Getting the correct frame size
In order to make effective use of your fitness the riding position on your road bike must be correct. This involves the optimum setting of your three points of contact with the bike: the pedals, the saddle and the handlebars. To be able to set properly these points of contact, the first requirement is a bike frame of a size that is suitable for you. The best way of achieving this is in consultation with a good frame builder who has experience of building all types of bike frames. The frame builder will be able to advise on the proper frame size and angles to suit both you and the type of event for which the bike is intended. However, these notes may be useful if you want to provide the frame builder with some information and later when you come to set up your riding position.

Estimating seat tube length
The two main measurements required for a correctly sized road frame are the seat tube and top tube lengths. These, together with the seat tube angle are the parts of the frame most influenced by your body size, and are shown in Figure 1. Top tube length is generally taken to be the horizontal distance from the centre line of the head tube to the centre line of the seat tube, whilst seat tube length is the straight line distance from the centre of the bottom bracket to the centre of the junction between the seat tube and the top tube.

Note that the seat tube angle shown in the figure is for a horizontal top tube and a straight seat tube. With a curved seat tube you would have to take an imaginary straight line from the centre of the bottom bracket to the top of the saddle midway between its front and back edges, whilst with a sloping top tube the angle would be that for an imaginary horizontal top tube.

To estimate the correct seat tube and top tube lengths for your road bike several measurements of your body and limbs will need to be taken. The first of these is your inside leg measurement. This is taken with you in a standing upright position, without shoes and with your feet about 25cm (10") apart. The measure is then taken vertically from floor to crutch (the point on the crutch where the measurement is taken from is the bony protuberance known as the ischial tuberosity - the lowest part of the pelvic bone - that you sit on).

The seat tube length is calculated as being 2/3rds of your inside leg measurement. Thus, if your inside leg measurement was 84cm (33") the seat tube length would be 56cm (22"). A list of typical inside leg measurements and estimated seat tube lengths is shown in Table 1.

Top tube length
The top tube length of your bike should be proportional to a combination of your trunk length and arm length. The required measurements for trunk, forearm and total arm lengths should be taken as shown in Figure 2.

For these measurements you need to be seated with your back pressed firmly against an upright surface such as a wall. Trunk length is measured from the seat you are sat on to the top of your shoulder with you sitting fully upright. The forearm length is measured from the back of the elbow to the centre of your clenched fist. Total arm length is obtained with your arm straight out in front and measuring from the upright support to the centre of your clenched fist (keep your back firmly against the support). The measurements are used in the following equation.

The answer should be rounded out to the nearest 1/2cm (1/4")

Seat tube angle
For this angle you first of all need to measure your thigh and lower leg lengths. Thigh length is measured horizontally from the upright support to the front of your kneecap, whilst the lower leg length is measured from the top of your kneecap vertically to the ground. Then calculate the seat tube angle as:

The answer should be taken to the nearest 0.5 degree. Table 2 gives some examples of seat angles for various combinations of thigh and lower leg lengths.

Setting the correct riding position
There are a number of basic settings for various parts of your bike that allow your correct riding position to be set up. These include the setting of the foot on the pedal, the saddle height, the forward and backward movement of the saddle on its pillar, and the positioning of the handlebars and brake levers.

Foot position
Whether you use toe clips and straps or clipless pedals the shoe plate should be set so that the ball of your foot (the large joint of your big toe) is directly over the centre of the pedal spindle, as shown in Figure 3.

If toe clips are used it may be necessary to either pack them out if they are short, by putting washers between them and the front plate of the pedal, or put them behind the front plate of the pedal if they are a bit too long. Generally speaking they should be set so that they barely touch the front of your shoes.

Saddle height
The height of the saddle is normally measured from the centre of the pedal spindle (with the cranks in line with the seat tube) to the top of the saddle at a point midway along its length. This length will not only be affected by inside leg length, but also by natural riding style. For example, some people have a heel-down position with the foot at the bottom of the pedal stroke, and for them the saddle height would be lower than for someone with the same inside leg length who adopts a heel-up pedal position. However, for all riders the leg is never completely straight when the foot is at the bottom of the pedal stroke, as seen in Figure 4.

As a starting point the simplest way to estimate saddle height is to calculate 107% of your inside leg measurement as described earlier. After that it may be necessary to make some adjustment to take account of your own individual riding style.

Forward and backward movement of the saddle
The forward and backward movement of the saddle should be set so that, with the cranks in the horizontal position and with you sat on the saddle in your normal riding position, a vertical line could be dropped from just behind your kneecap to intersect the centre of the pedal spindle (see Figure 5). This will ensure that your legs are in their best position to transmit the power of your muscles into the pedals.

Position of the handlebars
Handlebars are available in a variety of different sizes and widths. Whilst the shape may be decided by personal preference, the width should be equal to the width of your shoulders. Setting the position of the handlebars on the bike requires having a handlebar stem of appropriate length, and setting the top of the handlebars a certain distance below the top of the saddle (see Figure 1).

These will be affected by your arm length, the flexibility of your back in allowing you a low aerodynamic position, and the amount of elbow bend you prefer when riding "on the drops" of the handlebars. As a starting point, to estimate the required length of handlebar stem use the following equation.

To set the top of the handlebar a suitable distance below the top of the saddle, the following method may be used. First, set the handlebar stem so that there is about a 25mm (1") gap between the underside of the stem and the top of the steering column assembly. Then, with you in your normal riding position on the bike and with your hands gripping the handlebars in the middle of the bend (as in Figure 5), bend your elbow until your lower arm is parallel with the ground. In that position there should be a 90 degree bend in your elbow joint. Another check is for you to sit up with your hands resting on the top of your handlebars. From this position it should be difficult to see your front wheel spindle because it is obscured from view by the handlebars.

Two other points with regard to the handlebars is that the bottom of the 'bars should slope backwards and downwards, as in Figure 6, to allow a more natural slope to your wrists when riding "on the drops". Secondly, the brake levers should be set so that they slope forwards and upwards. This gives your hands a comfortable position on the brake hoods when riding "on the tops".

Final points
It is worth remembering that the calculations used to estimate frame size, and the advice given here on setting up your riding position are generalisations based on average figures calculated from measurements on a wide range of riders. Within those averages there are variations typical amongst a group of people. Therefore, no formula can give the perfect frame size and riding position for every rider.