Quick answer: do not identify a rental-kart sprocket from tooth count alone. Before ordering, confirm the chain size, number of teeth, centre bore or axle fitment, mounting pattern and any offset. Two sprockets can have the same number of teeth and still be completely different parts.
If you are replacing a worn sprocket, take the measurements before the old one disappears into the scrap bin. It is considerably more useful while it is still sitting on the bench.
Isolate the kart first
Switch the engine off, isolate the kart and prevent the rear axle from turning before working around the chain and sprockets. Never inspect or measure the drive with the engine running.
1. Identify the chain size first
The sprocket and chain must belong to the same chain system. 428 chain is common on rental karts, but it is not universal, so do not order from appearance alone.
Check:
- Any markings on the existing chain
- Any markings on the sprocket
- Chain pitch
- Width between the chain inner plates
- The sprocket tooth profile
If you are not certain about the chain, use our guide to identifying rental-kart chain size and length first.
2. Count the teeth
Mark one tooth with a paint pen and count all the way around until you return to it. Do not estimate the tooth count from the sprocket diameter.
The tooth count affects the final drive ratio, so a different sprocket can change acceleration, engine speed and maximum speed. For a straight replacement, record the existing tooth count and compare it with the kart or drivetrain specification.
If you are deliberately changing the gearing, treat that as a setup decision rather than accidentally discovering it after fitting the wrong part.
3. Is it a front or rear sprocket?
The measurements you need depend on where the sprocket is fitted.
Front or output sprocket
The front or output sprocket normally mounts to the clutch, gearbox or reduction-box output shaft.
Record:
- Chain size
- Tooth count
- Shaft or output diameter
- Keyway, spline or other drive arrangement
- Retaining method
- Overall width
- Any offset from the mounting face to the tooth centreline
Rear sprocket
The rear sprocket normally mounts to a carrier or directly around the rear axle assembly. Record the tooth count and chain size first, then identify how the sprocket is mounted.
4. Identify the rear sprocket mounting
Sprocket fitted to a separate carrier
Record:
- Number of mounting holes
- Hole diameter
- Pitch-circle diameter (PCD)
- Centre-hole diameter
- Sprocket thickness
- Tooth count
- Chain size
The carrier itself must also suit the axle diameter and keyway arrangement.
Split sprocket
Some rental-kart systems use a split sprocket that can be fitted without removing the axle. For these, confirm:
- Axle diameter
- Number of sections
- Fixing arrangement
- Tooth count
- Chain size
- Key or carrier arrangement
5. Measure the PCD properly
PCD means pitch-circle diameter: the diameter of the imaginary circle running through the centres of the mounting holes.
Do not measure from the outside edges of the holes and call that the PCD. If two holes sit directly opposite each other, measure centre to centre. For odd-numbered patterns, or where the holes are difficult to reach accurately, use the manufacturer's drawing or a proper PCD measurement method rather than rounding a ruler measurement until it looks familiar.
6. Check sprocket and chain alignment
Before blaming the old sprocket for repeated chain problems, look at how the complete drive is running.
Check for:
- Chain running visibly to one side of the teeth
- Polished wear on one face of the sprocket
- Loose sprocket carrier
- Damaged axle key or keyway
- Bent or distorted carrier
- Excessive sprocket run-out
- Incorrect engine, clutch or gearbox alignment
A fresh sprocket fitted to a misaligned drive normally becomes a fresh worn sprocket.
7. Read the wear on the old sprocket
Replace a sprocket showing:
- Hooked teeth
- Sharply pointed teeth
- Uneven tooth profiles
- Cracks or damaged mounting holes
- Heavy side wear
- Distortion
- Excessive corrosion
- Movement between the sprocket and carrier
Inspect the chain at the same time. A badly worn chain can quickly damage a new sprocket, just as a new chain can suffer when fitted to badly worn sprockets.
Mixed fleets catch people out
Rental fleets evolve. Engines get changed, axles get replaced and carriers get swapped. Karts that started life identical can end up with different drivetrain parts several seasons later.
Do not order a fleet quantity because one kart measured correctly. Check a representative sample first, particularly on an older fleet.
What to send RKP if the sprocket is unknown
Send the Parts Desk:
- Kart make and model
- Approximate year
- Engine and clutch or gearbox type
- Chain marking
- Sprocket tooth count
- Front/output shaft diameter if applicable
- Rear axle diameter
- Mounting-hole count
- PCD
- Centre bore
- Clear photographs of both sides of the sprocket
- A photograph showing how it mounts to the kart
A photograph with a ruler or vernier caliper in shot is considerably more useful than “it’s the normal one”.
Useful RKP links
- Drive Sprockets
- 428 Rear Axle Drive Chains & Sprockets
- How to Identify Rental Kart Chain Size and Length
- How to Measure a Rental Kart Rear Axle Before Ordering
About this guide
Prepared by the RKP Parts Desk and technically reviewed by Jon Symes, drawing on 18 years of rental-kart track, workshop and operations experience.
Need help confirming a part? Send the kart model, measurements and a clear photo to the RKP Parts Desk.