When sizing a bike it is helpful to understand that you are not just buying a bike off the floor in your size and all will be OK. For the bike to feel an extension of yourself we may need to make changes to your ride position. Altering the seat and handlebar will make the bike feel totally different. There is no absolute correct ride position for everybody as position is very individual. The guidelines to fitting a road bike usually requires precise fitting because you are in one position for long time, with considerations of breathing, aerodynamics and comfort, whereas an MTB covers extreme variation in terrain and the rider is in a multitude of riding positions, therefore the concerns are comfort and handling, not aerodynamics.
When purchasing a bike from Cairns Bicycle Works, you do not need to worry about fitting. As part of our sales service, we will correctly fit you to your bike, testing variations until you are happy with your ride position.
Seat to crank relationship
Your knee should have a 5 to 10 degree bend at full leg extension with your ankle relaxed
(See figure 1 (a)). Some riders choose to ride a slightly lower seat height however riding at a higher height can be harmful.
You may achieve the correct seat height on 2 or 3 different frame sizes therefore the seat height may not determine the ideal size bike for you. A way to estimate your seat height fairly accurately is to measure your maximum inseam with your cycling shoes on and multiply the measurement by 0.883. Apply this length to the centre of you cranks and your seat.
(See figure 5). You can check for accuracy making sure you are able to pedal with your heels on the pedals without pelvic rotation.
Centre weight balance
After we have your seat height correct and before we work on your handle bar position it is a great idea to see where your centre of balance is. We dont want too much weight on your handlebars. While your cranks are in a level position (9 & 3 oclock) we run a vertical line from the bump below your kneecap, we then adjust your seat forward or back until the line runs through the pedal spindle. If you are too far forward it puts more weight on the handlebar however makes the bike a bit better for sprinting (road use) or gives you more room to move back over the seat on rough terrain (MTB use). Back a bit can make the bike feel a bit more relaxed on longer rides and take weight of the bars however your upper leg will need to work harder on climbs.
(Figure 6).
Handle Bar to seat relationship
This is the part that is entirely up to you. Try different positions until you find a back angle that feels comfortable. (See figure 1 (b)). Our fitting staff have ways of measuring handle bar position to suit the type of riding you will be doing from free-ride jumping to triathlon however it is ultimately you that determines the fit.
The handle bar assembly can be adjusted in both directions and/or replaced to fine tune your position (See figure 1 (c)). We can offer a 90mm to 130mm stem length without affecting the handling characteristics of the bike too much however if you require a length outside this parameter we may look at a different size bike. This suggests that the frame length determines the ideal size frame that will suit you not the stand over height. A higher and closer handle bar position is more preferred by recreational riders whereas a lower position is preferred for performance.
Many riders complain about a sore neck. If your seat position is correct it you will be trying to shorten the head stem or raise the handle bars. There are different riding techniques that will help you transfer some load to your arms not your neck and shoulders by doing a small exercise;
Most women generally have proportionately shorter torsos, narrower shoulders, smaller hands, longer legs, longer thighs, shorter feet, and a wider pelvis than the average man. Therefore, a typically proportioned woman who buys a regular bike primarily designed for men may well discover the following results:
1. Longer Thighs
Too steep a seat tube which makes proper positioning the seat difficult. This can produce stress on the knees, reducing pedalling power.
2. Shorter Torso
Too long a top tube produces a stretched out position. This can produce low back pain and excessive crotch pressure as well as other problems.
3. Narrower Shoulders
Handlebars too wide and deep creating pain in the shoulder, upper back, and neck.
4. Smaller Hands
Handlebars too long and deep creating an inability to reach the brakes and shifters.
5. Wider Pelvis
A mans saddle is usually so narrow that a womans sit bones will slide over the outside edges of the saddle. This produces an effect much like straddling a gymnastics balance beam. The excessive pressure on the labia can produce soreness, serious inflammation, and cysts. A wider pelvis may also require that you use a cycling shoe and cleat system that allows side to side adjustment. You may also require a wider pedal axle.
It is likely that we will address The headset which offers vertical adjustment and it should be higher for women than men. The stem's horizontal length should be shorter on a women's bike than on one for a male of the same height, as both are determined by arm length. Arm length varies substantially between women and men, so the optimal bar placement varies a great deal as well. While the lower and farther that you are able to comfortably reach, the better in terms of aerodynamics, don't get stuck with handlebars in the wrong spot just because you're a girl.
Alternately, sit on the bike in your normal riding position while someone holds it steady. Without changing position, remove one hand from the bars and let it relax and dangle freely. Without stretching, rotate your arm in a large arc. As it comes back to the bar, if it comes ahead or behind your other hand, your handlebars need to be moved.
Allow us to fit you to a bike!