Off-Road Fixed Gear Setup, Revisited -- Part I by Matt Chester Well, Here
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Off-Road Fixed Gear Setup, Revisited -- Part I by Matt Chester Well, here we go again. I'm here to revisit my thoughts on setting up a fixed gear bicycle for off-road usage. It's been a while since I last wrote on this topic, and now I have a few more years of experience (and hopefully of wisdom as well). This is a two-parter: this first part will cover some basics regarding your frame, fit issues, gearing choices, and crank length. The second part, appearing in the next issue of 63xc.com, will concentrate on the more empirical, nuts-and-bolts territory of component selection. Fixed gear off-road is gaining converts, mostly from the singlespeed MTB world. Its growing popularity shows, albeit in a small way, how everything is cyclic (no pun intended). You see the same cycles in politics, music, design, and other areas. Everything is impermanent. As cyclists, we are just following trails that were opened up long ago by other riders, riders who didn't have access to the myriad of component choices that we do now. Before getting started, I thought I might say a few words about the fixed gear 'attitude'. While exploring earlier, simpler forms of cycling, you should always remember the Fixer's Mantra: 'Calm down.' Really. Riding a fixie off-road is pretty daunting at first, and you'll need a new set of skills to ride successfully. (By 'successfully' I mean: 'without hurting yourself'.) Stripping things to the bare essentials certainly makes them 'simpler'. It doesn't necessarily make them 'easier' or even 'better'. It takes patience and repetitive practice to bring an ethos of 'doing more with less' to fruition. So why bother to acquire those new skills? Fixers will tell you that a fix is more efficient than a geared bike. Well, that's true--up to a point. The fix certainly scores high in foul weather or icy conditions. As an everyday offroad machine, however, its simple setup often works out less than ideal from a performance perspective. So what? I'm not worried about performance. My own love of fixing comes from the fact that I like to cycle, and a quiet, basic machine appeals to me. My good memories of cycling have little to do with equipment and everything to do with experience. Ride your bike to ride your bike. Do it because you want to. If you approach riding with a relaxed, light disposition rather than with an aggressive mindset, you'll really enjoy yourself. If you enjoy yourself, you'll stick with it. Sticking with it is good. Simple enough? Frame notes I assume that readers of this site are already familiar with the basic points of singlespeed and fixed gear setup, in particular the ways that the need to tension the chain impacts on frame choice. (If not, you can find a nice primer in the sidebar.) I'll take the opportunity to repeat, however, that no fixer can use chain tensioners like the Surly Singleator, Soulcraft Convert, Paul Melvin, or dummy derailleurs which are common in the singlespeed world. If you set up an external tensioner on your fix and try to apply backpressure to the pedals, tension in the bottom run of chain will force the thing out of the chainline. The result will be a broken tensioner and often a bent derailleur hanger... or worse. So, no tensioners! OK? You can still use track ends/horizontal dropouts, eccentric bottom brackets (EBBs), or eccentric hubs. Now, let's discuss fixed-gear specific aspects of frame design. 1. Seat tube angle and saddle position I built my freewheeled singlespeed 'cross bike with a steep seat tube--75 degrees, believe it or not. I really enjoyed riding it. I loved the quick transition between seated and standing climbing and, once my hamstrings were used to the position, I thought I'd never ride a slacker seat tube angle. But when I made the full-time change to fixed off-road, I found that my 'cross bike made descending hard. Since there was no way to get behind the saddle, I had to stay seated, putting my weight as far back as possible and pedalling all the way. Descents on gnarly terrain made me feel like a ski jumper, making panicky stabs at my front brake as I hung over the front wheel and tried to keep the whole flailing mess together. High speed fireroad descents, where clipping out and 'coasting' were impossible, would find me bunched forward on the bike, weighting my hands excessively while trying to maintain a non-freakish-looking level of blurry high-RPM spinning. When I built myself a new frame, I utilized a more traditional 73 degree seat angle. The difference was marked. I'm no star on a bike, but I was much more comfortable with more weight on my rear end and a lower center of gravity. Nor did I notice any ill effects on climbing, leg speed, or whatever. The new position was different, but suited to a broader range of situations. Now, seat tube angle is one of the grayer aspects of frame dimensioning, as many external variables can affect the relationship between your saddle and your pedals-- seatpost layback, saddle position, position of foot on pedal... My advice is to err on the side of slack. Keep your seat back and set the bars a bit higher than on your coasting bike. I'll return to this point when I talk about fit later on. 2. Bottom bracket height Bottom bracket height is more of an issue for fixers than coasties. This has less to do with handling characteristics than with pedal clearance, a quality which is also affected by crank length, pedal choice, and tire choice. However, while these last three are easily changeable according to the rider's preference, BB height relates to the frame design and can't easily be changed. In practice, it's hard to reach a fair measure of BB height, because it can be affected by tire choice. Most framebuilders prefer to talk about 'drop'. This term denotes the vertical distance between the bottom bracket center and a line passing between the hub centers. A traditional real world 700c road bike (a Rivendell, say, or a classic British tourer) would have a drop of around 80mm. A real roughstuff 700c cyclocross bike would have much less drop, say 60-65mm. Since the 'cross bike will likely be set up with larger, taller, knobblier tires, the bottom bracket will gain even more height. A higher BB gives more pedaling clearance, which is advantageous in a cyclocross race where aggressive cornering and rough terrain are all part of the hour's worth of extreme effort. Fixers ride off-road without being able to 'ratchet' the cranks or to hold our feet in the '3 and 9' position when coasting through rough bits, so lots of pedal clearance seems like a good idea. But, guess what? Even on a frame with an insanely small drop--perhaps even a negative one, like on a 26" wheeler with a BB above the hub center--you'll still strike a pedal sometimes. That's just reality. The point is: don't give in to fear. Just get out and ride a lot! The real trick to getting through obstacles on a fixie is your own ability. Practice. That's it. The standard ranges of drop on existing off-road bikes are more than adequate. I myself ride a bike with 70mm of drop and a 700 x 35c tire. (70mm is pretty normal--for a road-specific machine.) Of course, I use 165mm cranks despite my 6'2 height. But we'll talk more about cranks later. 3. Chainstay length Chainstay length is subjected to incessant analysis. 'Shorter chainstays are better for climbing!' crows the internet discussion forum sage. Utter nonsense! No single aspect of frame design will enable you to predict a bike's handling characteristics. (If that were really the case, my job would be much easier.) In the real world, all aspects of frame design work in concert with one another. Adjust one, and the others are affected. Why am I wailing on the oft-repeated myth of the 'short chainstay?' Because there's more to building a good off-road fix than lopping the chainstays wicked short. Here are the things that I've learned from experience. The first is that you are seated on a fixed gear. A lot. On rough terrain. Any frame design which tucks the rear wheel underneath you is likely to produce an uncomfortable ride. The second is even more important--to me, at least. You will find that the shorter the chainstay, more difficult it is to keep the rear of the bike tracking straight while pedaling at some ungodly RPM down a mountain pass. It is possible to combine a longish rear end with good climbing. The old guys knew this already. I have learned, too. 4. Frame overview So, let's review. Based on points 1-3, it seems that a stable, conservative, somewhat traditional, commonsense frame design is best. It's no longer the 1980s! There's no reason to take things to the extreme and then declare 'it's better because--' Nope. If you look back to the days when almost everyone rode the dirt on a fixed gear, or even just back to the early days of mountain biking when adventure, self-sufficiency, and fun were the order of the day--well, that's the way it was.