• Ultra Sports

A simple guide to correctly fitting your bike

Updated: Feb 10, 2019



A number of our patients at Ultra Sports Clinic are cycling for 10-20 hours a week at a rate of 80-120 rpm. That’s between 48,000 and 144,000 lower limb repetitions per week.

With this is mind, we thought it would be a good time to discuss the biomechanics of cycling. Understanding cycling biomechanics is beneficial for two main reasons:

  • You can cycle more efficiently

  • You can decrease your risk of injury.

So, let’s take a look at how to properly set up your bike.

Note: it’s always best to set up the bike once you’re warmed up.

Step 1: Seat Height

Seat height is an essential aspect of bike set up. If your seat is too high, power output is decreased as muscles are forced to work beyond their optimal length-tension relationship. Moreover, structures of the posterior chain (hamstrings, gastrocsnemius and posterior knee joint capsule) have an increased amount of stress placed on them.

Furthermore, if the seat is too high the rider will often rock side to side in the saddle which unnecessarily fatigues the adductors, gluteals, spine and muscles of the upper body.

On the contrary, if the seat is too low – knee flexion increases. This places additional stress on the patellofemoral joint and the suprapatellar bursa. Moreover, it affects the length-tension relationship of the gluteal, hamstring and calf muscles thus reducing your efficiency.

So how do you work out what seat height is ideal for you? You can use the ‘Le Mond’ method, which was formulated by American cyclist Greg Le Mond.

You start with the in-seam measurement (diagram 1).

  1. Remove shoes and stand 4” to 6” apart

  2. Place a book between your knees as high as you comfortably can

  3. Measure distance from floor to the top of the book


Figure 1

Once you have measured your in-seam, the next steps is to multiply this number by 0.88. Once you have this measurement, apply it to your bike from the middle of the bottom bracket to the very top of the saddle.


Figure 2

Other factors which may affect seat height include:

  • Type of seat

  • Seat position (fore/aft)

  • Cleat position (fore/aft)

  • Crank length

  • Personal preference

Step 2: Seat fore/aft position

Much like seat height, seat position can play a large role in injury and efficiency. If your seat is too far forward, additional compressive force is placed on the patellofemoral joint. If your seat is too far back, the power of the hamstrings and glutes is diminished.

So how do you measure ideal fore/aft position? All you’ll need is a plumb bolt.

  1. Sit on the bike on a level surface

  2. Spin pedals until knees are at 90 degrees (the 3 O’clock position)

  3. Drop the plumb bolt from the tibial tuberosity (just underneath knee cap)

If the bolt lands either over or behind the pedal axis, seat position is good. If the bolt lands in front of the axis, this position will lead to increased loading of the patellofemoral joint of the knee.

Step 3: Cranks

Crank size needs to be relative to leg length (trochanteric height to be specific). Generally speaking, cranks are only an issue in shorter and taller riders – those who are average height are not affected by crank size.

In smaller riders:

  • 160 cm (5 ft 3 in.) – 165 cm (5 ft 5 in.)

  • 170 length cranks or less

  • < 160 cm (5ft 3 in.)

  • 167.5 or 165 cranks

In taller riders:

  • >180cm (6 ft)

  • 175 cranks

Step 4: Cleat Positioning

Cleat positioning aims to properly align the hip, knee and ankle. Cleats move in 3 directions, each of which contributes to alignment. These are:

Fore/aft

  • The base of the 5th metatarsal (bottom of the little toe) should sit over the pedal axis

  • This increases efficiency by utilizing maximum foot power

Medical and lateral

  • Narrow hips should have medial (inwardly) positioned cleats to maintain alignment

  • Broad hips should have lateral (outwardly) positioned cleats to maintain alignment

Rotation

  • Most people are fine with toes pointing straight ahead

  • If the rider naturally has a toe-out position, cleats can be turned out accordingly

Step 5: Reach

An ideal reach can increase your control of the handlebar for more responsive handling. If your reach is too long, you may not be able to reach the brake levers from the drops.

If your reach is too short, you are forced into a slouched position which can lead to neck and shoulder pain or even hand numbness.

There is no official measurement tool for this as it depends a lot on rider flexibility, comfort and experience. The images below demonstrate the difference between a good and bad reach set up.


Figure 3: Example of a good reach, courtesy of Brukner & Khan


Figure 4: Example of a poor reach, courtesy of Brukner & Khan

The key with cycling is to work smarter rather than harder. If you feel like you would benefit from a proper bike fit, or have an injury related to cycling, call Ultra Sports Clinic today.


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+44 20 3893 5100

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