By: Tools of the Trade Feb 1, 06:13 AM |

Jared Porter has spent most of his life in and around the bicycle industry. A graduate of the Massachusetts College of Art and Design, Jared has worked in all arenas of bicycle fabrication with such companies as Merlin Metalworks, Vicious Cycles, Willits Brand Bicycles, and his current position as the Production Manager at Serotta Bicycles in Saratoga Springs, NY. Below is the first in a series of Tech articles Jared is writing that focus on his own bicycle building project.

I have been thinking about building a new frame for myself. I build frames for my customers everyday, with painstaking care to be sure they are getting their dream bike. So it’s a little strange for me because I am trying to figure out what I want to make when I am so used to figuring out what others want. A logical place to start is by asking myself why I’m building a new bike in the first place. This time, I want a cross bike, though racing will only be a small part of what it is used for. I need to consider what I want this frame’s primary function will be and the secondary things it needs to be good at as well.

I’m starting with a cross bike platform and narrowing my focus as I go along. The idea of racing cross next season is appealing. Though I have never participated in a cross race, I feel a slight twinge of guilt as I stand on the sidelines egging my suffering friends on as I drink beer. It seems only fair to reciprocate. So racing is a nice thought, especially when cross season is a long way off, but I need a fall back plan for this bike. I will also use this bike for exploration of the many dirt roads that lace through the foothills of the Adirondacks where I live. The other use will be commuting in the winter when my fixie is outmoded by slush and snow.

As a frame designer and builder I always get nervous about a customer who wants a bike to be too many things. Frames designed to excel in certain circumstances have degraded performance in other disciplines. I’m getting into the realm of the Swiss Army knife if I go much further down this multi use road. As an example, it’s very tempting to try and fit a little touring geometry into the mix. The problem is that touring geometry is at odds with the sporty handling I’m looking for. Additionally, my enthusiasm for cross racing may evaporate after I puke a lung on the first lap race number one. So the question is: what will I be doing with this bike ninety percent of the time? My honest answer is riding on dirt roads. So, that’s what the frame needs to be good at. This is an important exercise for anybody in the market for a new bike. Visualize what you will really do with a new bike and buy one accordingly.

Materials are the next consideration. I have decided to build this frame out of steel. The Columbus Niobium tubing we use at Serotta is great to build with because it is light, strong, and easy to fabricate with. I also want to try using some tapered S-bend chain stays on this frame rather than the straight, ovalized stay we normally use on cross bikes. I have the S-bend chain stays on my fixed gear and really like the comfort they provide. The challenge will be squeezing as much tire clearance as possible out of the stays. I will use 16mm single tapered seat stays to give the brakes responsiveness while keeping the rear of the bike compliant. Up front I will use a tapered, triple butted seat tube that is 35mm at the bottom bracket and 32mm at the seat top. This will keep the bottom bracket from wagging to and fro, while using a 27.2mm seat post, which is flexible, and should enhance the shock absorbing qualities of the rear triangle. The down tube is where things get burly. A 38mm double butted down tube will be employed to keep the front end nice and stiff. The top tube is triple butted and is oval in the horizontal plain at the head tube. So what does all this mean? Essentially the frame will be built with comfort in the rear triangle while the front triangle will we stiff to control rider input from the pedals and the handlebars.

The next aspect to consider is geometry. I want this bike to feel light at the bar, so minor changes in direction can be achieved with minimal input. I will use a relatively steep head angle of 72.5 degrees combined with my 47mm rake cross fork. This will allow the bike to turn without having to lean it excessively to initiate turns. The down side is that these handling traits require more attentiveness by the pilot. The bottom bracket drop is another element that affects the performance of the bike radically. Drop is the distance the BB sits below the horizontal line made between the front and rear axle. Many cross bikes have smaller amounts of drop, which equals a higher BB. This helps avoid pedal strikes to the ground and also helps the bike have better slow speed agility. For my bike I am going to drop the bottom bracket. This is in an effort to gain back a degree of high-speed stability as a lower bottom bracket lowers the center of gravity. I also think a lower BB will help me on mounts and dismounts when I am racing. I will be using a slightly slack seat tube angle in order to bias my weight over the rear wheel slightly. This will keep the weight off my hands on long rides and keep the front wheel from knifing into the soft ground on wet muddy courses. A rear weight bias will also keep the front wheel tracking straighter with less attention on gravel roads. The chain stays will be short to cut down the wheelbase and keep acceleration snappy. Doing this will make the bike more twitchy at speed but increase traction at the rear tire and make it easier to bunny hop those barriers (yeah right).

The last thing I have to mull over before drafting my new frame is the cable routing. Generally I like down tube routing for the shifter cables, but I’m going with top tube routing for this bike. There are a couple of reasons for this. First of all, top tube routing interferes with the front brake wire less while the bars are turned. A triple stop can also be used on both ends of the top tube, cutting down on the number of cable stops on the bike. The rear derailleur cable will then split off down the drive seat stay out of the muck that will cake on the frame during muddy races. The front derailleur routing will come around the back of the seat tube and terminate on a down tube shifter boss allowing me to bolt a cable stop with barrel adjuster for fine tuning. Down below the front derailleur band clamp on the back of the seat tube will be a pulley will convert the cable back to a bottom pull for a standard road derailleur. The brake will then be routed in standard fashion on outside slot of the triple stop on the non-drive side of the top tube.

Now that I have decided what I want and how I want to make the frame I am really excited to start building. The process of narrowing focus to what is really important is essential and was a fun exercise for me. The things that were covered are valuable for anybody approaching the purchase of a new bike whether it is custom or stock, complete bike or frame only. If you do this before spending any money on a new bike you can be confident that the end result will be better.