The Vital BMX Guide to Bike Parts
If you’re just getting into BMX, trying to understand all the lingo can be a bit challenging. Backsweep? Butted tubing? Freecoaster? What? To help you understand all of this, we’re going to be constantly updating this Vital BMX Dictionary so you can check it out whenever you get confused. And this is not just something for us to create. If you see a definition that could be improved or a term to add, write the definition and send it mlosey@vitalBMX.com. If it’s good, we will add it to the dictionary and give you credit.
Bar ends: Protective caps that attach to the open ends of handlebars. Some attach to the outside of the bars and others insert into the bars and use a wedge-style clamping system to hold them in place.
Backsweep: The amount of “back bend” in handlebars. The greater the angle, the more the ends of the bars angle back towards the seat.
Bottom bracket: The tube on the bottom of the frame where the cranks and bearings attach. There are multiple types of bottom brackets in BMX including American, Euro, Spanish, and Mid. A sealed bottom bracket is one in which the crank bearings are contained in a sealed case on each side of the bottom bracket. Sealed bottom brackets typically runs smoother and require less maintenance than loose-ball bearings.
Brake posts/mounts: Posts attached to the frame or forks where U-style brakes are attached. Rear brake mounts attached to the chainstays may limit how small of gearing the frame will accept; if the gear ratio is too small, the chain may hit the brake arms.
Butted tubing: A type of construction where certain areas of a tube are thicker than others. This allows manufacturers to retain strength and reduce weight.
Cable hanger: The device used on U-style brakes that connects the straddle cable to the main brake cable.
Chainstays: The tubes on a frame running from the bottom bracket to the rear dropouts. The shorter the chainstay length, the easier the front-end of the bike will pull up.
Chain tensioner: A device attached to the rear axle and frame dropouts to prevent the rear wheel from moving and the chain from coming loose.
Chromoly: A type of steel commonly used to make parts for BMX frames. “Chromoly” is short for chromium-molybdenum steel.
Crank spindle: The metal tube that runs through the bottom bracket and connects the crankarms together. Traditional spindles are made of chromoly, while titanium is a lighter-weight option
Detangler: A device attached to the rear brake cables allowing the handlebars to continually spin without tangling the rear brake cables. (Odyssey Gyro, SST Oryg, SNAFU Mobeus, etc.)
Downtube: The angled tube on a frame’s front triangle running from the headtube to the bottom bracket.
Dropouts: The slotted piece metal on a frame or fork where the wheels attach. Some dropouts have slots for 3/8” axles and some for 14mm axles. Larger axles are harder to break/bend, but they also add weight.
Drive-side: The side of the bike where the sprockets and chain are located. Many wheels and cranks are set up to work with both left- or right-side-drive.
Flip-flop hub: A rear hub with threads on both sides allowing you to easily change gearing by simply turning the wheel over and using a different-sized freewheel on the opposite side.
Freecoaster hub: A rear hub that does not “backpedal” during rollbacks like a freewheel, yet does not engage a brake like a coaster brake.
Freewheel: A sprocket mechanism that threads onto a rear hub. A freewheel allows a rider to pedal backwards to change pedal positions without engaging a brake. Freewheels also causes cranks to “back-pedal” during rollback tricks.
Front-load stem: A stem in which the handlebars attach in the front.
Front triangle: A term referring to the front-half of a typical BMX double-diamond frame (the top tube, downtube, seat tube, and head tube)
Handlebar height: The distance from the center of a handlebar’s clamping tube to the center of the grip tubes.
Handlebar width: The distance from one end of the handlebars to the other. Many riders prefer to trim bars to a custom length.
Headtube: The front tube on a frame where the forks and stem meet. The steeper the headtube angle, the more responsive the steering will be. Flatland bikes typically have the steepest headtube angles in BMX.
Hub guard: A protective guard that attaches to axles to protect the hub and spokes during grind tricks.
Intergrated headset: A frame headtube featuring built-in headset bearing cups. This allows for easier assembly and maintenance than traditional headset systems.
Rear triangle: A term referring to the rear-half of a typical BMX double-diamond frame (the chainstays, seatstays, and seat tube)
Seatstays: The angled frame tubes running from the top tube/seat tube junction to the rear dropouts.
Seat tube: The tube on a frame running from the top tube to the bottom bracket, and where the seatpost inserts into a frame.
Split-cap stem: A stem in which the outer clamp is two separate pieces with a gap in the center to reduce weight.
Straddle cable: The cable used on U-style brakes that runs between each brake arm.
Titanium: A lighter weight material used to make parts, from frames to bottom bracket spindles, to pegs. While titanium weighs less than chromoly, it is considerably more expensive.
Top-load stem: A stem in which the handlebars rest on top of the stem.
Top Tube: The tube on the frame running from the headtube to the seat tube. The length of the top tube determines how “roomy” the front-end of the bike feels, and it contributes to how easily the front-end of the bike lifts off the ground. Generally the taller the rider, the longer the top tube. Flatlanders typically use frames with shorter top tubes so the frame comes around quicker on tailwhip-style tricks, and making the bike easier to straddle during certain tricks.
Upsweep: The angle of “up bend” in handlebars. The greater the angle, the more the ends of the bars angle up.
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