CILOYU 35-Series Mini Bike Rear Sprocket 40T 37mm Bore — 6-Hole Alloy Replacement for CT100U/DB30/MBX10

CILOYU's 40-tooth rear sprocket for 35 roller chain is a precision machined replacement designed to improve power delivery and durability on small-displacement mini bikes and go-karts.

This replacement rear sprocket is built for riders who need a reliable, compact 40-tooth gear with a 37 mm center bore and a 49 mm (1.92") bolt circle to match many popular mini bike frames. Machined from a stout metal alloy, the design includes six evenly spaced mounting holes for easier alignment and compatibility with a wide range of Coleman, Baja, Motovox, Monster Moto and other mini bike models. Because this sprocket uses 35-series roller chain, it can be trimmed to fit shorter drives, and its smaller tooth count compared with larger factory gears will change final drive characteristics.

How will swapping to a 40T sprocket affect my mini bike's ride?

Changing to a 40-tooth rear sprocket alters gearing so the engine runs at lower RPM at a given road speed, which can reduce engine strain and improve straight-road speed potential. Expect a quicker engine response at lower speeds and a different top-speed/acceleration balance than a larger sprocket.

• Lower engine RPM at cruising speeds for potentially better efficiency.
• Faster top-speed potential on flat stretches compared with much larger sprockets.
• Acceleration feel may become slightly sharper off the line depending on front sprocket size.
• Chain length may need trimming to match the new sprocket's smaller diameter.

Will this sprocket fit my model CT100U, DB30, or MBX10?

The sprocket is made to cover many popular mini bike and go-kart models, including Coleman Powersports CT100U, CC100X, RB100, DB30 family machines, Motovox MBX10/MBX11, and several Monster Moto/ Mega Moto models. Compatibility depends on matching the 37 mm center bore and the 49 mm bolt-circle mounting pattern; measure your hub before ordering.

• Center bore: 37 mm (1.45")—matches corresponding hubs or can be adapted with sleeves.
• Mounting holes: 6 holes with 49 mm bolt-circle spacing.
• Chain size: compatible with 35-series roller chain; chain shortening may be necessary.
• Common fit for Coleman, Baja, Motovox, Monster Moto, and similar mini bikes.

What are the construction and design highlights that make this sprocket durable?

The sprocket is crafted from a heavy-duty metal alloy and precision-machined for consistent tooth profile and mounting alignment. The thicker material and 6-hole mounting pattern lower flex under load, improving longevity compared with thinner aftermarket pieces.

• Thick, alloy construction resists deformation under torque.
• Precision-machined teeth for smoother chain engagement and less wear.
• Six-hole mounting distributes load evenly across the hub flange.
• Improved hole spacing designed for straightforward installation.

How should I install and size the chain when switching to this sprocket?

Installation is straightforward if your hub matches the 37 mm bore and 49 mm bolt circle; align the six mounting holes, secure with appropriate fasteners, and trim the 35-series chain to the correct length. Check chain tension and alignment after a short test ride and re-torque hardware to factory specs.

• Confirm hub bore and bolt-circle measurements before mounting.
• Shorten the 35 chain as needed; ensure proper rivet or master link installation.
• Set correct chain slack per manufacturer recommendations after fitting.
• Re-check mounting bolts and torque after initial run-in ride.

Who is this for: This CILOYU 40T 35-chain rear sprocket is aimed at mini bike owners, small go-kart riders, mechanics, and DIY enthusiasts who need a compact, sturdy replacement sprocket for Coleman CT100U/DB30 series machines, Motovox MBX models, and comparable small-displacement bikes. Choose this part if you require a shorter, durable rear gear with a 37 mm bore and improved six-hole mounting for easier fitment and a different gearing profile than larger factory sprockets.