Kart chassis setup has endless tuning possibilities, with wheel hubs being one key component often overlooked.

Hubs connect the wheels to the axles and their design characteristics including length, material, and interface shape impact performance.

Tuning hubs, along with axle stiffness, provide an effective way to adjust grip at both ends of the kart. Understanding hub dynamics helps optimize handling balance.

Rear Hubs - Balancing Rotation and Forward Bite

Rear hub length is a common tuning adjustment, with longer hubs typically increasing rear grip.

The added hub material over the axle acts somewhat like a stiffer axle, reducing flex and allowing more rear tire bite.

This helps acceleration, but too much rear grip hinders rotation as the kart wants to drive straight rather than turn. Finding the ideal compromise is key.

On narrower axles like 30 and 40mm, hub length has a very noticeable impact on rear grip and handling balance.

The softer axles flex easier, so added hub stiffness makes a big difference.

Classes like Yamaha or Briggs LO206 with 30mm axles can utilize hub length to fine-tune rotation versus forward traction.

But on the predominant 50mm axles, hub length has a diminished effect. The stiff 50mm axle diameter reduces flex, meaning the hub provides less relative additional stiffness.

At this width, changing the hub length may only provide subtle handling tweaks. More impactful can be actually cutting the 50mm axle to reduce stiffness. This allows the hub to take up more flex, amplifying its effect.

Cutting or swapping to pre-shortened axles delivers more dramatic results than just changing hub length.

For example, cutting 5mm off each axle end concentrates the hub's leverage onto a smaller section, increasing flex and freeing up the chassis.

When making big changes it's better to modify the axle itself. Save small hub length changes for minor adjustments.

Up Front - Adding Grip for Speed

Front hub length follows the same principles - longer hubs equal more grip - but here added grip is usually desirable.

Within reason, the front grip promotes quicker turn-in and helps the kart arc through corners. Hubs around 70-80mm provide a good starting point for top-level racers.

In lower power classes, too much front grip actually hinders performance by reducing chassis roll-off.

So sportsman-level karts often run minimal front hubs around 40-50mm combined with narrow 17mm spindles and flex discs.

This keeps the front free for responsive turning.

Conversely, in high downforce and power classes like shifters, huge 90-100mm hubs are common to ensure the front end stays planted.

At race speeds, a maximal front grip is needed to maintain control.

The demands of the class dictate optimal hub length, with more power and speed requiring longer fronts.

Wet conditions are the other scenario requiring extra front grip.

Rain necessitates longer front hubs, even in lower power karts, to aid turning and prevent understeer.

The slick track means more bite is welcome when turning the wheel.

A "dry" hub around 50mm may need to stretch to 70mm+ in the wet. Adjusting the front hub length helps counterbalance changing grip levels. 

Hub Materials - Heat Management & Strength

Hubs are constructed using either aluminum or magnesium, with each material having different properties affecting performance.

Magnesium is lighter than aluminum, so magnesium hubs reduce rotating mass compared to aluminum.

Many racers believe the magnesium's porous, heat-absorbing nature also helps manage tire temperatures.

The downside is magnesium is approximately 30% weaker than aluminum.

This may contribute to more front hub flex, but likely not enough to noticeably impact handling.

For longevity, aluminum resists cracking better after extended use. Either material works well, so racers can choose based on weight, temperature management preferences, or cost.

Hub-to-Wheel Interface - Maximizing Contact Patch

How the hub contacts the wheel is another design factor.

A full-circle hub centers itself in the wheel and provides maximum surface area contact. This slightly stiffens the overall wheel package.

"Cloverleaf" shaped hubs with cutouts reduce the contact patch but are also lighter.

More important is the hub-to-axle interface.

A tight precision fit between the hub ID and axle provides solid contact and power transfer.

Hubs that are machined with minimal interior contact area isolate stiffness only where the pinch bolt clamps down.

This style converts the hub into a tuned "bushing" for targeted axle flex rather than overall stiffening.

Multiple pinch bolts also increase stiffness, spreading clamping force over a longer section of the axle rather than a single point.

Hubs with 2 or 3 bolts have less tendency to rotate or deflect.

There are always multiple design factors at play, but optimizing the hub-to-axle interface ensures efficiency and tuning potential.

Mastering Hub Tuning

Hubs often don't receive enough credit as a tuning tool.

But like every component, optimizing hub design has a clear impact on handling. Stiffness, grip, and balance can be adjusted through thoughtful hub changes.

Experiment with different lengths and materials at both ends to best match your driving and track conditions.

And remember, hubs work in conjunction with axle design.

Changing both hub and axle attributes compounds the effects.

Don't be afraid to try non-traditional combinations!

As you correlate changes to lap times and behavior, the ideal balance will reveal itself.

Add hub tuning to your toolkit for enhanced adjustability and quicker lap times.