What’s the fuss about KOPS?

Knee over pedal spindle has had a lot of bad press over the last few years, but is there still value in the old dog yet? Lee Prescott, fitter and frame builder, thinks so.

KOPS, or Knee Over Pedal Spindle, as I’m sure you are well aware, refers to the practice of using the relationship between the knee (which part is also up for debate, depending on who you refer to) and the pedal axle, in order to determine saddle set back. Or so the myth goes.

But where did this come from? It’s pretty hard to define a clear source, but Fit Kit Systems from the 80-90s used it as part of its protocol, and there is mention of it in the CONI Cycling manual from 1972. It’s likely that it proliferated due to it being a simple measurement that anyone could take, with an inexpensive plumb bob, to get a cyclist pretty close to a decent saddle set back. I know that when I first started building frames in 1986 it was a pretty standard way of deciding on seat angle.

But this is all back when bike fitting was all just a practice of static measurements and conversion formula. The KOPS method became so endemic within the industry it became the de facto process. Dr Andy Pruitt uses it in his protocol described in his Medical Guide for Cyclists, and Phil Burt advocates its use – but only when taken dynamically – in his book, Bike Fit. But recently, KOPS has become something of a pariah within the industry, with some fitters suggesting that anyone using the method should be avoided.

Keith Bontrager was one of the first highprofile designers to cast aspersions on the use of static KOPS. His famous white paper discusses how the use of a static plumb bob measurement is too heavily influenced by gravity and becomes irrelevant as soon as the bike is on an incline. Part of his reasoning is that it has no biomechanical basis. Now it’s important here to remember that this was written before the advent of power meters or dynamic motion capture. Steve Hogg also wrote about how he was unconvinced by the KOPS method in his blog piece on Seat Set-back from 2011, pointing out that its more important to create a saddle set back that will unweight the torso. Both of these arguments are well worth a read and are widely available on the internet.

The thing that has struck me in writing this article is how little actual research has been done on proving what the true efficacy of KOPS is. My background is in industrial design and biomechanics/ergonomics, so I have a little insight into a similar field of investigation from another industry.

If you have a spare few moments, take a look into the biomechanics of ascending stairs; you will doubtless find hundreds if not thousands of commercially and academic funded studies. As a fundamental part of everyday life, a lot of time and effort has gone into designing the correct depth and amplitude of stairs.

When you look at studies of muscle utilisation whilst ascending stairs it may look remarkably familiar. Now I know they are not exactly the same, but use of the whole posterior and anterior chains are almost identical as that used when pedalling. So, with all this research where does that industry consider the ideal place of the knee when applying downward pressure? Take a guess!

That’s right. The typical description is of one of the landmarks of the knee to be over the transverse arch of the foot, in the direction of force. It’s that last bit that got me thinking. So, for the last two years, on all fits, we have been observing where the knee is in relationship to the cranks. Not as an academic study but just out of a commercial interest in improving our fit protocol.

We started measuring it on road bike positions by taking the average torque angle of the rider’s effort and then on the simultaneous video capture, graphing where a perpendicular line to the crank in this position would be. In all instances, once the saddle height was also optimised for the rider’s level of flexibility and torso angle, the knee lined up.

“Should KOPS be used to define saddle set back? Well, in isolation, of course not.”

We then started to follow the same process on TT and tri fits as well. Given that the saddle position on a fast bike is normally on the same radius as their road bike, but typically rotated forwards around the BB, we generally see average torque angles around 10 degrees or more further into the pedal stroke. Following the same process on all successful TT fits (the ones where the bike was capable of being adjusted correctly), we saw the same level of correlation.

So, what does that mean? I think we can all agree that using a plumb bob isn’t really relevant any more, but to totally dismiss the relationship between the position of the knee and the position of the foot would be cutting our nose off to spite our face.

Should KOPS be used to define saddle set back? Well, in isolation, of course not. And I think that is the most salient point: Bike fit isn’t a set of simple rules that if you work through you will come to a perfect position.

The biomechanics of the human body is a massively interconnected chain. As we will all have seen in our time fitting, a misalignment at one end can create a problem at the other. Any metric that can help to inform us as to the efficacy of the dynamic position we are working on should be welcomed.

Moving forwards, we will definitely add this metric to our toolbox. It may not be used all the time, but it has become useful alongside some of the other specialised measurements such as measuring wheel weight distribution, pulse oximetry, occlusion detachment etc. that we can use as and when they are needed.

lee@ibfi-certification.com