How to Choose a  Rear Axle Setup for a Cyclekart

A good rear axle setup is one of the most important parts of a cyclekart build. It affects how the kart drives, how easy it is to assemble, how reliable it is, and how simple it will be to maintain later.

For most Australian cyclekart builds, a 25mm rear axle is a practical and proven choice. It gives you a good balance of strength, availability, simplicity, and compatibility with common go-kart and custom fabrication parts. There are a multitude of options ranging from 25-40mm and no size is infinitely better than the others. Choose a size that suits your budget and what parts are available. Remember, the best cyclekart is a built one.

For me, a solid 25mm axle is the best blend of strength, cost and parts availability. 

This guide explains the main parts of a 25mm rear axle setup and what to look for when choosing parts for your cyclekart.

Why 25mm Is a Good Size for Cyclekarts

Cyclekarts are lightweight machines, powered by a GX200-style engine or similar clone engine. They do not need the same heavy rear axle hardware as a full-size race kart, but they still need parts that are strong, straight, and easy to mount.

A 25mm axle is popular because it is:

• Strong enough for typical cyclekart use
• Easy to support with common pillow block bearings
• Compatible with readily available hubs, collars, sprocket carriers, and brake components
• Simple to fabricate around
• Well suited to home-built and kit-built cyclekart chassis designs

A well-planned 25mm axle setup also makes the rest of the build easier, because your wheels, sprocket, brake disc, bearings, and hubs can all be selected around the same shaft size.

The Main Parts of a 25mm Rear Axle Setup

A complete rear axle assembly usually includes:

• 25mm rear axle shaft
• Pillow block bearings
• Bearing mounting plates or chassis brackets
• Wheel hubs
• Sprocket carrier
• Rear sprocket
• Brake disc or brake hub
• Shaft collars
• Key steel
• Wheel adapters, if required
• Spacers and fasteners

The key is to make sure all of these parts are compatible with each other before you start welding brackets, cutting spacers, or drilling holes.

1. The Axle Shaft

The axle shaft is the foundation of the whole rear assembly.

For a cyclekart, a 25mm axle with a 6mm keyway is a very practical and the most common option. The keyway allows the wheel hubs, sprocket carrier, and brake components to be locked to the axle so they rotate with it.

When choosing an axle, check:

• Shaft diameter: 25mm
• Keyway size: commonly 6mm
• Overall length
• Material and finish
• Straightness
• Whether the ends need machining, drilling, or retaining hardware

The axle should be long enough to suit your desired rear track width, wheel offset, bearing positions, and hub arrangement. It is worth laying the entire assembly out before cutting or finalising anything.

2. Bearings and Bearing Mounts

Most 25mm cyclekart axle setups use pillow block or flange-style bearings.

Common options include:

• UCP205-16 pillow block bearings
• UCFL205-16 flange bearings

For CSC parts, the important detail is that these parts are supplied to suit a 25mm bore, not 25.4mm/ 1inch bore. That means they are suited to a 25mm metric axle. 0.4mm may not sound like much, but trust me, its enough to cause trouble. I learnt the hard way in my first build. I used a a 1 inch sprocket carrier on a metric axle and it would creep in position and would spit the chain frequently. Tighten as you might, it was never enough to stay in place

Bearing selection matters because the bearings support the axle and keep it aligned. Poor alignment can cause drag, chain issues, vibration, and premature wear.

When setting up your bearings:

• Keep both bearings square to the axle
• Mount them on strong, flat surfaces
• Avoid forcing the axle through misaligned bearings
• Make sure the bearing locking screws are accessible
• Leave room for collars and adjustment

A simple, strong bearing mount is usually better than an overcomplicated one.

3. Wheel Hubs

Wheel hubs connect your rear wheels to the axle.

For cyclekart use, 25mm hubs are commonly used with either:

• M8 studs
• M8 threaded holes

CSC 25mm hubs are designed around a 25mm axle and a 6mm keyway, with a 3 x 50 PCD mounting pattern. This makes them suitable for cyclekart and go-kart style applications, depending on the wheel and adapter arrangement.

When choosing hubs, check:

• Bore size: 25mm
• Keyway size: 6mm
• Mounting pattern
• Stud or threaded-hole arrangement
• Hub length
• Material
• Finish
• Compatibility with your wheel or adapter

For many cyclekart builds, wheel adapters are used to connect pit bike or motorcycle-style wheels to go-kart hubs. This is where planning the PCD, wheel offset, and spacer stack becomes important.

Whilst they look small, a 25mm hub with an adapter set to suit pit bike wheels is a tried and tested method worldwide, being in use for many years to great success. The main failure point of these Pit Bike wheels is not the mounting or hub, but the spokes. Cheap wheels are often supplied with loose spokes which can't hold up to the lateral forces on the wheel and quite often leads to catastrophic failure

4. Sprocket Carrier and Rear Sprocket

The sprocket carrier locks the rear sprocket to the axle. This is what transfers drive from the engine and clutch or torque converter to the rear axle.

Before choosing the sprocket, decide what chain pitch you are using. Common small-engine cyclekart setups often use #35 chain, but you should always match the chain, clutch, sprocket, and sprocket carrier as a system.

For example, a 61T sprocket for #35 chain needs to be used with matching #35 chain and a compatible front sprocket or torque converter output.

When selecting sprocket parts, check:

• Chain pitch
• Tooth count
• Mounting pattern
• Centre bore
• Carrier bore
• Keyway size
• Alignment with the engine drive sprocket

Chain alignment is critical. The front and rear sprockets need to run in the same plane. If the chain is offset or twisted, it will wear quickly and may derail.

The most common ratio is somewhere between 6 and 6.5:1. So for a #35 Chain you would use the Tav 2 10 tooth sprocket on your torque converter and a 60-65 tooth sprocket on your axle. For those using 420 Chain you would pair the 12T Sprocket on your torque converter to a 72-75T sprocket on your axle

5. Rear Brake Setup

Most cyclekarts use a rear brake setup mounted to the axle. This usually includes a brake disc, brake hub or carrier, caliper, and master cylinder.

When planning the brake, make sure there is enough room for:

• Brake disc
• Caliper
• Caliper mount
• Sprocket and chain
• Bearings
• Wheel hubs
• Shaft collars
• Chassis rails

The brake disc needs to run true, and the caliper must be mounted firmly. A flexible or poorly aligned caliper bracket can cause poor brake feel, uneven wear, and reduced stopping performance.

For a simple cyclekart build, a single rear hydraulic brake is common. The final arrangement should always be checked carefully before driving.

Remember to stay within Australian guidelines, only rear brakes are permitted! Also a hand brake is also a must have requirement. The CSC Brake caliper is both a hydraulic caliper and handbrake in one unit and is a perfect and simple way to comply with the Australian Rules

6. Shaft Collars, Spacers and Key Steel

Small parts make a big difference in a rear axle setup.

Shaft collars are used to locate components on the axle and prevent side movement. Spacers may be required to position wheels, sprockets, bearings, or brake components correctly. Key steel locks rotating parts to the axle.

You will usually need to think about:

• Bearing position
• Hub position
• Wheel spacing
• Sprocket alignment
• Brake disc alignment
• Side clearance to the chassis
• Chain clearance
• Tyre clearance

Do not rely on grub screws alone to handle every load. A good setup uses the keyway for drive, collars or shoulders for location, and proper fasteners for clamping.

7. Live Axle or One-Wheel Drive?

Many cyclekarts use a live rear axle, where both rear wheels are fixed to the axle and rotate together.

This is simple, strong, and easy to build. The trade-off is that both rear wheels turn at the same speed, which can make tight low-speed turning slightly heavier compared with a differential setup.

Most people cite turning circle as a reason to not use a live axle set-up but I have personally never found an issue. I can easily do a U-Turn on a suburban street with no issue. Keep in mind also, that on a Single wheel drive, if you lift the driven wheel, your axle mounted brakes are not going to do anything at all.

For most cyclekart use, a live axle is a practical and reliable choice. It keeps the build simple and uses parts that are easy to understand, inspect, and replace.

8. Check Your Rear Track Width

Before buying or fitting axle parts, decide on your rear track width. The Australian regulations dictate a a maximum track width of 1 metre centre to centre.

The rear track is affected by:

• Axle length
• Wheel offset
• Hub length
• Adapter thickness
• Bearing position
• Chassis width
• Spacer arrangement

It is worth mocking up the rear end before final welding. Even a simple bench layout can help you avoid surprises.

Check that the tyres clear the chassis, the chain has a clear path, the brake caliper has enough room, and the wheels sit where you expect them to.

9. Match the Whole System, Not Just One Part

A common mistake is choosing one part in isolation.

For example, a sprocket might suit your chain, but not your carrier. A hub might suit your axle, but not your wheel. A bearing might suit your axle, but not your chassis bracket.

A good rear axle setup should be chosen as a complete system:

• Axle matches bearings
• Bearings suit the chassis mounts
• Hubs suit the axle and wheels
• Sprocket carrier suits the axle and sprocket
• Chain pitch matches the engine drive sprocket
• Brake disc and caliper fit within the available space
• Collars and spacers lock everything into position

Taking the time to match these parts properly will save a lot of frustration later.

Suggested Basic 25mm Cyclekart Rear Axle Setup

A practical starting point for many cyclekart builds would include:

• 25mm keyed rear axle
• Pair of 25mm bore pillow block bearings
• Pair of 25mm wheel hubs
• Sprocket carrier
• Rear sprocket to suit your chain pitch
• Rear brake disc and caliper setup
• Shaft collars
• 6mm key steel
• Wheel adapters, if using pit bike or motorcycle-style wheels
• Suitable fasteners and spacers

The exact parts will depend on your chassis design, wheel choice, engine setup, and preferred layout.

Final Thoughts

A 25mm rear axle setup is a solid choice for a cyclekart. It is strong enough for the job, easy to work with, and compatible with a wide range of useful parts.

The most important thing is to plan the rear end as a complete assembly. Think about the axle, bearings, hubs, sprocket, brake, wheels, collars, and spacers together before committing to final positions.

A tidy rear axle setup makes the whole cyclekart easier to build, easier to maintain, and more enjoyable to drive.

Cyclekart Supply Co. stocks a growing range of 25mm axle components, hubs, bearings, sprockets, collars, and related parts suitable for Australian cyclekart builders.