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Static Vs Dynamic Bike Fitting Systems

The art of Bike Fitting has come a long way in the past ten years. Back in 2007, bike fitting was almost unheard of a profession, but now it’s almost expected that a bike store will provide a fit with every new purchase, and bike fit studios are popping up all over the world. This growth has coincided with the rise of the Dynamic Bike Fit and a decrease in popularity of the traditional Static Bike Fit.

 

 

The Traditional Static Fit System

The conventional way to fit your bike was to obtain the inseam measurement (the length of a person’s leg from crotch to ankle), and a prescribed percentage of that number would be your seat height. The Lemond formula was: seat height = .883 * inseam.

The was a ubiquitous inseam measurer in bike stores; all new bike buyers were forced to straddle one of these contraptions and have it lifted up until it presses on your nether regions to get an accurate inseam. There was also a trend where the more advanced riders would have a higher percentage of the inseam. “Woah you’re at .94 – you must be Tour De France level!”

 

Do Static Bike Fits work? 

As there has been a boom in online sales of bikes, the static-fit calculators found on Canyon’s website – the ‘Perfect Position Systems’ – and elsewhere can be useful in choosing a frame size. However, once again, those calculators still have some shortcomings compared to the pre-purchase fit that will provide your ideal stack and reach numbers to allow you to choose a frame that is the perfect size for you. I see it as the biggest downside to Canyon’s terrific business model and growth. The stack and reach have become the primary methods of identifying a bike size, which is the length of the frame horizontally from the BB (bottom bracket) to the base of the headset, and the vertical distance of the same.

These metrics are not changeable, so it is essential to get a bike that fits your body type, flexibility and riding goals. For example, if you have a short torso and long legs, you’ll be wanting a bike with a higher stack and shorter reach. To prevent a bike arriving that isn’t quite right for you, the fool-proof method is to get a dynamic fit, and use the stack and reach tables to select the bike that is perfect for you.

 

Shortfalls of the Static Bike Fit System

A static fit system does not allow for any individual differences in the fit. What about differences in body shape (longer legs or small torso), or a rider’s flexibility or preferences for ankle position at the bottom of the pedal stroke? These wide ranges of individual differences are where the profession of bike fitting has risen. A good bike fit takes into account a broad range of variables which can only be uncovered through a complete history and physical assessment such as the following:

How flexible is the rider? Do they have tightness in their ITB or hamstrings? A long history or lumbar spine disc bulges, sciatic nerve issues or neck pain? Do they have a leg length or strength discrepancy? Also, what are their goals and abilities? What are their athletic backgrounds and bike-handling skills? What are their goals? Racing or touring? In Ironman do they want to qualify for Hawaii or finish before the cut-off? Once on the bike are they a toe-pointer or a heel-dropper? Does their knee trace straight over their mid-foot, or track to either side? How stable is their pelvis through the pedal stroke at varying heights?

 

“A good fit starts with the contact points – the cleats and saddle.”

 

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Only after we have taken into account all these variables can we begin to make decisions on cleat position, seat height and over-all fit specs. Once we have the right saddle height, we also need to work out the cockpit distance and saddle fore-aft, which also have some somewhat complicated formulas for the static bike fitter to work out, but are more accurately measured by a fitter taking into account all of the variables above.

 

The Rise of the Dynamic Bike Fit 

 

With the rise of the bike fitter as a profession, so has there been an increase in companies coming up with high tech methods of measuring and recording fit specs. Retül’s motion capture system was one of the first to market and dominated in the early days of bike fitting, and there are now many fit systems purportedly providing a fool-proof method of getting you your perfect fit.

Click here to read more about what goes into a professional bike fit. 

However, the very nature of the dynamic fit demands that at the end of the fit, only a collaborative effort from the fitter and the rider will decide the final set up, and no machine will ever be able to take over that role completely.

Bevan Colless

Author: Bevan Colless

Bevan Colless is a 18x Full Ironman finisher and 2 x Hawaii Ironman finisher who is a F.I.S.T certified bike fitter, Level 1 Triathlon Australia Coach, Physiotherapist, Sports Scientist and aerodynamic geek. Bevan is the Founder of Singapore Physio, which is part of the Asia Physio group, with 9 physiotherapy clinics in Japan, Singapore and Malaysia.

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