BMX Fork: Everything to Know

What are the types of fork material?

  • 4130 chromoly is widely used in both freestyle and racing. This material is strong, durable, and affordable. It allows a bit of flex to absorb hard impacts while remaining very durable.

  • High-tensile steel is commonly found on entry to mid-level BMX bikes. This is durable enough for an entry level rider but not made for large impacts. This is a bit heavier than 4130 chromoly as well.

  • Carbon fiber forks are commonplace in  higher-end BMX race bikes. They are very light and rigid, which helps the power transfer to the wheels. Carbon fiber forks are a bit more expensive than chromoly and not as durable.

  • Aluminum forks are found in the racing world as a chromoly alternative but they do not have the strength/weight ratio as the carbon. They are a bit more affordable than carbon, a bit lighter than chromoly, but typically not as strong as either.

Fork Geometry

Fork height essentially refers to the length of the fork leg. This is measured from the top of the crown race to the center of the drop out. This determines the front end ride height and affects the steering. A taller fork height reduces the headtube angle, therefore creating a more relaxed steering feel.

Steerer Tube Length is exactly that; the length of the steerer tube. A longer steerer tube allows for more room for adjustment. This can be useful for those running a gyro, if a headtube is taller than normal, or those simply wanting to run a higher cockpit. A steerer tube can be cut down if needed or simply add more headset spacers as needed.

Bearing Race can be either integrated in to the fork or not. If a fork does have an integrated bearing race, it is to only be used with an integrated headset. If your frame has a standard headtube, you must use a fork without an integrated race. These forks require a press-on race, which is included with all headsets (integrated or standard).

Fork Offset is the distance between the front axle and the center of the fork leg. This affects the wheelbase of the bike as well as the "responsiveness" of front-wheel maneuvers. A shorter offset is generally preferred for riders doing a lot of tricks on the front wheel as it's more manipulative, while a longer offset provides a more stable feel, generally preferred by riders at higher speeds.

Dropout Size is either 3/8" (10mm), 14mm, or 20mm. 14mm is rare these days as 3/8" is the most common in both freestyle and racing. 20mm, however, is growing in popularity in the racing world with the idea being that it makes for a stiffer front end, again, increasing the power output to forward movement connection.

How tight should my compression bolt be?

The compression bolts are used to take the extra play out of the headset before tightening down the stem. Over tightening the compression bolt can damage it and/or the headset. It should be snug enough to get rid of any play in your headset, but not so tight that the cockpit can't spin freely.

The video below goes in full depth on everything you need to know about forks, including fork height, offset, steer tube length, bearing race and more.