Failure Points: NA Miata Front Wheel Bearing

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The harsh environment of the racetrack pushes a car right to its limit and beyond. As such, racecar failures are bound to happen in many different ways. Failure Points is a new series that dissects these moments and what to do when things go wrong. This time it is the front wheel bearing of the Super Touring 6 NA Miata.

Failure Point Analysis

Often times, failures are abrupt, and this was no exception. During race 3 at the recent NOLA Motorsports Park event, the front wheel bearing failed on entry to turn 5. In the video below at the 12:10 mark the bearing lets go. And as you can see, I originally suspected a front caliper issue.

In the driver’s seat, what I felt was the engine bog/drag, and then the car understeer unexpectedly. It was akin to a brake dragging and when I started to accelerate again, I felt an intermittent sensation similar to anti-lock brake activation. Only problem, I was no longer in a braking zone and my car does not have ABS. I exited the track, using the access in the esses to limp back to pit and retire the car.

Initially, I suspected the front caliper as I had no previous warnings of bearing failure. This was compounded by the burning smell as the caliper was coated in tire rubber that was melting, and consequently glazing the rotor.

Closeup of the NA Miata front right caliper with tire rubber melting onto the rotor.
The excess rubber in the wheel started melting onto the rotor. Initially pointing me to the caliper.

It is easy to see how the brakes were my initial diagnosis. Typically, bearings that are failing tend to produce noise and exhibit play and that was not the case here. However, as I removed the wheel, caliper, and rotor, the failed wheel bearing became evident. It would spin freely briefly and then lock up. This is what was giving me the ABS sensation, causing the understeer, and introducing a ton of rubber into the wheel and on the caliper.

Crushed ball bearings from the NA Miata racecar wheel bearing.
Some of the ball bearings from the wheel bearing are not like the others.

Failure Point Resolution

Resolution of a failed wheel bearing is replacement. It is extremely easy on the Miata, and I document the process here (link tomorrow I promise).

And part of failure resolution is avoidance. On Miata racecars, front wheel bearing failures are not rare. They may show symptoms such as grinding, wiggling, and vibration before failure, but they can also be more extreme than my case. Abrupt failures can compromise the spindle the bearing sits on and if the spindle snaps, the wheel goes with it. This can be catastrophic at speed.

To avoid any potential front wheel bearing issues on the NA Miata moving forward, I am viewing the bearing as a wear item and will most likely replace them every season. I will also have a bearing added to my spares kit.

By Chris Simmons

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