The Physics of Skidding

After learning to skid for myself, I feel the knowledge that I've obtained on forums and fixed gear websites did not do a sufficient job in covering all necessary information of the skidding process, or the pre-skidding process. And so, I've set it out for myself to create a little something detailing the basic 'physics' of skid stopping. Fragments of information from different places and ideas formed by my own experience.

Basic
If you're just starting out at learning to skid, or have been practicing with failure, there are things you must look into. Firstly, your gear ratio and skid patches. Gear ratio is the relationship between the number of teeth of two gears, in this case, your chainring and your cog. In a higher gear ratio, the number of teeth will be more significantly different, thus making it harder to pedal your bike (i.e. a 56 teeth chainring and 14 teeth cog). In order to skid, you must have a gear ratio that your leg strength can overcome, and even though you may be able to skid at a high gear, there will be greater stress on your leg muscles and cartilage and you will be tired and sore in the long run. You should find a good ratio that enables you to go at a moderately good speed, but also allows you to skid with some ease. Everything revolves around the strength of your legs and the gears needed to accomodate it.

Skid patches refers to sections on the wheel that allows you to skid. Depending on your chainring and cog combination, you will have more or less skid patches. For those who have only 1 skid patch, they can only skid on one section of the wheel, so their tires will wear in the same spot. Here is a very helpful skid patch graph to determine what gears you need for more skid patches. More skid patches mean you can skid in more places, and distribute the stress of skidding throughout different places of your tires.

Skidding is easier if you have clips. If you don't already have clips installed on your pedals, do so. You will be surprised at how much power and control they give you. Most fixed gear riders prefer clips to clipless pedals. It will take a little time to get used to clipping in and out of your clips. Remember not to over tighten your clip strap as you will need room to clip in and out.

I've also come to find that the type of tires you have play some role in skidding, or at least, learning to skid. Some tires have more pavement resistance than others. I had really cheap high-resistant tires while learning to skid, even though I managed to learn on them, after switching to some better tires, I'm skidding with much better ease, I have Gran Compe tires on right now. Many long time riders uses Gatorskin and Victoria Rubino for regular fixed gear skidding because of their wear resistance.

It is recommended to have crankarms in 165mm for fixed gear riding. Because fixed gear cranks don't stop rotating, this will prevent them from striking the ground when turning. I've done some pretty aggressive turns with 165mm. You can probably get away with 167.5mm. However, if your bottom bracket is lower because you have 650c or smaller wheels, a shorter crankarm is recommended. Typically track bikes will have higher bottom brackets because they are specially made with extra clearance to handle hard turns, allowing possible use of longer crankarms.

Skidding
Skidding is done easiest on wet grass or wet pavement, if none are accessible, you can do it on regular grass or really smooth pavement... or hose down your driveway! Grass is hard to pedal in, so when practicing skidding in grass, bike down regular pavement and into the grass then proceed to lock in your pedals and practice skidding.
Skidding isn't just displacing your weight onto the front wheel, but pressing against it and pushing your legs against your pedals, all at once. You should get used to the rotation of your cranks, wait until it reaches close to horizontal position then place your lower abdomen onto the stem and push into it, at the same time lock in your pedals and push hard against it with your strong leg in the back. Keep practicing doing all these motion to get used to the flow and the process. Each time slightly changing the movement, i.e. pushing harder, locking in your pedals at a slightly different position.