Many bike fitters get it exactly wrong by simply relying upon the precise measurements of their fitting systems and fitting guidelines from the manufacturer. Here are 3 reasons why they often get it wrong based on our case studies.
1. Saddle fit is ignored. You can place a rider in their ideal position for 5 minutes but will they stay there for 5 hours? This rider suffered from neck and shoulder pain. It’s easy to see on the left she is riding with straight & stiff arms and her shoulders are in her ears. However, the traditional fix, a shorter stem to reduce reach, won’t address the fundamental problem.
Her arms are straight and locked in order to rotate her hips and push herself up off the nose of her saddle, which is causing discomfort. This saddle pressure map shows how the majority of pressure is on the nose of the saddle.
In order to get the rider comfortable in a position they could sustain on the bike, we had to change the saddle and move the saddle forward. Again, traditional thinking is that moving the saddle forward will automatically move the rider’s position forward. If fact, many riders will actually move back on their saddle to keep the same position of their knee relative to the pedal spindle. In this case, we were able to get the rider comfortable on her saddle, and then the straight arms and hunched shoulders were eliminated.
2. Historic injuries. While measurements of leg lengths and flexibility may show a rider to be be symmetrical, those with historic injuries may sub-consciously compromise their position on the bike in order to protect the old problem. You can see in the upper diagram (a Wattbike power “polar chart”), this rider had significantly less power on the right pedal stroke than they did on the left, and there was an alarming dip in power part way through the down stroke on the right leg, which is the flattening of the curve between 1:00 and 2:00.
In order to diagnose this asymmetry in power output, we used the saddle pressure map to understand how the rider was sitting on their saddle. It turned out they were rotated anti-clockwise, and they had more pressure on the left side of the saddle.
Using a “shark” saddle, which forces the rider to sit straight on their saddle through the use of a “fin” at the back, we eliminated the dip in the power they generated with their right leg (see the lower Wattbike polar chart, above).
The rider was completely unaware they were not straight on the saddle and unaware they had a power asymmetry. They had, however, disclosed in the pre-fit discussion they had an historic injury of the right knee. Subconsciously, they had adjusted their position to “protect” that knee. They are now riding with a Shark saddle to ensure they are straight on the saddle, which addresses the dip in power, and they are working to strengthen the right leg to reduce the total power difference.
3. Your body changes,so your fit needs to change. Our bodies are wonderfully adaptable. We change in response to stimulus. For example, training that stresses our muscles results in the body adding mitochondria to supply energy to the muscles more efficiently. The body also increases capillary density to bring more blood to muscles, and we understand these changes as “getting fitter”.
Unfortunately, our bodies also adapt in negative ways. If you work at a desk 8 – 10 hours a day hunched over a computer, your body will adapt to that stimulus. So, a bike fit for a 50 year old office worker new to cycling should be VERY different to the fit for a 24 year old amateur racer working in a bike shop to support their racing habit. Where is the “average” between these two profiles?
If you have a bike fit when you are just starting serious cycling, that fit may no longer be correct for you after you’ve trained for six months. Your body has changed. You’ve gotten stronger, and the balance between your muscles has altered. For example, if your quads are stronger relative to your hamstrings than they were, then your ideal seat height may be different. Think of your bike fit as dynamic, not a one-off static event.