What is bike-fitting ?What we call bike-fitting is the "science" that consists in measuring someone's various dimensions (around ten measurements), in order to :
- Choosing a bike's best sizes for a given person
- Find the optimal settings on this bike
There are usually a bunch of sport firms that propose for (fortuned) bikers to afford such whim for amounts of money that reach at least a hundred Euros.
However, most people willing to fit their bike already own one, which reduces the amount of work at least by half. And, having a closer look, fitting a bike is not so complex, especially when we read that many factors do not need to be accurate, and depend on the biker's feeling and preferences.
Summarizing, there are 3 places where our body is in contact with the bike:
- The feet (pedals)
- The saddle
- The handlebar
Hence, four dimensions are essential:
- Saddle-handlebar distance
- Saddle-handlebar horizontal drop
- Saddle-crank distance (Saddle height)
- Saddle setback (horizontal delta with the crank)
Additionally, the optimal pedals radius can be deduced and calculated, despite MTB own the standard of 17.5cm.
Considering that most people choose the saddle's height by intuition, and the handlebar drop rather accordingly to their flexibility (as low as aerodynamics do not conflict with back pain), only the saddle setback and handlebar distance are really essential, and these two data tend to be neglected by most folks.
How to measure yourself ?Many websites propose user-friendly interfaces in order to calculate the bike's optimal parameters.
competitivecyclist.com is one of the most intuitive, and lots of clear videos explain how to perform all measurements.
If you are alone, a stool, a large book, and a rule and a pen are just what you need. For the arms length however, you may need a second person.
How to interprete the results
The website then calculates the bikes dimension. You may choose MTB, road bike, or time-trial (triathlon).
Note that each of them, except time-trial, you have different types of settings.
For the road bike, there is Eddie, French and Competitive. They vary between comfort and efficiency, with french being a compromise for long distances.
For MTB, there is XC, All Mountain or Enduro. Depending on what type of XC (cross country) you do, because many people have very different definitions, you may choose closer or less from that of road bike (the most you ride a flat terrain, the most you may adopt a position similar to road bike).
On competitivecyclist.com, not all bikes type show us all the data we need, so make the calculation for the 3 bikes types. Make sure the bike is on a perfectly horizontal ground.
- The saddle setback is measured with a rule and a plumb-line. This setting, shown only in time-trial, is taken from the nose of the saddle to the vertical line aligned with the crank axis. It usually varies proportionally to our inseam. The smallest is this distance, the most you will be efficient, but the less the position is comfortable as we are "pushed forward" as we pedal. Too long, we may feel like pulling the handlebar while pedaling, which is absolutely bad for the efficiency and the backbone. In MTB, a saddle setback tha allows adopting easily the downhill position out of the saddle is essential for a good bike handling.
- The distance of the saddle to the handlebar is measured from the nose of the saddle to the handlebar. The rule makes the job. Take it only after having a correct saddle setback. If the distance is too short or too long, you will have pain in the back. The idea is that your arms should support your bust vertically and therefore not tire it forward or backward. In MTB, the distance might be slightly longer as we pedal more often out of the saddle. The only way to change this distance, assuming we won't move the saddle, is to get a shorter or longer stem length.
In other words, the keyword of comfort is:
- arms should support your bust vertically and not slantwise to relieve your back.
- legs should push vertically compared to the center of gravity of your body (reason to be of the saddle setback)
- The distance from the crank to the sit is measured as well with a rule. Beware, the measurement is taken under the saddle as described the website. However, this measurement might not be very accurate as taking the inseam is not an easy task. If you feel this is incorrect, adjust the saddle height in order to have horizontal feet when the leg is stretched downside.
- The horizontal drop between the handlebar and the saddle is measured with the plumb-line again. As mentioned earlier, apart in time-trial where one fit only is optimal, this may vary accordingly to the biker's flexibility. Those who can't touch the ground with fingers while bending the body and standing on legs may need a smaller difference, while the real time-trial racers will get a significant drop.
Besides of this four essential settings, we can include a few more elements that go around the handlebar: handlebar type and width, horns (for MTB) and tri-bars (mostly for time trial but also road bike)
In mountain-biking, two types of handlebars are found: flat bars, and riser bars. Most often, flat bars are narrower, while riser bars are wider. The later is more and more popular, however both have advantages and inconvenients. It all depends on the terrain: the wider, the easiest is the bike-handling, but the narrowest, the best is the position for your back. Those who ride straight and flat pathes should prefer flat bars.
Another characteristic of riser bars is that they elevate the position of hands, and this axis near hands is to be taken in consideration during measurements, not the axis near the stem.
About MTB horns, here it also varies with your style of pedaling uphill: out of the saddle or not, and if yes how far: the further the longer. Horns should be oriented with the same pitch than the stem. Their goal is to switch the position of hands during uphills, in order to make them work like perpendicular side-pivots, which will relieve your hands.
Settings are far more complex than it seems when it comes about tribars, also called aero-bars, in road-cycling. Many data shoud be considered, at least eight dimensions: both the bars and the elbow pads, each in the three dimensions in the space plus their pitch. These data are provided by .. in the triathlon configuration, but above all you should always do few tries before you go for a long ride, the first tries are rarely perfect.
And then....Jump on your bike and go ;)
And don't forget to always take the adequate set of screwdrivers after new settings, you always find some improvements and may refine some settings.