Adaptors

BMX race adaptors: fitting parts that were never meant to meet

BMX race runs several standards in parallel: three axle diameters, four bottom bracket types, two disc mounts. Changing a wheel, a fork or a frame is enough to create a mismatch. Adaptors and reducer bushes close those gaps cleanly, without forcing parts that were not drawn to work together.

Wheel axles: 10, 15 and 20 mm

At the rear, the 10 mm axle is still the BMX race norm. At the front, modern forks often take a 15 or 20 mm through axle, while entry-level hubs and training wheels stay on 10 mm. Reducer bushes step you from one standard down to another:

• 20 mm to 15 mm reducers for a through-axle fork
• 20 or 15 mm to 10 mm reducers for a conventional hub
• Width spacers to take up play between the fork dropouts
• Replacement axles and end caps for 28 and 36 hole hubs

Bottom brackets: moving between standards

Four bottom bracket standards coexist: threaded Euro BB, Mid BB, Spanish BB and American BB. Add to that the crank spindle diameters, 19, 22 or 24 mm depending on the brand. Bottom bracket adaptors and spacer kits let you install a recent crankset in an older frame, provided you check the shell width and the chainline first. A badly spaced crankset wears the sprocket and chain long before their time, while a few euros of spacers solve the problem outright.

Braking: disc, V-brake and mounts

Two disc fittings coexist: ISO 6-bolt and Centerlock. A Centerlock to 6-bolt adaptor lets you run a standard rotor on a Centerlock hub. At the caliper, mount adaptors handle the move from an IS to a post mount fitting and any change of rotor diameter. On V-brake builds, bushes and boss spacers take up pad alignment on 406 or 451 rims.

Steerer, seat post and valve

The other common adaptors cover the rest of the bike: steerer reducer bushes to fit a 1"1/8 fork into a wider head tube, headset spacers, seat post shims to drop a 25.4 mm post into a 27.2 mm seat tube — to be matched with the right BMX seat clamp — and Presta to Schrader inflation adaptors so you can use a workshop pump or a garage compressor. Those last ones naturally live next to your BMX valve caps.

Choosing without getting it wrong

The rule is to measure before ordering, never the other way round. A vernier caliper gives you the true diameter of a steerer, a post or an axle; a shell width is taken with the cups removed. Then note the make and model of the frame, fork and hub: those details decide which bush you need. An adaptor compensates for a difference in standard, not for a bent or misaligned part.

Brands available

• Box Components: well documented axle bushes and brake adaptors
• Promax: caliper mounting solutions and brake hardware
• Tangent: spacers, bushes and workshop small parts
• Position One: axle adaptors for its own hubs and forks
• Onyx: end caps and axle kits for its hub range

The BMX RACING advice

Send us the reference of your frame, fork or hub along with the part you want to fit: we check compatibility before you order, and we tell you when an adaptor is not the right answer. Being multi-brand, we know the quirks of each range. Dispatched within 24 to 72 hours, you can spread the cost over 2 or 3 payments available; the tools themselves are in our BMX tools section.