Perhaps the most important consideration about the act of cycling is that of bike fit. So much so, that a whole industry has grown up to address the issue…
While everyone would agree that getting your contact points in the best places in order for you to pedal efficiently, with some modicum of comfort, is of major importance; so much so that it could be the most important determining factor when it comes to your personal velocipede. The consequences of putting your pieces parts where they go on any specific bike is often times glossed over…
With the advent of the compact frame, and T-shirt sizing, which the Inner Ring’s article The Ancestor of Your Bike states as having occurred more or less for reasons of profit, more people are being fitted to fewer frame sizes…
People, come in all shapes and sizes, the range of which can be rather amazing. This holds for those of the professional ranks as well (see Anthropometrically Speaking). The bicycle industry has done a remarkable job of getting everyone’s contact points where they ought to be on the fewer sizes offered, even to the point of getting those who ride professionally (who used to be the most demanding of a custom fit…) into the fold…
It would seem all is right with the world, and the pelotonese shall rejoice…
Is it truly a matter of one, or six, sizes fits all?
Coming from a motorcycling background, I can say that weight distribution has a huge effect on the way a motorcycle behaves. Yet, in comparison, the rider is a smaller portion of the total mass, and he/she has much less affect on the center of gravity of the motorcycle/rider system than does the cyclist on the bicycle/rider system…
In order to keep this article somewhat succinct (that’s likely…), I would point you to this article on Bicycle and Motorcycle Dynamics as a primer on how all of this works…
In motocross, the bikes being ~200 lb give or take, the rider is more or less about 50% of the mass. Without the ability to move about the bike, I can say with certainty that it would be nearly impossible traverse the given terrain and not fall off, even with the freedom of movement it takes considerable doing to remain aboard, the proof of which I have experienced first hand… frequently…
On pavement, weight distribution is of no less importance, and the rider’s ability to influence it much reduced. Road motorcycles tend to be heavier than their off road brethren, and there tends to be much less standing and moving about, the rider’s position is much more static…
In trying to fettle a road going motorcycle to optimize its performance, the weight distribution is altered subtly by adjusting the front and rear ride heights, as well as the suspension to optimize their compression and rebound movements, which have a dynamic effect on the weight distribution. This determines the motorcycle’s ability to provide the necessary feedback to the rider, so that he may pilot it in such a manner as to benefit from riding near as possible to the limits of traction…
Upon initial construction of a bicycle frame, the builder, or designer, has nearly unlimited freedom to put the center of gravity wherever it need be, and thereby establish the weight distribution. Unlike motorcycles, there is precious little that must fit within the confines of the frame, and the greatest influence on the center of gravity is mounted outside the perimeter of the frame…
Once a frame is constructed, and within the constraints of any particular cyclist’s fit parameters, there is precious little if anything that can be done to change the center of gravity…
We’ve all seen bikes that were set up in a manner to facilitate their riders fit parameters that look all jacked up, faster backwards, or how ever you want to describe it; and the Giant pictured in the Inner Ring article is a perfect example, though no where near as severe as I’ve witnessed…
So what? Ya gotta do what ya gotta do…
Unfortunately, there are consequences of this, and they usually rear their ugly head at the worst possible moment. While nearly any setup can be ridden at a moderate pace under ‘normal’ conditions, that doesn’t mean it will work descending off a mountain at speed…
My dad is a perfect example. He’d been riding his Slim Chance for years in Florida, but, he had some neck problems and raised the handle bars up to seat level or maybe a little higher. The combination of the height plus the angled up stem causing the extension to be shorter, putting him both higher and further back, position wise, than he had been before…
He rode the bike that way for quite a while, and then when he came up to ride in the mountains, low and behold, he got a speed wobble on a descent that nearly scared him to death…
My dad is about 6 feet tall, and the Slim Chance was something on the order of 57x57cm with 73deg parallel seat and head angles. Pretty normal stuff, and previously, with a 110 – 120mm stem the bike seemed to work well for him…
By taking all of the drop out of the handlebar setup, and shortening the effective stem extension considerably, he changed the weight distribution, moving the center of gravity rearward and up, un-weighting the front wheel, and causing the speed wobble…
He never suspected he had a problem until he came up here, and the problem occurred…
It’s not enough that you can put parts on a frame, and with some adjustments have your contact points in the right places…
The contact points have to be correct and, as Richard Sachs says, the wheels have to be in the right places…
It doesn’t matter how the frame tubes are oriented, or what they’re made out of, but those two criteria have to be met…
If you can do that with a small, medium, large, or x-large, then the world is your oyster…
If not, consider that the possibility exists that the bike may exhibit unsavory handling traits in some portion of its performance envelope…
This is tricky, it’s difficult if not impossible to know what you don’t know, but with the price of bikes these days, it’s probably worth it to spend some money with a reputable, experienced fitter or bike designer type person so that you don’t make a costly mistake…
You can have a bike that fits and handles properly, you just may not be able to find it in the current production sizing scheme…
