Words of warning: I am writing this as much more my benefit insofar as "thinking out loud" helps me to process information. Several weeks of riding through back pain and frustration with budgetary concerns have resulted in my birthing this ridiculous collection of words. You're probably not going to read the whole thing, but if you share my obsession with getting the most out of a bike riding experience and my sense of frugality, you'll appreciate it.
I used www.BikeGeo.net to overlay the geometry of some bikes I have owned. This is a great tool for visualizing differences in bike geometry to help you imagine how one bike will be different from another. I am using my previous frame, a Soma Juice for comparison because, while it left some things to be desired in the handling department, my back didn't ache after riding it for several hours. To clarify, I doubt that the new frame caused my back pain, the new setup merely exposed an imbalance in my body that manifested as a back ache.
This frame is subtly but profoundly different from my old frame, or so it seems. For example, my previous frame has a slacker 72° seat tube angle and a 16mm offset seatpost, but my new frame has a 74° seat tube angle and came with an inline seatpost. This means that the resulting position of my saddle (saddle setback) is quite a bit forward of my previous saddle position, relative to the center of the cranks. A little basic trig will illustrate that on paper, but I was able to measure it as well.
In order to set up the bike so I don't look like tricycling circus bear on it, I had to put an offset seatpost on a bike that was designed with a super-short chainstay, which puts my center of gravity pretty far over the rear wheel -- a good thing or a bad thing depending on how and where you ride.
Conventional wisdom tells me to put my saddle back to the same position where I had it before, which I measured with the nose of the saddle at 75mm behind the BB on my old Juice. That's quite a lot of setback, and I don't have particularly long legs or disproportionately long femurs, to the best of my knowledge.
To achieve this position, I would need to get a seatpost with what I think is an unreasonable amount of offset and has very few options. in addition, I the resulting position would put my center of gravity waaaaay over the back wheel, resulting in terrific rear tire traction but no control over the amount of traction I get on the front, especially when climbing.
More importantly, it may be further exaggerating issues I have had with putting too much stacked weight on my lower back. If I keep going down that road, I will have relegated myself to riding a beach cruiser slowly down a paved path, which would be fine if I were closer to a century old.
Conventional wisdom also tells me to put my handlebar at the same height and distance from my saddle where I had it on my previous bike, assuming that the previous position was a good one. I have nearly achieved that and I am not particularly chuffed with the results. But was it a "good position" in the first place?
I had to take a step back and challenge the premise -- what is the optimal saddle offset for me? What's the best amount of reach and rise for my hands? Was the old setup optimal, or was it accommodating my body's imbalances and thus encouraging them to get worse?
If I could directly translate the old frame's dimensions to the new frame, should I? Time to re-think the whole thing. New bike, new fit!
Confronting Superstitions
A lot of bike fit advice relies on lore that is repeated enough to create memetic inertia. There are weird "rules" like the 40-60 weight distribution guideline, the "elbow on the saddle, middle finger to the middle of the stem" idea, goniometer measurements on hip, knee, and arm angles, and the eyeball-the-front-hub-through-the-handlebar theory, and KOPS or knee-over-pedal-spindle method of determining saddle fore-aft position, which Keith Bontrager calls KOPS a "myth."Additionally, I feel that most of the bike fit advice accumulated over the years have been more appropriate for road bikes and old school mountain bikes (many of which were essentially road bike with fat tires). All of these ideas have good intentions, but vague results from one rider to another and among bicycle geometries as they evolve for riding conditions.
Why so complicated?
As I was typing all this up, I started thinking: why is setting up a bicycle so complex? All I want to do it take a bike that is designed to fit a rider my size and set it up so I can ride comfortably and with confidence for a few hours at a time, so why am I considering advice on the internet that involves employing lasers, video motion capture software, a stationary trainer, and enormous protractors like you see in those fancy bike fit studios? What made this "necessary," and what do I hope to gain by moving my bike parts around by mere millimeters in one direction or another?
Unless a rider happens to be Vitruvian Man, any amount of calculations and measurements is only going to get within a ballpark of a good fit. After the pain and frustration of my last few rides, though, I am gun-shy about riding my bike at all. Until I get my body and my bike fit sorted, is riding worth the physical pain and frustration that result? This analysis paralysis might be worse than any amount of injury I could receive from riding an ill-fitting bike.This is where I quit crunching numbers and moved on to practical matters. I could stare at these numbers all day but nothing is going to substitute for placing my butt in the saddle and considering how the bike fits and handles. Unfortunately, none of the frames I am interested in riding come in a complete bike format to test ride, test rides in parking lots are no substitute for riding on the trail, and manufacturer demo days are few and far between.
I can conclude that the best way for me to fit a bike is to ride the bike mindfully, listen to my body, adjust what doesn't work to something that does work, and ride some more. That requires some knowledge of how my body propels a bike and what adjustments will change how that happens, which is the kind of knowledge I am seeking.
One thing that I have discovered is a better way to look at how a bike fits from a geometric standpoint. I start by dividing my fit into two dimensions based on the idea that all motions on the bicycle start at the feet: pedaling and wrangling.
By pedaling, I mean propulsion generated by the position of the bottom half of your body relative to the pedals. This means saddle height, saddle-bottom bracket offset, saddle angle and so forth. You can tell, within a reasonable margin of error, if a bike will fit you from a pedaling standpoint based on the seat tube length, seat tube angle, and effective top tube or ETT. Getting a solid pedaling position on the bike is essential for just getting around and should not be ignored, even on a mountain bike that is ridden in a variety of positions. This should be pretty straightforward, but of course, it's not.
By wrangling, I mean where and how your weight is distributed when you ride the bike actively based on your position of your hands relative to the pedals. This circumvents the saddle position because riding a bicycle is a dynamic activity, especially on a mountain bike.
When wrangling a mountain bike over the terrain, the rider is constantly changing the center of gravity to maintain balance and traction while vaulting up ledges, whipping around corners, or bounding down descents. The rider engaged in wrangling the bike is rarely seated, and increasing numbers of riders are using telescopic seatposts (including myself, hopefully, in the near future).
Solid numbers
Yet I still feel the urge to quantify everything, so I am working on learning what matters when it comes to fitting a bike, and what is coincidental. My goal is to record the relevant measurements and make subtle changes so I can look back and remember where I have been on this journey. For the slightly-longer term, I would like to be able to find what I am looking for and make an informed purchase on my next frame, be it a more svelt off-the-peg frame or getting something built just for me.
In bicycle geometry, I find that quantified as stack and reach are more relevant in understanding how the bike will be wrangled, whereas effective top tube better defines the seated pedaling position that you can achieve by moving the saddle position around.
Stack and reach have been defined as the plumb-vertical distance from the bottom bracket to the intersection of a horizontal line that crosses the top of the head tube (stack), and horizontal distance from the center-top of the head tube to that vertical line that goes through the bottom bracket (reach). The intersection point is usually an imaginary one in the air perpendicular to the top of the frame and the center of the bottom bracket This has been explained in great detail by various manufacturers and has recently gained prominence as a standard measurement included with most manufacturers' literature.
Of course, as a bicycle's stack increases, so should it's reach. Tall people are tall because they have long legs, long torsos, and long arms, which is why bicycles get proportionally longer and taller at the same time. For different kinds of bicycles ridden in different ways, one needs to know what relation the stack and reach have to one another across sizes withing a model of bikes.
In other words, this is a fraction in need of a common denominator to make sense!
I played around with calculating effective downtube lengths and making the ratio into a reach/stack percentage, but then I read this blog and found my solution. The author was comparing stack and reach among lines of road bikes as a ratio, with a ratio of 1.5 to be about neutral. anything below 1.5 is "racey" and above 1.5 seems to imply a "relaxed" geometry.
Oddly, bicycle manufacturers seem to have made no attempt to connect these things in meaningful ways for their customers. Either they know that geometry is more complex than that level of simplicity (very likely) or that the average consumer doesn't have the time, nor the mental capacity to wrap their head around that metric of comparison (equally likely).
If this theory holds any water, I can compare a few medium-sized frames that I find compelling (Kona Unit, Vassago Jabberwocky, surly Karate Monkey, etc) and find that the frame stack-and-reach ratio hover of most XC hardtail frames around the 1.4 mark. Niner's ROS 9 and SIR 9 medium frames are both 1.56, despite the fact that the former is labeled an "all mountain" bike and the latter a "XC/race" bike.
Of course, the end result of how a bike fits (pedaling) and handles (wrangling) depends on the way one sets up the saddle and handlebar position, but getting a frame that best a accommodates that position is a good start. If the frame dimensions do not yield the riding position and posture that suits your riding style, that's the wrong frame for you.
I am at this point: can I balance the fit and the handling of this current frame in a way that suits me and my riding style? If so, great! If not, I am back to shopping for a new frame. Since I am too cheap to just buy new stuff to solve my situation, this will be a long, difficult road.
