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Man vs machine: Inside contemporary bike fitting

James Spender
14 Sep 2016

From wireless fit-bikes to pressure map saddles, the face of bike fitting is changing fast. But are we right to ditch the tape measure?

‘If you ask me, Merckx was a tortured soul,’ says Phil Cavell, founder and co-director at London-based bike-fitters, Cyclefit. ‘He was never the same after his accident in 1969, and I think as a result his career ended abruptly.’

Cavell is referring to the high-speed crash at a motor-paced event in the Blois Velodrome, which claimed the life of Merckx’s derny driver, Fernand Wambst, and left the great champion with a cracked vertebrae and twisted pelvis. These injuries dogged the rest of Merckx’s career, and to Cavell’s mind turned The Cannibal from a hardy macro-absorber (able to just get on a bike and ride without complaint) to an anxious micro-adjuster ‘like the princess and the pea, even known to make saddle height changes during a race’. 

‘Look at Merckx through revisionist history and there’s so much you could have done. A really good bike fit and Merckx would
have been fine,’ he adds.

So what, in this day and age, constitutes ‘a really good bike fit’? And, moreover, how can you ensure you’re getting a good one? Perhaps
the latest bike-fitting technology has the answers… 

Rise of the machines

Many of today’s bike shops bear little resemblance to their forebears, particularly those that offer bike fitting. In fact, the very idea of a shop that is fitter first, seller of bikes second would have seemed alien 10 or 15 years ago. 

Andy Sexton, founder and head fitter at Bike Science, says, ‘There are still a lot of traditional shops where the customer walks in and the old bloke behind the counter looks them up and down and says, “Oh yes, you look like a 56cm to me.” But the days of shops being able to get away with that are numbered. From the customer’s point of view, especially now considering the average price of a bike, they’re going to demand a higher level of service than that. That’s why they come to people like us, because while we sell bikes, we’re fitters rather than a shop.’

So what would you expect to find in a shop like Cyclefit or Bike Science? Or rather, a studio, as has become the favoured term to describe a serious bike fitter’s practice. Well, for starters the most conspicuous piece of equipment is likely to be a fit-bike, on which the rider sits and pedals while the fitter makes adjustments. 

‘Essentially a fit-bike is a giant X-Y tool,’ says Cavell. ‘So we’re not thinking about stem length, top tube length and seat angle, but rather points in space on a theoretical X and Y grid. We use the fit-bike to ascertain the X-Y coordinates of the handlebars and saddle in relation to the bottom bracket, and use that data to inform the set-up of an actual bike.’

While the precise nature of each fit-bike differs, the principles behind them are united: observe the rider riding, take measurements and be able to make adjustments on the fly. 

‘Bike fit evolved from the godfathers Andy Pruitt [now heading up Specialized’s BG Fit programme] and Phil Burt [lead physio at British Cycling],’ says Bespoke’s head fitter and ex-GB track cyclist Ben Hallam. ‘These guys started off with goniometers – effectively great big protractors. They’d stop you at the bottom pedal stroke, then place the goniometer at the middle of the knee and measure the angle. The disadvantage is that when you stop during a pedal stroke there’s a tendency to drop your heel slightly, which then straightens your knee, or point your toe, which bends your knee – both of which change the angle. So it’s hard to take truly representative measurements during static fits.’

The answer, then, is to perform a dynamic fit, where rider measurements can be collected during pedalling. To do this, the latest bike-fit set-ups now employ motion capture, where a computer maps out and records those measurements for the fitter based on lines manually superimposed over video footage or from sensors stuck to the rider’s body.

As with the fit-bikes, there are a host of different measuring systems available, but two of the most prevalent are from Swiss-based Dartfish, whose system has applications across a variety of sports, and Retül, a bike specific system developed in the US by Todd Carver and colleagues Cliff Simms and Franco Vatterott.

‘I’m a trained physiologist and I got my first job working with Andy Pruitt at the Boulder Center for Sports Medicine running the biomechanics lab, and that’s where I learned the use of motion capture,’ says Carver. ‘I teamed up with Cliff and Franco and in 2007 we launched the Retül fit system. It was the first of its kind. Up until then motion capture was expensive and you needed a PhD in biomechanics to do it, so we decided to create an affordable application for the retail level where the fitter didn’t need to learn so much about the technical aspects of it – they could just hit run, hit save and they’d get accurate data.’

The Retül system uses infrared LEDs stuck to the necessary joints and areas of a rider’s body, which are then ‘filmed’ by a camera and tracked in the corresponding software to produce real-time measurements as the rider pedals. The software itself has a database of normative ranges that Carver and his associates have built up over years of bike-fitting. The result is a system that can effectively ‘tell’ the bike fitter when they’ve got the rider’s set-up in the right ballpark. But Carver is at pains to point out that this is merely just useful data for the fitter, not a final solution. 

‘There are different ranges for different riders,’ he says. ‘Basically we’re trying to categorise professional, competitive and recreational riders. The ranges are a mean score across our riders of any certain type plus or minus one standard deviation. So within the pro ranks we took four World Tour teams and recorded all their positions. Their average knee extension is 36° and the standard deviation is 3°. So that’s what our normative range is for a pro roadie, which is useful for setting, say, saddle height. But this kind of thing is a point of contention because we also realise there are certain reasons why riders won’t be in a normative range. You’re trying to get their knee angle on a 36° plus or minus 3° and it’s just not happening – every time you raise their saddle they point their toes down, and it’s maybe because they’re guarding something like a tight hamstring. So the normative data is just that – it’s not suggested ranges, it’s just what’s normal. Having established that, we can teach fitters about normative ranges and when to vary from those for certain riders. It’s therefore key to assess riders for flexibility and strength before they go on the bike; only then will you know why they’re not in a normative range and be able to judge the fit accordingly.’

Redundancy package

Retül is a rather neat system – so neat that Specialized purchased it in 2012 to form the cornerstone of its BG Fit programme. But its abilities don’t end with just spitting out a few choice measurements from the motion capture. Thanks to a huge database of current bikes and geometries in Retül’s FrameFinder software, the system can go on to suggest bicycles – right down to choosing the correct stem length – that would suit the rider’s set-up. 

While that might sound rather too futuristic, Retül is not the only all-encompassing system. Guru, which was purchased by Dorel Industries, owner of Cannondale, last year, works in a very similar way, only adding in another extra step that on paper might sound like it could all but do away with the fitter. 

Using the 3D Kinect camera from Microsoft’s Xbox One console, the Guru system scans a rider’s body to determine his or her dimensions (shoulder width, inseam, torso length, etc) then automatically adjusts its servo controlled fit-bike to within the corresponding normative ranges for the rider’s dimensions. And this all before the rider has even set cleat on the fit-bike. The fitter can then fine-tune the set-up before Guru churns out a list of suitable bikes to choose from. Furthermore, while other manual adjust fit-bikes require one adjustment to be made before another can be – ie, change the fore/aft of the saddle then raise the bar height – Guru can make several adjustments at once. Thus it’s able to change a seat tube angle while preserving the stack height and reach of the overall set-up (whereas in a manual system altering the effective seat tube angle by moving the saddle backwards would stretch out the rider, thereby altering the reach and drastically changing the overall fit). The final feather in the cap of the Guru system is that the whole fit-bike can incline and decline to simulate riding up and down hills.

At this point it all starts getting rather technical, and many of the whys and wherefores that govern the merits of such systems come down to things like their usability and affordability – neither of which should be a concern for you, the customer. After all, you’re paying someone else to worry about loan repayments and how to operate the thing. But what should be a concern is: do you really need any of it? And moreover, just because your local bike fitter has a Guru or Retül setup (or a Shimano, Giant, Trek or any other for that matter, the list goes on…) are you guaranteed a good bike fit?

Keeping it simple

Many fitters still remain unfazed by the razzle-dazzle chutzpah of this latest technology, and one such case in point is Scherrit Knoesen, aka
the Bike Whisperer. ‘My view is that there’s an excessive enthusiasm about looking at bike fit technology, but if you care about fitting you should be looking at the person and what they want,’ says Knoesen. ‘I think the role of technology is providing the fitter, as an intelligent diagnostician, with the information he or she needs to make decisions. Take Retül – it says the knee angle is 35° and the right knee is wavering a bit. But the question after that is, so what? If the rider is riding 100 miles and that’s all they want to do and they’re not in discomfort, the answer might be do nothing.

‘Perhaps then we might be considered relatively low-tech; I use rulers, spirit levels, plumb bobs. But above all I’m using my eyes and my experience. I do use video and photography, but it’s mostly to help the rider see what I’m seeing; I can function well without it,’ he adds.

While in the face of all the latest gadgetry this might sound like a Luddite’s approach, other industry stalwarts back Knoesen up. 

Having been widely credited as the godfather, propagator and curator of modern bike fitting, Andy Pruitt is in a unique position to provide the final word. Previously the head of US Cycling’s sports medicine programme and now the director of the Boulder Center for Sports Medicine – as well as looking after the Specialized BG Fit programme – Pruitt has literally been there, seen it and fitted it twice. So how does he see the state of play in the bike-fitting profession?

‘I have a day job in medicine so I always use medical analogies. Take a surgeon. He might have better microscopes now, robotic arms to make bone cuts, endoscopic cameras. All his tools have improved, but they’re nothing without him to operate them. The same thing can be said of bike fitting. There are a couple of companies trying to bypass the fitter, eliminate them using technology and bell-shaped curve averages to fit people. But all that is just fancy sizing. There’s a big difference between sizing and fitting. If you eliminate the well trained fitter, you let technology drive it, and that’s where people get into trouble.

‘When a patient comes to see me with knee or back pain or whatever associated with cycling and they say, “I had a Retül fit,” and I say, “Who did it?” and they say, “I don’t know. It was a Retül fit,” that tells me that the technician was a very small piece of what they went through, and that the fitter let the technology drive the fit through the normative values. I don’t care how they bill it, how they sell it, that’s not fitting. That’s the use of technology by inexperienced people.

‘Technology in the right hands is absolutely the way to go, but it has to be in the right hands. Training and experience is the key. Bike fitting is all about the fitter. They are still, and will always be, the most important tool.’

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