Thursday, February 3, 2011

Geek Out, Man or the Scary Truth Behind Skid Marks

All I could think about at work today was skidding on my bike. Mostly, I was thinking about it because I'm wondering how long my road tire can hold up to the abuse. I have many miles on them already and with all the extra rubble in the road (to keep most people from sliding), I think they are skidding on borrowed time. Oh. For those of you who are visual learners, check out this video:

These guys are skidding to the max. Most of them. There are a couple falls that look uncomfortable.

When I skid to check speed, my position on my bike is drastically different than what you see here. You'll notice that these folks are leaning, in some cases, over the handlebars in order to release as much weight from the rear tire as possible. This technique allows a rider to skid for just about all of eternity. Isn't that nice. Me, I have no desire to skid for that distance. I desire lots of things, but distance sliding is not one of them. When I skid, it's for one of two reasons. The first reason is to impress Kalea. The second? Because I don't want to run into the back of Dude's Subaru when I'm raging down Reed Market on my way to work. So, instead of leaning way forward like the folks on this video, I slide just to the front of my saddle and raise up 2cm, at the very moment that I slide forward and up I stop pedaling. That part is committing, especially with some speed. If you don't do this right, you'll probably hurt yourself (which I did more than I would care to admit when I first started learning). So now we are slowing down very fast and impressing Kalea and avoiding Subaru Dude. The other thing that I'm accomplishing by skidding with more weight over the rear wheel is rear tire ex-foliation. That part is not quite as amusing.

I did some research on this fixie tire ex-foliation and I learned something that I'm sure I should have learned a long time ago. Here's the part that I knew: Based on the gear ratio of my bike I have a certain number of "skid patches" on my tire. I will attempt to clarify. When I skid I always have my crank arms parallel to the ground. I can skid with either my left or right foot forward. Based on this information, it would seem natural that I would only have two spots on my tire that I skid on (the top and bottom, if you will). Fortunately, for my tires, it is not that simple. The factor that you have to look at is gear ratio. That is, the ratio of teeth on my front chain ring versus the ratio of teeth on my little cog in the back. My gear ratio happens to be 46/16. I have lots of teeth up front and less in the back. Vampire-ish if you ask me. Anyway, I have 16 skid patches on my tire. "Easy," you might say. "However many teeth your back cog has is how many skid patches you have!" Nope. Almost that simple, though: Take the lowest common denominator (in this case, it's 23/8). The denominator of that fraction is 8, so that is how many skid patches I would have if I just skidded with one foot forward. Since I can skid ambidextrously, though, AND since the numerator of the reduced ratio is ODD, I get DOUBLE THE SKID PATCHHHES!!! Geek out, man!

Folks, this is great news. This means my tire will hopefully last me a little longer and I won't have to fret about it at work. Maybe someday soon I will post a review of fixie tires that last, though. Cheers.

1 comment:

  1. I like that post....especially the part about impressing me. I am impressed with your blog as well :)