Purely Custom fit bike

The dynamic fit bike

If you have been reading my earlier articles you will have seen references to the dynamic fit bike that I use.  So what on earth is a dynamic fit bike?  For starters a it rarely looks anything like a real bike.  Rather it’s a tool built specifically for the purpose of finding a rider’s winning position.

What is a dynamic fit bike?

The properties that define a dynamic fit bike (at least in my opinion) are the following:

  • It has a saddle, handlebars and pedals
    These are the ‘touch points’ of a bicycle, the relative location of which define a fit solution.  (The bottom bracket location and crank length are typically used to define the location of the pedals.)  Any dynamic fit bike worth its salt can facilitate quick and easy swap-out of all three touch points.
  • The saddle, handlebars and bottom bracket can be moved relative to each other
    This is the most important element.  It allows changes to be made whilst the cyclist continues to pedal.  With the vast majority of fit bikes, it is the saddle and handlebars that move.  There are versions where the saddle clamp is fixed and the handlebars and bottom bracket move, but that’s rare.
  • It has a controllable resistance unit
    The point of a dynamic fit bike is that it is, well, dynamic.  Movement is involved.  Not just movement of the touch points, but also the movements that a cyclist makes during the normal course of riding a bike.  For that to happen the pedals have to move.  There also needs to be something resisting the effort of the rider.  Aspects of a fit changes depending on the level of effort that a cyclist is applying.  For example, when a rider is working hard the weight resting on the saddle is lower than when they are cruising.  Hence it is important to check the fit at different levels of effort.  Of course it’s near impossible to exactly replicate the movement a cyclist experiences out on the road.  For example, getting a dynamic fit bike to sway as the rider pedals would be difficult given the mass involved.  This is why each full fit at Winning Position includes a follow-up appointment.  Sometimes a few tweaks are required after a few weeks to address issues that didn’t emerge during the fitting session.
Why use a dynamic fit bike?

A dynamic fit bike is not absolutely necessary to get a good fit – it is just very, very helpful. A dynamic fit bike:

  • saves time – the client doesn’t need to stop, get off and wait around whilst the saddle is moved or the stem is swapped out;
  • removes a number of limitations
    • because changes are so easy to make, the fitter is not tempted to limit the positions tested or just guess the ideal reach. To change the reach on a traditional bike by 5 millimetres the appropriate combination of stem (length and angle) and spacers needs to be calculated and then the changes made (assuming it’s even possible with the length of steerer and gear/brake cables available).  To make the same change on a fit bike takes just a turn of the wheel.  Or the spin of a drill;
    • the fit bike’s adjustable cranks mean that it’s easy to test different crank lengths – something that is not practical when using a bike on a trainer;
    • the fit is not constrained by the client’s existing bike. Wherever possible the fit should drive the bike set up, rather than the bike drive the fit;
    • in fact the client doesn’t even need to have a current bike so it’s perfect for those looking to buy a new bike;
  • results in precise measurements – taking precise, repeatable measurements on a bicycle is not easy, yet accurately recording the fit is essential to its implementation. The fit bike provides precise X Y coordinates that, with some maths, give millimetre perfect fit measurements.
Interest piqued?

Here at Winning Position I use a Purely Custom dynamic fit bike during all full bike fits.  If you want a truly dynamic fit, book in now to experience the difference a dynamic fit bike makes.