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Tuesday, June 26, 2012

Brush Strokes -- Designing and Fitting a Custom Bike

Building a bike, custom or not, is a lot like painting a picture.  You start with very broad, coarse strokes that don't really resemble the end product very much at all except in the broadest sense, and slowly those brush strokes get smaller, more careful and exact and, if you have a skilled painter, eventually you get a beautiful piece of art work.  Anyone can go through the steps, but not everyone has the skills gained from years of training and practice to do them well.

When it comes to painting, I suck.

I can go through the steps -- I can make broad brush strokes to begin with, and refine those to render a painting, but it looks terrible, because it's not something I've trained for or practiced.

In much the same way, anyone can go through the steps of bike fitting or custom bike design, but if they don't have the skills and/or the practice the outcome can be equally ugly.

Building a custom bike is even more tricky because, when done right it is a painting completed by two or more people.  The custom bike fabricators (machinists, welders, finishers, painters, etc) often don't see the rider first-hand.  The rider often just visits their local bike shop who is then supposed to communicate the fitting information to the fabricator.  The problem, and one I've seen a number of times, is that the local shop doesn't really know how to best fit their client, and the task of designing their bike is lost on them, so they leave much of the heavy lifting to the fabricator -- who has never seen the client.  This is when you get a custom bike that at best doesn't take full advantage of the possibilities of the custom build, and at worst (and more common than you think) actually doesn't fit any better than a stock bike off the shelf. 

I recently had a custom bike in the Studio, built elsewhere, in for a fitting and the very expensive titanium frame had the exact same dimensions as the clients previous Cannondale, because those were the dimensions that the shop sent to the custom fabricator.  Now there may be a situation where this would be the best geometry for a client, but that wasn't the case for this client.....that's why they were in to see me for a fitting.

The fitter needs to have the first and last word on the geometry of the bike as it pertains to the fit of the contact points for the rider.  This only makes sense since they are the ones actually seeing the client in the flesh.

In this same vein though, I will defer to the judgment of the fabricator when it comes to angle choices and axle (think about where the wheels end up) placement of the bike.  Good builders have an intimate understanding of the bike they're building -- how the material, tube selection, mitering, butting, welding etc will affect the ride -- and I think they're in the best position to decide if we need to, for instance, slacken a seat angle a quarter of a degree, lengthen/shorten a chainstay a few millimeters, or increase the rake of a fork to achieve a particular trail measurement.  I'm very happy to work with Seven Cycles on the majority of my custom bikes because they excel at this and still will listen to and defer to my opinion on some of these decisions if I can make a compelling case on behalf of my client.

So, on to the process:

1.  The first step is the most 'coarse', where we're determining contact points -- trying to find the most neutral fit position for the saddle and handlebars so that the location of each exists in the middle of an imaginary box.  The box represents the likely and possible alternate positions -- some higher, some lower, some further back, some further forward.  If we can design the frame and then the rest of the bike around these points, so that any point within the box is possible, then we'll have a very easy-to-fit bicycle.

2.  I can take these initial contact points and work backwards to find some of the basic frame dimensions -- I usually start with either effective top tube length and head tube length, or frame stack and reach.  I have some custom excel files I built years ago where I can plug in any combination of head angle, head tube length, stem length and rise, wheel diameter, headset type, headset spacers, seatpost heights, seatpost setbacks, seat angles, etc etc etc and it will give me the dimensions I need.

3.  This bare-bones information is sent to the builder for the first drawing and specs.  From these rudimentary measurements they can flesh out the finer details of the frameset -- the head and seat angles, amount of top tube slope, lengths of all tubes, and not to be forgotten, fork axle to crown, rake.  Another huge benefit of working with Seven is that they build their own custom raked fork in 3 millimeter increments.  Being able to control the position of the front axle is critical to translate the rider's custom positioning into the best possible weight distribution across the length of the bike.  Standard stock forks come in usually just 2 or 3 different rakes, which can severely hamper the handling of a bike.  Ask any of your very tall or very short friends who ride and you'll hear numerous stories about speed wobbles and poorly handling (especially downhill) because the forks for most stock bikes are designed for the middle sizes (53 - 57 cm), not the big and the small.

4.  Once we get the specs back from the builder I can review them with the client and explain what I'd like to change (if anything) and why.  Or I explain why I like the specs, and to the best that I can, I try to "show" the client how these specs will best suit their fit, riding style, and goals for this bike.  I may go back and forth with the builder a couple times until we end up with the specs we're looking for.

As I mentioned before, vetting the specs is critical, and should be the job of the fitter, not the builder since the fitter (me) is going to be the one working one-on-one with the client and the one ultimately responsible for their satisfaction.

5.  Next,  we sign off on specs and the builder begins fabricating the bike

6.  Get the frame, start building.  This is where choosing the correct components is key -- the right crank length, appropriate setback on the seatpost, making sure the length of the stem and the reach of the bars don't cause any problems with the overall reach of the bike that we're looking for. 

This is where I build the bike so that the bars and the saddle get set in the center of that imaginary box -- by properly designing the frame I should be able to get the position here with all the parts being set up "in the middle".  What I mean by this is the saddle is clamped in the middle of the rails by the seatpost, the stem is not overly long or short (maybe 105-110 mm) nor does it have a drastic rise or decline to it (+/- 10 degrees), there aren't a ridiculous amount of spacers under the stem (most carbon forks are limited to a maximum of 35-40 mm of spacers), etc.

If I can do this, then when we go on to the next step, the first fitting, we'll have lots of adjustability in all the settings.

7.  First fitting.  We'll be 90-95% done or more after this fitting.  This goes very smooth since we've done a lot of the heavy lifting before hand and eliminated lots of potential problems because of the way we designed the bike.  The adjustments we have to make are often very small -- a millimeter or two here and there -- precisely because we did plan meticulously ahead of time.

Of course, I still use the capabilities of the infrared system by Retul (every bike I build, custom or not, includes a full bike fit).

8.  Then the client needs to ride about a dozen times.  Often we need time on the bike to fully assess how certain changes will affect the rider.  Muscles and other soft tissues need time to adapt to the new lengths that they're working at. 

9.  Second fitting -- we'll be 98-99% after this fitting.  Because we need time riding to see how the body will adapt, I include follow ups for the first year in the cost of a new bike (and all my fittings for that matter) -- I don't want there to be a barrier, like having to fork out another $50 or more, for my clients checking in to make sure their fit is progressing as we expected.

When clients can't come in for a follow up -- I build quite a few custom bikes for people who drive or fly in from all over -- we're often far enough along into the process that the changes we'll make are known entities (meaning we're often very sure which direction, if any, we're going to have to change things), usually very small, and don't require equipment replacements, only modifications.

A raised seat by a few millimeters; a small tilt of a handlebar; a mild tweak of a cleat.  In the case of clients from out of state, we can often consult remotely (Skype for instance) and work through the change without any trouble.

So there's a lot that goes on in this process.  Sometimes the whole thing can take just a few weeks, other times it can take a few months.  And whether we're building a stock bike or a custom one, the end game is the same -- making sure we get the best fitting, best riding bike for the client.  And the only way we can do that is painstakingly making our brush strokes, one step at a time, until we end up with our masterpiece.


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