That's a bearing failure I haven't seen before.

This came off my son's Fiero. I haven't seen one break like this before.

I asked him how many curbs he had hit. 

I'm wondering if the axle nut was loose.

One of my many Neon race car hub failures was very much like that.

The glory of racing a Neon.  You get to see all sorts of hub failures.

The good thing is it's fairly easy to change. 

The more I think about it, the axle nut wasn't tight enough. That's the only way I can see that failure happening. It's supposed to be torqued to 200 ft-lb. If it's not then all the load on the flange is picked up by the stub without any assistance from the axle shaft itself. 

I had that happen on our first Lemons Civic, huh sheared right off from the bearing, car came in with the brake rotor holding the wheel on.  Swapping to Integra knuckles with larger hubs/bearing solved that problem. 

Had that happen in my Focus track car.   The multi piece axle nut came apart and broke the hub.  It didnt make a single sound when it happened.  I ran a lap an a half at Pocono before I had to come in.  I was losing brake pedal,  A couple pumps and brakes were back.  The rotor was flopping around pushing out the pads.  Everything felt normal otherwise, full power, not a sound out of it.   I noticed something was wrong when I jacked up the car and the wheel flopped over a bit. 

After doing some digging, the Fiero has a problem with aftermarket hubs failing and the OE hubs are NLA. 

Modified J-body hubs are one option (Edit: They recommend starting with OEM rather than aftermarket as well):

https://www.fiero.nl/forum/Forum2/HTML/134524.html

This guy sells custom rebuildable hubs but they're not cheap and "not for racing:"

http://rodneydickman.com/product_info.php?products_id=427

The W41 cars (Calais and Achieva SCX) were notorious for failing bearings, my Achieva had that exact failure on one front hub. 

I don't know if this works on the Fiero, but the racers used to put the big car (Bonneville FWD and similar) hubs on their cars. Bolt pattern is different though.

cfvwtuner said:

Had that happen in my Focus track car.   The multi piece axle nut came apart and broke the hub.  It didnt make a single sound when it happened.  I ran a lap an a half at Pocono before I had to come in.  I was losing brake pedal,  A couple pumps and brakes were back.  The rotor was flopping around pushing out the pads.  Everything felt normal otherwise, full power, not a sound out of it.   I noticed something was wrong when I jacked up the car and the wheel flopped over a bit. 

I had a similar failure on the Jeep at one point, but it happened on the highway.  In my case, the axle nut was still pinned in place, etc. so it hadn't backed off.  But it looked like the actual bearing pretty much shredded internally, leaving a ton of play.  The scary part was the lack of any funny noise.  It was fine at my last stop ~2 hours from home.  Getting off the highway at the end of the drive, I hardly had any brake pedal until I pumped it.  Got it home and it had significant extra camber on that wheel (which knocked the pads back) and tons of play in the bearing.  The hub and bearing came out in pieces when I replaced it and I never did find some of the bearing balls.