Retul 3D Bike Fit – What’s all the fuss about?

Bike Science Derby’s Retul certified fitter Andy Brooke explains what sets Retul apart when it comes to bike fitting measurement systems…

We often get asked what makes Retul 3D fittings so special and I always answer with the same simple reply – accuracy and individuality! The system doesn’t apply a one-size-fits-all approach to fitting, it tailors the position to each individual rider based on their own pedalling style. That’s what really sets Retul apart from other systems.

Until recently riders were fit using very simple calculations for saddle height based solely on leg length, but this didn’t take into account how the rider pedalled. Lets take a simple example of two riders with exactly the same inside leg – one who pedals with their toe down and the other who pedals with their heel down. If you set both their saddle heights according to inside leg measurements then of course they’ll end up with the same saddle height. However, the rider who pedals heel down might be over-straightening their leg at the bottom of the pedal stroke and risking injury, while the rider who pedals with their toe pointing down might not be straightening enough and won’t be able to put the maximum power down. It really doesn’t matter which of these pedalling styles you use as long as you take it into account when setting your saddle height. Everybody is different and even the greatest cyclists in history have different pedalling styles from one to the next. Bike fitting has now realised that it’s OK to pedal differently to the Pro of your choice (because lets face it, s/he probably pedals differently to everyone they race against anyway!) so fitters have moved away from static fits based on leg length and towards dynamic fits – fitting riders on their bike to take into account their individual pedalling style. Before the Retul system, this relied on fitters working by eye but accuracy varied greatly between fitters and only elite level athletes could access the kind of motion capture technology required to accurately measure the angles of knees, hips and ankles during the pedal stroke.

This opened up another, cheaper option to get a dynamic bike fit – video capture. The main problem with video capture is accuracy. The lens in a camera, like the human eye, can shorten angles depending on it’s view point, making it incredibly difficult to take accurate measurements. Even if a camera can accurately show the pedal stroke, the next problem with measuring angles on the human body is setting the points to mark out the angles. With most video capture systems this relies on the fitter clicking a mouse on the exact pivot point within the joint. When the rider and bike are reduced on a computer screen from over 1.5m in real life to just 10cm, it’s very difficult to precisely find anything! Clicking just a few millimetres either side of the pivot point can change the angles recorded by as much as 5-10 degrees.

By placing infra-red LEDs on skeletal markers, the Retul system can ensure accuracy and repeatability and take the guess work out of fitting. Our fitters are still highly trained and the 3D motion capture technology we use certainly doesn’t do the job for us, but it does allow us to be confident in our recommendations and our measurements knowing that the figures we have in front of us are accurate to within a millimetre.

Retul is a 3D system. Three infra red cameras in the Retul scanner record side to side position and movement of each marker providing our fitters with with detailed information about how each rider sits and moves on the bike. No other bike fitting system gives this detailed insight. Side to side imbalances in pedal stroke can be spotted and corrected (either by direct interaction from the fitter or with flexibility work and strength training). In most cases our fit clients will leave us not only with a better bike position, but a suggested program of stretches and corrective strength exercises to improve their efficiency on the bike further.

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