Dear friends,
To preface this piece let it be known that I ride about a 50cm c-t frame most of the time. I have owned LOTS of classic bikes my size and built over 30 for myself over the years. One thing I know. I know what I like and I know what works for me. I have conducted many experiments for the purposes of learning more and understanding what I experience. To be perfectly honest, I normally chuckle during many of these discussions where people are citing formulas and scienticic theories to explain or justify why a bike works or doesn't work. I have learned what I know from PERSONAL EXPERIENCE which means much more to me than every "system" and "philosophy" or "formula" I've ever encountered. Every one of the systems has exceptions to the "rules" that only experience can properly translate into a perfectly fit and useful bike frame. Small frames are particulary effected by these variations. Building a frame starting from a dimention (front center) that isn't directly related to the rider and intended use of the bike is backwards in my opinion. Wheelbase, bottom head angle, trail and other "resulting" dimentions should not be used as the standards; especially if the framebuilder actually knows how to design a frame that fits and performs to specifications, or better yet, beyond the expectations of the owner. That is my goal.
As far as I can tell, building to a front center is solely for the purpose of "creating" toe clip clearance. I can think of no other reason to start there. If someone else knows more about what else might be the purpose of starting with a front center standard, I'd be interested to hear it. I understand about "setback", but the bottom line is it still comes out as being a specific seat angle. Why not just determine the proper seat angle and be done with it. I have noticed that most of the builders who work to a front center tend to be building "semi-production" type frames as opposed to "true custom" frames by my deffinition. Also they tend to work from something other than a full scale drawing. What they may not know is that the drawing has numerous uses that tell the sensitive builder subtle things that the "OUIJA BOARD" systems cannot account for. Doesn't matter particularly unless one is really going completely custom from the ground up. To explain further would take a lot of time, but trust me this is true.
In order for a small frame to reach the front center dimention it is common to do several things. Increase seat angle, decrease head angle, add fork rake, and sometimes lengthen top tube and or raise BB height a bit. On a small frame I believe I cannot feel the difference between a BB height of 10 1/4" as opposed to 10 3/8", so I don't get too up tight about a slightly higher BB on a small frame. All of the other compromises DO have an adverse effect on how the bike fits or steeres to some degree or another. The steering suffers the most. For me this is unacceptable. I cannot stand the feel of bikes built that way for myself. It drives me nuts and really detracts from the pleasure of my cycling experiences. Perhaps others like that feel, but I can't imagine why. It is unneccessary and annoying in addition to being unstable by my deffinition (for those who like to redefine common terms they will call it the opposite of what it is).
Having over 30 years experinece with toe clip overlap I have to enlighten those who insist on eliminating it. For starters, as a true custom framebuilder one must discuss these matters at length with the customer. If the customer insists on compromises to accomplish clearance, I pass on them. I know they will find someone who will accomodate them. If it's an issue then 650c wheels are the perfect solution; if they can't go that route and trust my experience with these bikes, they're obviously in the wrong place. I don't try to accomodate that, I don't need to. The customer will suffer and most likely never know otherwise, so why worry. There are plenty of people who do come here for exactly the reason that I know what I'm doing and why.
The only time one even has to consider overlap is while making VERY sharp turns at under about 5mph. Exactly how much riding does one do like that? A little attention if starting up from a stop (like maybe make the bike go straight instead of sideways) and there is nothing to think about. Cycling is a potentially dangerous activity. One should be competent to ride a bike. It is a sophisticated piece of sports equiptment at this level anyway. Something as simple as that should not rob the bike of it's potential to perform to accomodate such a non-issue in my opinion. If you can't handle toe overlap of a reasonable amount you've got no chance against road hazards, cars, potholes, other Jabonies who can't handle a bike, and hundreds of other things. Does any of this make sense? It does to me. My personal experience has shown me that relatively speaking it is foolish to design a bike to meet a front center dimention. Just my opinion.
So what happens if you go the other route? Well, you start with the rider and the intended use for the bike. I'm not even going to try to explain how I go about determining what to build. It's all in my head and comes from experience. There is no formula. Every bike and every rider is different. Plugging numbers into a computer program never did it for me. You use that if you don't know how to think and reason for yourself and apply EVERYTHING you've ever learned about building frames in every single bike. Sorry if that offends the technical types. It's nothing personal, it's just the way I operate. Applied knowledge, period. No book forthcomming, for obvious reasons. I cannot pass what I know on. I will die with it, sorry.
I begin with the seat angle. Once I have established that I determine the top tube length/stem length combination. The actual frame size can vary a lot more than most people are willing to accept from my experience. Frame size has to do partially with position on the bike relative to several other factors in the design. As a custom builder, I don't just build racing style bikes. Bikes for different purposes can be different sizes for the same rider, but I find most people are too rigid in their belief of what "frame size" they take. The rest of the frame design isn't related to the ride as much, but have to do with weight distribution, fit, steering qualities, how the bike handles the gearing, etc., etc.. It's not rocket science really, but knowledge and common sense are very important. Otherwise you have to rely on formulas and whatnot. (There's that word again, what the hell is "whatnot" anyway?) I determine each of these dimentions based on the conditions the bike will face, the components, and whatever special needs the rider requires.
The resulting small frame designed this way is comfortable, steers beautifully, and rides and fits the rider the way it should. The pleasure of the experience is enhanced. Performance is enhanced and confidence in the machine is complete. I have and have owned a considerable number of Masis my size (built to front center standards) which are nice to own but not nearly as fun or as safe to ride in my opinion. I ask a lot of my bikes. The equivelent Colnago my size isn't as "valuable" or "desireable" as a collectable, but clearly outrides the Masis by a good amount. I even had the occassion once to have a bike that was dimentionally correct for me with the exception that it had a very shallow head angle and a lot of rake. I was going to get rid of the bike because riding it annoyed me so much. But during a repaint I decided to try to learn something. There was nothing I could easily do about the head angle, but I decided to remove the fork blades from the crown, unbend them from 5.2cm of rake to 3.8cm of rake just to see what would happen( knowing full well the result). I cut off the extra 6mm of length off of the forkblade that resulted from the straightening, and put the fork back together. Repaint the bike and get it back on the road. Immediately upon mounting her it was obvious that the "operation" was a success! I learned a lot from that experience. I still have the bike and it rides acceptably now. I'm very glad I resisted offing it. I would be kicking myself now and would have felt guilty passing it along to someone else knowing how it rode. Some people don't mind apparently, but it's a big issue with me.
I'm going to pause for now. I'm tired from the ride and tired of typing. I'll do part two a little later. I will recount what it is like to ride with my twin brother Joe Bell on a pair of old Colnagos during cold, heavy drizzle, fog, and lack of "training". Both of us are in love with our old bikes and I would like to tell everyone why.
Brian Baylis
La Mesa, CA
Typing is hard work!