HOW TO SKID

What is actually happening

On a fixed gear the rear cog is locked to the hub, so the cranks and the rear wheel are the same rotating object. Resist the pedals hard enough to overcome the tyre’s grip and the wheel stops turning while the bike keeps moving. That is a skid: the same patch of rubber dragging along the road.

Which is why the interesting question is not “how” but “how many patches” — because it decides how quickly you destroy a tyre.

Your gear ratio decides how many contact patches you get

Put the chainring and cog into a fraction and reduce it. The denominator that survives is the number of skid patches. That is the number of distinct places on the tyre that ever touch the road while the wheel is locked.

• 48 × 16 reduces to 3/1 → 1 patch. One spot on the tyre takes everything.
• 48 × 17 does not reduce → 17 patches, spread around the tyre.

Two teeth of difference, and the tyre lasts an order of magnitude longer. Work out your own with the skid patch calculator, and read the longer explanation for why ambidextrous skidding only doubles the count when that denominator is odd.

The parts that have to be right first

Skidding loads the drivetrain in the direction it is least used to. Three things carry that load:

A lockring, correctly fitted. The cog threads on clockwise and tightens as you pedal; the moment you resist, the force reverses and tries to unthread it. The lockring is reverse-threaded so it takes that load instead. Why it is reverse-threaded is worth reading before you put weight on it. A cog without a lockring will come off.

A chainline that is actually straight. Sideways load goes up during a skid, and a chain running at an angle is the one that jumps off. Chainline calculator — measured values only, no estimates from spindle length.

Matched chain and sprocket width. 1/8″ throughout is the usual track answer. A 3/32″ chain on 1/8″ teeth has play, and play is where a chain comes off. See 1/8 vs 3/32.

The technique, briefly

Weight forward and up out of the saddle so the rear unloads, cranks near horizontal, then resist the forward pedal. Unloading the rear is the part people skip — with your weight over the back wheel it simply grips, and you are just pushing against your own drivetrain.

Start from a slow roll on a surface you have already checked. It takes far more force than people expect the first time, and rather less than they expect the second.

What it costs

Rubber, mostly, and unevenly. A one-patch ratio can square off a tyre in a single session. Riders who skid regularly tend to pick a ratio with a large odd denominator for exactly this reason, and rotate the tyre before it goes through.

Gear ratios, tooth counts and the parts behind them are at the index; to check whether a specific cog, lockring and chain go together, use the fit check.