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  • Notes On Bike Deraileurs

    August 21, 2023

    Exactly three months ago, I had a rather major bike accident that landed me in the ER with an orbital fracture, a substantial temporal laceration that required 5 stitches, an absolutely shredded forearm, and a somewhat torn up back. I also suffered damage to my knee and elbow. Since then, I've been focusing on healing and scheduling appointments with specialists. Thankfully, I suffered no permanent damage that I am aware of, and remarkably, I had no brain injury. I count myself incredibly blessed that, with the exception of the slight tenderness of my temple, and the occasional acting up of my knee, I am no longer in pain and have healed up properly. I have scars on my forehead, forearm, shoulder, and probably my back, but other than that, there are no visible symptoms of my injuries.

    Today, I finally pulled my mountain bike out of the garage to inspect the damage after letting it sit for a few months while I dealt with my physical health. Unfortunately, my bike suffered about as many and about as severe injuries as I did. It slid a number of feet with me after I went down, and as such it has many scratches on the handlebars. The handle grips are torn up and twisted, the plastic shifter levers are dented and peeling, and the right brake handle is bent. The seat has two major rips in it, and the chain was dangling on the back gears.

    I am not a mechanic, and I have never done any bike maintenance before, but I didn't want to just roll my bike into a shop and let a technician take care of it; I personally wanted to be the one to repair the damage because I firmly believe that everyone should know how the machines that they depend on actually operate. I hold this view not only with computers, which is certainly my main specialty, but also with other technology such as cars, and, well, bikes. I like to know how things work, and I don't like blindly trusting my machines without knowing as much as I can about them. This makes it much easier to troubleshoot when things go wrong.

    I put the chain back on my bike first. This was actually extremely easy because the rear derailleur is spring loaded such that the bottom pulley can be rotated about the axel enough to give the chain enough room to be put back on the front sprocket without being tight. With the chain in place and on the proper sprockets, I proceeded to go for a quick test ride around our cul-de-sac. I suspected that the rear derailleur was probably out of alignment, and my test confirmed this: shifting was rough and sometimes didn't even work at all. The chain slipped onto the higher sprockets sloppily, and it rubbed against the derailleur on the lower sprockets.

    Nothing looked obviously bent, so some tweaking and tuning was all that was necessary. Of course, I have no idea how to tune a bike, so I spent most of my time in the garage doing research about the bike's anatomy. Instead of looking up the problems and asking my search engine for solutions, I simply tried to learn as much as I could about the drivetrain so that I could diagnose it myself. In this blog post, I want to jot down some of the terminology I learned for future reference. I was specifically doing research on mountain bikes, so some of this terminology may be specific to them.

    When I propped my bike upside down on its saddle and handlebars and watched the rear derailleur up close as I spun the gears, I could see that it appeared out of alignment with the sprockets, leaving the chain off to one side on the sprockets and not very well centered. This is what was causing my shifting troubles, and would explain why sometimes the chain would skip a gear and go up to the adjacent one.

    I spent a few minutes adjusting the indexing knob, and after a few test runs, my shifting began working properly. In fact, after tuning and playing with the various screws and knobs on the rear derailleur, I can confidently say that my bike now runs smoother than it has in a long time. Of course, the chain is rusty and the gears are significantly worn, so I don't expect it to work perfectly. I have had this bike for many years, and I have no doubt that some new components would be good for it. But I do believe it has a at least a few more years of life in it.

    When I finished tuning the rear derailleur so that it runs smoothly, I repaired the rips on the seat by carefully covering them with duct tape. I also trimmed the peeling plastic off of the shifter levers and picked rocks out of the handle grips.

    I was quite surprised at both the simplicity and the complexity of my bike. At its core, it is an extremely simple design, and the derailleurs strike me as somewhat crude because at first glance they appear to just push the chain across the sprockets, but upon closer inspection, I found a sophisticated drivetrain that needs careful tuning to run smoothly, and the mechanics of the shifters are surprisingly elegant. The bike is no longer a black box machine to me, and that I am glad about.

    Tomorrow I will be taking my first serious bike ride since my accident. This time, I will be wearing a helmet. Both my bike and I have scars, but we survived and are getting back up again. There is severe cosmetic damage to my bike, but I have no intention of replacing it or repairing that damage, because it does not impair the functionality in any way, and it serves as a good reminder to be careful. Life is precious, and it can so quickly change or even end. When I recount the events of the evening of May 21, 2023, I am often reminded that I should have died. A blunt collision of skull and cement at high speeds is not something most people are expected to get up and walk away from, but by the grace of God, I did.

    In the future, as I continue to ride, proper bike care and maintenance will be important. This post is simply meant to serve as a quick reference to me, and if I may offer to my future self the most important takeaway from my repairs, it is this: when shifting issues arise, first try rotating the indexing adjuster—the knob at the base of the derailleur where the cable goes into it—by about half a rotation in either direction and going on a test run. Repeat this until satisfactory shifting performance is obtained. This should solve a majority of any alignment issues in the event of another accident, although I hope there is no such accident.

    © 2019-2024 Jordan Bancino.