> Fit Guidelines
BikeDynamics - Bike Fitting Specialists
Bike Fitting Guidelines - Rules of Thumb
Knee Angle - MaximumThe ideal saddle height can be described by the angle of the knee at full extension. Typically, men will be close to 142° and women maybe 1-2° higher. The difference is due to flexibility, with looser female hamstrings allowing the knee to extend further. Tight hamstrings will inhibit the extension of the knee, so many people find that being less than 140° may suit them better. The key to finding the ideal saddle height is to use knee angles and hamstring flexibility to get close, then fine tune (up or down 1-2mm at a time) until in the ‘sweet spot’. Please note that these are dynamic measurements, i.e. whilst pedalling and that static measurements may be different.
See Saddle Position and Crank Arm Length
Knee Angle MinimumOnce the maximum knee angle has been established, the minimum should be checked. Avoid an angle less than 70° as this can put high shear forces into the knee joint, exaggerates the 'dead zone' at the top of the pedal stroke and can cause discomfort in the hip and lower back. If too tight, you will need shorter crank arms.
See Saddle Position and Crank Arm Length
Saddle set backThe simplest method for establishing saddle fore aft position is to hang a plumb line from the tibial tuberosity (the bony bump below your kneecap). This should pass straight through the pedal spindle when the crank arm is at three o'clock. This is called the Knee Over Pedal Spindle (KOPS) rule, but contrary to popular opinion there is absolutely no biomechanical justification for it. In fact, if the saddle height is incorrect the knee will be too far forwards or back and it will be wrong!
It can work very well though because it is a good predictor of the hip position relative to the seat tube axis. If the hip joint is along this axis, the rider will tend to be well balanced without too much weight on their hands and as the bike designer intended. Finding the precise point on the Greater Trochanter to signify the hip centre of rotation can be tricky though, which is why the KOPS technique is more popular.
See Saddle Position
Torso Angle - FastTorso angle is very dependent upon the cyclists choice of performance and comfort. A lower position is more aerodynamic as frontal surface area is reduced. 30° to 40° is performance orientated, but does rely on reasonably good flexibility to lower back and hamstrings.
Torso Angle - TouringA more relaxed torso angle will take the pressure off the lower back, hamstrings and neck. 40° to 50° is a suitable angle for longer distances where comfort is the priority over speed.
Minimum Hip AngleTorso angles significantly less than 30° can only be achieved using specific Time Trial or Triathlon bikes. Although being much lower at the front will reduce aerodynamic drag, the minimum hip angle can tighten to a point where both comfort and power are compromised. Note how there is a difference between the ‘actual’ hip angle measured between the body reference points and the ‘real’ hip angle due to the curvature of the spine. The ideal ‘real’ hip angle will vary between individuals and is dependent upon their flexibility and duration of events.
The ‘actual ‘ hip angle is easier to measure and men of average flexibility should be able to sustain 45° to 50° for some time. Whereas very flexible women such as World Champion Duathlete Helen Russell shown here can hold angles of less than 40°.
The minimum hip angle can be affected by saddle height and fore-aft position, crank length and the position of the bar extensions and elbow pads. Moving forwards onto the tip of the saddle will open up the hip.
See Time Trial and Triathlon Positions
Upper arm and elbowOn a road bike, the upper arm should always be between 80° and 90° to the upper body. This puts the shoulder in a relatively stable position and distributes loads directly into your skeleton. If ever fitting a shorter stem, care should be taken to check that knees do not hit the bars when riding out of the saddle.
A small bend in the elbows will help dissipate road induced shock load into your upper body. If you feel you need to ride with locked elbows, you are probably too far away from the bars.
Hand PositionDropped handlebars are designed to offer a number of holds to facilitate both alternative torso angles and a variety of hand positions. This is to suit different road conditions and prevent discomfort due to staying in one position for too long. Once saddle height and set back has been established, stem length should be set such that the hands fall naturally to the hoods. This offers the alternatives of a more relaxed position up on the bars and a more aerodynamic position on the drops. If riders spend nearly all their time up on the bar tops, either their top tube or their stem is too long for them. The hoods should be adjusted to give a neutral wrist posture (as when shaking hands), whilst ensuring good lever access on the drops.
Cleat PositionThe cleats should be positioned such that the ball of the foot is over the pedal spindle and to accommodate the natural toe in or out of the foot. The ball of the foot can be defined as the end of the metatarsal bones which can be found with a bit of light prodding. Alternatively just use the bony lump on the inside of the foot at the base of the big toe. There is little downside to cleats being too far back and numerous problems if forwards, so if in doubt, move the cleats back.
See Foot to Pedal
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