Saturday, May 4, 2013

My trip to 3D Bike Fit

A month ago I went to 3D Bike Fit. I've known Kevin Bailey for a long time, as well as Alex his partner, back to their days with Bike Nüt in San Francisco. I procrastinated, though, since I'd experimented with fit a long time and I'd been to several professional fitters and didn't think the time investment would be worth it. My schedule most days is super-busy and if I do one thing something else doesn't get done.

The problem I have had with most bike fits is they seem strongly biased. I go in, my present fit is assessed, a few tweaks are made, and out I go. This seems strongly biased. Ideally the final fit shouldn't depend on the initial fit. If there's an optimal fit, why should it matter what I've been riding? It's like if I ask you to solve the equation 3x + 6 = 21. There's only one answer with conventional numbers and it's 5 (corrected!). Whether I start with an initial guess of 2 or an initial guess of 42 is irrelevant: I've got to end up at 3.

Unfortunately bike fitting isn't that simple. There's a range of solutions for a given physiology. So from that perspective, it makes sense to deviate as little as possible from an initial rider fit. Additionally, there's different philosophies on how to trade off different elements of fit. If I'm riding Amsterdam bike paths to and from the market, I'm certainly not going to want the same fit as a track sprinter. Additionally a track sprinter wouldn't want the same fit as a road racer, a road racer the same fit as someone doing double centuries, a double century rider the same fit as someone riding 1200 km brevets. There's trade-offs between aerodynamics, comfort, power, and acceleration.

But the biggest challenge in bike fit is that bikes are not designed for fit optimization. For example, if I pivot my body forward about the bottom braket, rotating everything forward, modeling has shown this has little effect on pedaling efficiency. Yet to do this on a bike requires making enormous changes: saddle up, saddle forward, handlebars lower, handlebars rotated forward, stem longer. If I were to optimize any of these components individually, I might well assume that changing it would result in an inferior fit, but only when changing them in coordination would I be able to investigate the effect of rotating the body about the bottom bracket. It's possible, for example, that doing so would result in a superior distribution of weight between the front and rear wheel, or perhaps a more balanced transition going from seated to standing. This would be easy to investigate with a specially designed fit bike, but it would be time prohibitive to investigate on a conventional bike,

Kevin @ 3D Bike Fit begins with a physiological check. In my case this included flexibility, how I stand, how I sit. My flexibility is relatively good but I have points of weakness. And he observed something I don't recall being observed before: that my left arch was collapsing. This results in a functional leg length difference, he pointed out. When the arch collapses that lowers the leg, and that lowering of the leg requires a compensating pivot in the hip. One approach to this might be a shim in the cleat, but a better approach is to support the arch in the left shoe. My Sidis had seen enough miles, and he strongly recommended the Specialized S-Works shoes with a dual-boa adjustment. These were remarkably comfortable at first, although perhaps slightly confining in the toes. The shoes have a built-in varus adjustment, he said, which I needed on my left side but not my right. He later neutralized the right varus adjustment with a shim Specialized makes for the purpose. He also gave me heat-moldable footbeds which provided a really firm feeling in the shoes. It was a feeling of connectedness I hadn't felt since I had Rocket 7's over ten years ago.

But it's hard to evaluate shoes in the hurried environment of a bike fit. The shoes are indeed comfortable, except for two features. One is the toe area. As I noted, my toes were somewhat confined, and the shim in the right shoe made them even more so. Extended riding resulted in the feeling the knuckles in my right foot abrading against the mesh on the top of the shoe, in particular at the location of a seam near the toes. On the left side, I had a very strange experience of some padding on the low-cut ankle rubbing against a nerve. I'm not sure why this didn't happen on the right side, which was fine. This was excruciating. The first ride I did I was convinced I'd ripped my angle to a bloody pulp. But after the ride, there was no visible trauma. I tried shimming various objects there to diffuse the pressure point. A coffee cozy picked up from the trash at a cafe helped a lot. Best of all was a credit-card-like object. That worked great and seemed fairly stable if placed correctly. This "solution" got me through Devil Mountain Double. For the right shoe, I eventually removed the varus adjustment neutralization shim. This gave me back just enough room in my toes that I was comfortable. This is acceptable, but I really need to figure out how to deal with that left ankle problem. I tried padding the shoe out with moleskin near the painful contact point. This didn't work as well as I'd hoped. At some point it risks replacing one problem with another. I also contemplated cutting away the portion of the shoe causing the issue. But the heel is already quite low there and I worry it might cause other problems.

On the pedal side Kevin likes the stable platform of Shimano SPD-SL pedals and cleats. These are indeed stable: once my shoe is clipped in it feels solid, and I don't find myself fighting against the lack of float. Another asset to these shoes is the cleats can be set up with a narrow stance, which he determined I needed. The video evidence was there: each time he made a change my pedal stroke improved. But what I don't like about the pedals is the difficulty clipping in. Usually a few seconds lost stumbling with a single-sided pedal is no big deal. However occasionally it is. For example, when clipping in at the start of a hillclimb every second lost is lost: you can only climb a hill so fast and unless drafting has a large influence, for example on a relatively flat section of road, then if it takes longer to get going it's going to take longer to get finishing. Even at Devil Mountain Double the clip-in problem may have been an issue if a delay clipping in caused me to subsequently just miss a traffic light. So I don't like the slow clip-in and that alone is reason to dislike these pedals, even if I like many other aspects. They are heavy but the cleat is light and the combination isn't that bad, although I've not carefully measured it since I've been more focused on the functional aspect.

The coolest thing, however, was the position tracking. Kevin attached markers to key pivot points on both sides of my body. The Retul system, as I understand it, uses a rastering laser which converts position into time, so based on when it sees reflections from the markers it determines the position of each marker. This allows him to track my body position, not only for video recording, but also for the automated real-time extraction of key parameters like joint angle. The traditional approach for joint angles is either goniometers, which can only be done statically, or using video analysis software like Dartfish, which is subject to perspective distortion. But Kevin improved on the Retul standard by building a rotating platform to allow for the sequential measurement of the left and right sides. This assumes you pedal the same during the two orientations, ideal would be simultaneous measurements of the multiple sides, but this is probably a good assumption and the solution is brilliantly done.

The fit took hours... close to four, I recall, and Kevin constantly complained about how it was a rush job. Yet this blew away prior fits I've had.

But there a few issues. One was saddle height: he set saddle height using a 35 degree bend angle in the knee as a target. I've read a bunch of papers and book references on the subject, this put my saddle lower than, or at the low range of, all of them. This is not itself an issue, it doesn't mean the fit was bad. But since I felt I had more top-end power with the seat higher, I felt I had license to act on that, and I raised it 1 cm. This wasn't as high as I had it prior, but seat height doesn't exist in isolation, and with the other changes he made my original seat height would have been too high.

The other issue was a source of some tension as I expressed reluctance to switch to shallow drop bars. A reason for this was I didn't like the specific bars he had: I don't like the raised center section of 31.8 mm bars (I use 26.0 mm) and I didn't like the heavier weight of what he had available (I use a humble Ritchey Pro bar and a Performance Forte stem, a combination which combined with some relatively cheap after-market Ti bolts yields a remarkably light package). But in the end I didn't see the need. The motivation for compact bars is to keep the back angle the same when transitioning the arms from the hoods to the drops. But why would I want that? The whole point of being on the drops is to get lower, for example for descending or due to high-intensity riding which can't be sustained for more than, for example, 10 minutes. While for the hoods I want to be able to open up a bit, relax a little, either for climbing when wind resistance is less important, or because I'm in a pack and wind resistance is substantially reduced and I want to have the option of straightening my arms and improving my view. I am a big fan of riding with bent arms: it absorbs shock and promotes relaxation, providing room to move by straightening them without impeding the ability to get aero when necessary. But that doesn't mean I want my drops raised up to such a height that they no longer expand my position options.

Anyway, he did the best he could, he said, with my present bars, rotating them forward (I'd had a prominent upslope on the drops to provide a more comfortable position on the ramps), raising the hoods, and raising the bars as high as my stem and steerer tube would allow. This really was an improvement, and I eventually converted my Ritchey Breakaway, my second-tier road bike, to a similar position. I find I can still get as low as my physiology allows without my knees pounding against my chest, an impact which obviously wastes energy, but I am more comfortable in the drops on extended descents, where they provide better control than descending on the hoods.

Indeed, on Devil Mountain Double, not counting some minor foot issues, I was remarkably comfortable for the 13+ hours I was moving. And this is after I raised my saddle, as I noted.

One thing I didn't see was an explicit power increase. My times up Camino Alto (a 4.5 - 5 minute climb) aren't noticeably faster and when I started doing sprints with a power meter, my sprint power was 100 watts lower than it had been last August. I've since gotten my sprint power back close to where it was then (although my best sprints were on my Ritchey Breakaway, which still has Speedplay pedals, which I rode with my Bont shoes, although other aspects of the fit I transferred to that bike). But there was no magic power boost, in the short term, fromt he position change. But a lot goes into power and staying fresher through a long ride is more important than peak power over intervals when fresh.

So it was a very positive experience and I strongly recommend 3D Bike Fit to riders who are serious about optimizing their positions.


Robert said...

I think x=5.

djconnel said...

Funny! I fixed it.

specialist said...

Clipping into spd-sl's is pretty quick when you get used to them.