frontal surface area improving aerodynamics.
  • May reduce pain or excess discomfort in hips, knees, or lower back. This is due to decreased loading of specific joints, especially the hip flexors.
  • Mountain bikers may benefit from a decreased time to reach peak power and increased ground clearance.
  • Research on the topic of crank length showed negligible difference in power produced. However with shorter cranks there was significantly less oxygen requirement.

To summarise there is no one size fits all. There is not a specific length for an individual or an ideal for certain disciplines. If there is nothing wrong with your current crank size, then don’t change them.

As a rider be curious and consider a review of your bike fit. Exploring the option of crank size is part of a good bike fit.

Potentially the biggest downside is the cost of replacing your cranks if you decide you need to go smaller. The benefits of an improved ride position, experience, and results may happily offset this.

If you do change, remember to make the necessary adjustments to saddle height and fore and aft position.

Give yourself time to adapt to a new position before your next race, event, or big cycling adventure.

Enjoy your cycling comfort and efficiency … and have fun!

It’s All About The Saddle

It’s All About The Saddle

It's All About The Saddle

The most significant contact point that you can get right on your bike is the saddle. If your bike fit is correct, your saddle will be taking the largest percentage of your weight and will be offering optimum support. If support is inadequate, too much weight will be going through some of the rider contact areas on the saddle or through other contact points, creating problems.

The saddle that comes with your new bike is like most mass sold items, designed to generically fit people of the average size/build of the bike purchased and simply finishes the bike within a price point. It is not necessarily the best saddle for you.

What are some of the factors to consider in a saddle?

Support

The saddle carries most of the weight of the body. As the pelvis is not that large, it has only a small amount of contact area with the saddle. This contact is not like sitting in a chair. It is essential that your choice of saddle enables the most contact area available. This means that widths in different parts of the saddle are important.

It is crucial that you select the best saddle, in shape and design, for your individual build. If the saddle is not wide enough to support the pubis, riders twist to one side causing uneven loading, knee angles change causing loss of pedalling efficiency and potential shear forces. Get it right and the saddle increases comfort, efficiency, and performance.

Stability

Saddle design is also important for good rider biomechanics, which is key to maximising efficiency. Consider what shape of saddle best suits your riding style and sporting aspirations. The right saddle for you will provide stability. Being stable avoids the power output drop and performance or riding deterioration which instability causes. Stability creates the opportunity to improve power, speed or aerodynamic position.

Comfort

The wrong saddle can cause a range of other issues from simple discomfort to saddle sores or vascular problems. Saddles that cause a ‘hotspot’ result in riders shifting weight to the other side for relief. As a result, as they do so they place extra stress on the knees as they then track differently, placing unnecessary shear forces on joints. Repeating that thousands of times in a ride or race increases the risk of injury.

A poor choice of saddle or poorly positioned saddle results in riders shifting on the saddle to get comfortable. As a result, each shift causes a break in the pedalling rhythm. Each break in rhythm causes a loss of time. Research has found that at elite level each shift causes a time loss of approximately 3 and 1/2 seconds and is a lost quality pedal stroke. This means that not only is there a time penalty but also a negative energy cost.

Aero-friendly

The saddle is possibly the piece of equipment that most affects your aerodynamics. If a rider can’t hold an optimal position, the aerodynamics of the rider will affect drag coefficient negatively. For example, this will result in loss of gains made from expensive deep section wheels or other purchases. Riders and triathletes will discuss aerodynamic gains all day. However, the bigger gains are stability, comfort and efficiency. When you have stability you create the opportunity to improve power, speed or aerodynamic position.

If you cannot rotate the pelvis anteriorly it will be difficult to maintain an aero position or to be riding in the drops. Therefore the often-seen option of lowering the base-bar or slamming handlebars is not a positive choice. Without stability on the saddle it’s difficult to hold a quality aggressive or aero position.

Triathlon-Specific Considerations

Triathletes often wish to stay aero for as long as possible but if the saddle doesn’t suit the rider, it’s hard for them to rotate the pelvis anteriorly. This rotation is important to create that necessary stability in the position. An uncomfortable saddle will limit ability to maintain that position due to discomfort caused and pressure on nerves and blood vessels.

This results in posterior rotation of the pelvis to relieve the pressure, coming back to the base bar position and toughing it out in a poor position. This can cause excessive loading on the lower back which in turn affects the whole of the posterior kinetic chain.

For triathletes, any problems created on the bike section can also later cause problems on the run when loading on the body and the damaged area increases dramatically.

Individuality

There are some differences to consider between female/male pelvis size and width. Females generally have wider pelvises. However it’s important to consider yourself as an individual rather than making gender assumptions. It’s about finding the right saddle for you as a rider. What is the width of your pelvis? This is measured by the distance between the ischial tuberosities, the ‘sit bones’.

Other questions might include: Do you need more stability? Do you genuinely have the flexibility to use a certain type or model of saddle?

Knowing how you load your saddle is important. Do you load to the front, middle or rear of the saddle? Knowing this also helps inform saddle choice. You may need to ensure sufficient leg clearance to stop your knees angling out or poor rotation of the pelvis and increased positional shifting.

Cycle-Fit

Once you have the right saddle, also getting the height of the saddle right is essential. Power transfer is never going to be optimum if your saddle  is too high. Saddle height being too high, perhaps to emulate what the rider perceives to be the optimum position, can lead to the rider having to tilt the saddle nose down to reduce unwanted pressure.

In turn this causes instability as weight slips forward, increasing pressure on the front of the pelvis and causing discomfort. It can also place too much weight forward affecting, shoulders, back, arms or hands, and lead to other issues.

In Conclusion

Saddles are a hugely personal item of equipment. Spend the time to learn what suits you, get someone to assess your position critically. Get measured to have an optimum width to offer stability. Review your options regularly. Some manufacturers have test saddles you can borrow from retailers and others offer a 30 day trial or return. Time invested in getting it right will be rewarded with your goal of comfort with increased efficiency and performance.

Ian is a qualified cycle-fitter with over 10 years of experience working with age group and elite level riders/triathletes of all ages. He believes he is fortunate enough to have been trained by some of the best fitters in the business. His fitting knowledge is supported by his understanding as a Level 3 High Performing Triathlon Coach and a British Cycling Level 3 coach for Road, Time Trial, and MTB.

Ian is an age-group athlete, has represented GB at Long Distance and Cross Triathlon, and has completed over a dozen multi-day long distance cycling events. He is always happy to discuss your needs in relation to fit and training. Please get in touch with any questions.

Behind Bars

Behind Bars

Behind Bars

To Be Exact, Behind Handlebars & Aerobars

As with all your contact points on the bike, it’s important that your bike fit is optimised to enable a great position without the cost of comfort. If comfort is not there, efficiency is affected and so, therefore, is speed.

I am sure most of us who ride a bike have experienced that feeling of pins and needles in the hands, often along the ring and little finger. You take your hand off the bars, make a fist, wave your hand around and the sensation reduces and disappears. Hands back on the bars, back up to speed, and a while later it is time to repeat the process. On each occasion, whilst you do this, you reduce your speed (not to mention that one-handed cycling causes changes in ride posture/pressure on other contact points).

Clinically, this is known as Handlebar or Cyclist’s Palsy. It is commonly associated with compression of the ulnar nerve. The median and ulnar nerves provide sensory innervation to the hand. Compression most frequently is in an anatomical space in the wrist called the Guyon’s Canal. Depending on your choice(s) of hand position on the bars and the setup of the front end of your bike, numbness may also be experienced around the thumb, index, or middle finger. This will be compression of the median nerve and may be diagnosed as Carpal Tunnel syndrome. This is more common among mountain bikers and the cross -triathlon community due to the different handlebar configuration and hand position.

For triathletes, from novice to experienced, there then comes the question of aerobars. Incorrectly set up aerobars increase the risk of ulnar nerve impingement at the Cubital Tunnel at the elbow. As the ulnar nerve travels from the neck to the hand, compression of the nerve may show symptoms along this path. Most often symptoms are numbness and tingling in the hand or finger of the affected side and difficulty in the application of finer motor skills i.e. changing gear in an aero position.

Handlebar Palsy can be split into four categories, with a fifth category to consider in relation to aerobars, according to where the compression occurs. Each has its own characteristics of sensory loss and/or motor weakness. While it is unusual for age group triathletes and cyclists to suffer motor impairments, any symptoms and their causes should be managed to avoid the risk of long-term chronic damage.

Research in this area over a number of studies indicates that this is an important issue for a growing number of athletes riding on aerobars. Cross-referenced studies have shown increases between pre-event and post-event symptoms and end-of-season symptoms have shown a further increase. Triathletes and Time Trialists should research or take advice on the best shape of aerobar design and configuration for their individual biomechanics.

There may be a range of reasons for the symptoms across all groups of riders including:

  • Being too far forward on the bike – uneven weight distribution
  • Too much pressure through the hands
  • Incorrect grip on the bar
  • Incorrect athlete position on aerobars
  • Aerobar pads with insufficient or worn padding
  • Saddle too high/bars too low
  • Worn down handlebar tape
  • Poor saddle choice/position
  • Lack of padding in gloves
  • Incorrect bar width
  • Incorrect aerobar design for particular athlete
  • Incorrect aerobar set up – angle, width
  • Overinflated or narrow tyres

Due to the changes in how we train with the increasing numbers using turbo and smart trainers, a growing variety of platforms to train and race on, plus virtual racing events, the prevalence amongst the triathlon and cycling community may be on the increase. Historically there is an increase in people experiencing symptoms over the winter months. This is most likely due to decreased changes in hand position, less movement of the hands generally, and reduced fine motor movement demands. Training indoors may bring on symptoms due to factors such as wearing different or no gloves or moving less on an indoor trainer.

This condition can be caused by a poor bike set up/fit. I often see riders with stems slammed low to emulate a perceived quality aero position when the rider just is not capable of maintaining it comfortably, safely, or efficiently. As a result, weight shifts in different proportions around the contact points. The most common hand positions for symptoms are hands on the hoods or drops or by the gear shifters. Also, for those on aerobars, the general considerations for handlebars apply to the base bar but also consideration of the design of the aerobars and set up plus individual biomechanical limitations.

What can you do to relieve or stop the symptoms?

  • Get a proper fit.
  • Talk with your fitter and ask their rationale about changes to your set up.
  • Optimise your handlebar width for your physical size.
  • Optimise your aerobar design and shape for you.
  • Make small changes in angle to your handlebar position to reduce pressure on the hands.
  • Make sure to change hand position every 5-10 mins – especially when on the trainer.
  • Avoid over-gripping the bar – an overly tight grip does not improve your handling or security.
  • Reflect on your ride position and grip.
  • Ride a wider tyre or adjust tyre pressure.
  • MTB riders / Cross athletes should keep your front suspension serviced.
  • Gloves with foam/silicone inserts. Research indicates 3mm of foam to be effective.

Most of us who cycle will experience this from time to time. It is about noticing it, reflecting on it, and making those changes to improve your position or riding habits to maximise your health and the riding experience.

Ian is a qualified cycle-fitter with over 10 years of experience working with age group and elite level riders/triathletes of all ages. He believes he is fortunate enough to have been trained by some of the best fitters in the business. His fitting knowledge is supported by his understanding as a Level 3 High Performing Triathlon Coach and a British Cycling Level 3 coach for Road, Time Trial, and MTB. He is always happy to discuss your needs in relation to fit and training.