Filing Pedals For Greater Performance

Written by Boston Biker on Jun 13

Tommymoose over at Bostonfixed has come up with some fun information about pedal strike (anyone who has ridden fixed knows that when you make sharp turns this is a danger). His solution, file some metal off the pedals! Not only that but he went through the trouble of calculating EXACTLY how much you need to take off to get the performance angle you need. His handy work is reposted below by permission. Way to go tommy!

I’ve got 170mm cranks (nothing out of the ordinary) and my pedals have made contact with the pavement a few times when pedaling hard and turning (I know this happens to almost everyone at some point). They only grazed the ground enough to shoot sparks, not enough to buck me or anything, so I got an idea. I took a file and just shaved down the edge that makes contact to allow a little more clearance when turning. I’m new to road bikes, so this might be common, but I felt like nerding out wanted to know exactly how much “harder” this lets me pitch my bike while turning.

I took some measurements, did some trig, and came to the conclusion that with the crank in the fully verticle position, my un-modified pedal makes contact when the bike is at a 65.5 degree angle to the ground. I took off about 4mm from each edge at an angle and found that the bike now 63.8 degrees before there is contact… a gain of 1.7 degrees. Its not much, but this is a ~2.5% increase in bike pitch angle. This doesn’t really matter at all for the type of riding I do, but maybe, just maybe it’ll prevent me from slapping the road a few times(I guess I won’t know!)

To get a baseline for what angle your bike needs to make contact with the ground, stand your bike up straight with your cranks vertical and take your X and Y measurements, then the equation is –

angle = 90 – tan^-1(Y/X)

tan^-1 is inverse tan… 2nd Tan button for anybody that still has their TI-83’s haha
Y = vertical distance from ground to bottom corner of pedal.
X = horizontal distance from center of bike to bottom corner of of pedal

Then to get your new angle, ADD the distance of how much material you took off vertically to Y and SUBTRACT what you took off horizontally from X. The result should be a smaller angle than last time, which is good. If you want to know how much tilt that represents from vertical, just subtract it from 90.

He even went so far as to send me this awesome table of data that shows various angles of strike for various pedal lengths. (download the Excel file here)

Tags: filing, math, pedal strike
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