Quick answer: To identify a rental-kart rear axle, measure the outside diameter, overall length, construction and every keyway or locating feature. “30 mm axle” is only one measurement; length, keyway size, component positions and end details can still make the replacement wrong.
Safety: A rear axle carries wheels, brake and drive components. If it is cracked, badly bent or has damaged retaining features, keep the kart out of service until a competent mechanic has assessed it.
The measurements that matter
- Outside diameter: measure on a clean, unworn section with a vernier caliper. Check more than one position.
- Overall length: measure end to end along the centreline, not around the curve of a bent axle.
- Solid or hollow: record the construction and, for a hollow axle, the wall thickness where it can be measured safely.
- Keyway size: record width, depth and usable length. Common-looking 6 mm and 8 mm systems are not interchangeable.
- Keyway positions: measure from a consistent axle end to the start and finish of every keyway.
- Bearing positions: record bearing references, locking style and the centre-to-centre position of the chassis carriers.
- End details: photograph threads, circlip grooves, cross-drilled holes, steps, tapers and any welded or pressed features.
Measure the associated components too
An axle rarely works alone. Record the bore and keyway of the wheel hubs, brake-disc carrier and sprocket carrier. For the drive, also record sprocket PCD and chain type. For the brake, record disc diameter, thickness and fixing pattern. This catches mixed fleets where two karts look alike but have different hardware.
Checking whether the old axle is a reliable template
Rotate the axle and watch a fixed reference point near the centre and both ends. If it visibly runs out, do not use a single measurement from the bent area as the nominal specification. Inspect the bearing seats, keyways and retaining features for fretting, cracks, burrs or previous repair work.
A straight replacement will not cure repeated bearing or tyre problems if the chassis carriers, hubs or associated components are misaligned or damaged.
Useful RKP reference points
- 30 × 900 mm solid rear axle with 6 mm keyway
- 30 mm and 50 mm sprocket-carrier options
- 6 × 6 mm axle keyways
- 8 × 7 mm axle keys in 40 mm and 50 mm lengths
- 30 mm brake-disc carrier with 115 mm PCD
- 30 mm axle bearing holder with UC206 bearing
These examples show why diameter alone is insufficient. Match all dimensions and fitted components before ordering.
The photo and measurement pack to send RKP
- Kart make, model and approximate year
- Axle diameter and overall length
- Solid or hollow construction
- Keyway width, length and position
- Bearing references and carrier spacing
- Hub, sprocket-carrier and disc-carrier bores
- Full-width photograph plus close-ups of both ends and all keyways
Further reference
- RiMO user and maintenance manual – useful historical model reference; verify applicability to the exact kart and year.
- HSE guidance on inspection of work equipment – inspection frequency should reflect risk, manufacturer recommendations and actual operating conditions.
Reviewed 25 August 2026. This is an identification guide, not a substitute for the kart manufacturer’s maintenance procedure.