Sprockets

BMX sprockets: the front teeth in a single piece

At the front of a BMX race bike, two schools of thought sit side by side. A chainring bolts onto a spider, which is itself part of the crank. A one-piece sprocket brings the teeth and their support together in a single machined part that fixes straight onto the spindle or the crank arm. Fewer parts, less hardware, a stiffer assembly — but a tooth count locked in at the moment you buy.

Sprocket or chainring: what separates them

A chainring is replaced on its own, without touching the spider: changing gear means undoing four or five bolts. A one-piece sprocket is changed complete, but it removes the spider-to-ring interface, a long-term source of play and noise. On a training drivetrain that gets stripped down often, the chainring stays the more flexible option; for racing, the sprocket wins on stiffness and on a cleaner build.

The mounting types

• Spline drive: the sprocket slides onto the splines of the crank spindle, in 19, 22 or 24 mm, and is locked by the spindle bolt or a clamping collar. This is the most direct and the stiffest fitting.
• Bolt drive: the sprocket bolts onto inserts built into the crank arm. The fitting is specific to the crank brand, so check it before ordering.
• Integrated spider: some sprockets follow the outline of a chainring but with arms machined from the billet, mounted on a proprietary spider.

Tooth counts and gearing

In BMX race, sprockets usually sit between 39 and 45 teeth. Paired with a 15 to 18 tooth cog, they cover most of the gearing used in competition: 44x16 gives 2.75, 41x15 gives 2.73, 43x15 climbs to 2.87. Two very different tooth pairings can therefore produce an almost identical ratio — the difference then comes down to weight, chain length and wear, since a small rear cog wears faster than a large one.

Materials and machining

7075-T6 aluminium dominates the category: CNC machined from billet, cut away to save weight, anodised to resist chain abrasion. Some sprockets get profiled or chamfered teeth to improve chain engagement, others a harder surface treatment on the contact zone. Training versions in 6061 aluminium are heavier but noticeably cheaper.

Chain compatibility and alignment

As with any front tooth profile, thickness has to match your chain: 1/8" or 3/32", with no mixing. Then check that the plane of the sprocket lines up with the rear cog; that alignment is corrected with bottom bracket spacers, never by forcing the chain. Finally, check clearance between the sprocket and the chainstay, particularly on the larger tooth counts.

The brands available

Tangent offers one-piece sprockets widely used in race, in several finishes. Box Components covers spline drive fittings in 19, 22 and 24 mm. Insight equips the younger categories on a contained budget. Elevn and Stay Strong play the cut-away design card, with colours to match the rest of the build.

The BMX RACING advice

Before changing tooth count, measure your current gearing and note how the bike feels out of the gate: that usually tells you more than a table. Send us your crank spindle diameter, the tooth count you have in mind and your chain format, and we confirm compatibility before dispatched within 24 to 72 hours. Payment in 2 or 3 instalments.

A tooth at the front is not a tooth at the rear: our article on BMX race gearing puts numbers on the gap.