Broken C5 Hubs on the track - Add this check to your pre-race safety check

[FOXBAT]

Wow! What a great post!

While I crawl all over my suspension after every HPDE, I will definitely look at the hubs more carefully. Another thing I do is jack up the chassis and powerwash the undercarriage prior to inspection - a trick I learned from a BMW mechanic. Makes things lots easier to do without all the mess.

[froggy47]

Originally Posted by FOXBAT

Wow! What a great post!

While I crawl all over my suspension after every HPDE, I will definitely look at the hubs more carefully. Another thing I do is jack up the chassis and powerwash the undercarriage prior to inspection - a trick I learned from a BMW mechanic. Makes things lots easier to do without all the mess.

Do you have an outdoor lift? How do you wash without getting a mess on the floor?

[FOXBAT]

The stuff that I wash out is brake dust, rubber marbles, rocks, dirt, etc. All of this is manageable on a garage floor. I just hose it all to one spot, let it dry, and sweep up.

[Spankythegator]

Great video! Thanks!

[ghoffman]

Originally Posted by Subdriver

Oli,
That's ugly... thanks for sharing the video. I did have wheel hub replacement on my annual checklist, but mostly due to rapidly increasing slop in the bearing, not actual failure of the hub.

I wonder if its time to start considering a spec tire in T1. These cars just weren't designed to run the sustained G's capable with the current generation of DOT track tires. I'd like to see us all have to run something like the Toyo RA1 or Nitto's.

I am not 100% sure it is the tire loads alone that is doing this. Oli made the comment that it is always the fronts that fail and considering the cyclic loads that are on the rears with full power then a complete load reversal under braking you can make the argument that the rears see more loading, especially since the rear tires are bigger so they can generate more force. The fronts see more braking load but it is never reversed in sign. I (Brad please jump in here since you know more about heat transfer than most anyone considering gthe big tea kettle that you run in your job), am thinking that this is a heat transfer issue while it is under load. I submit that the front rotors are dumping a tremendous amount of heat in to the front spindles and degrading the material properties to the point that the tire loads are exceeding the fatigue strength of the spindle. At room temperature, the loads are below the yield point, but the elevated temps (especially on the front) put that point below what we are seeing in use. I have an idea on how to test this theory, if anyone is interested.

[Olitho]

Originally Posted by ghoffman

I am not 100% sure it is the tire loads alone that is doing this. Oli made the comment that it is always the fronts that fail and considering the cyclic loads that are on the rears with full power then a complete load reversal under braking you can make the argument that the rears see more loading, especially since the rear tires are bigger so they can generate more force. The fronts see more braking load but it is never reversed in sign. I (Brad please jump in here since you know more about heat transfer than most anyone considering gthe big tea kettle that you run in your job), am thinking that this is a heat transfer issue while it is under load. I submit that the front rotors are dumping a tremendous amount of heat in to the front spindles and degrading the material properties to the point that the tire loads are exceeding the fatigue strength of the spindle. At room temperature, the loads are below the yield point, but the elevated temps (especially on the front) put that point below what we are seeing in use. I have an idea on how to test this theory, if anyone is interested.

Hmmm? That is a plausible theory. How about in addition to the heat that the weight transfer under braking simply transfers much more load to the front hubs than you can ever transfer to the rear under acceleration? The front of my car on static scales is also about 200 lbs heavier. Under braking load I bet I put 2500 lbs up front, plus I am an avid trail-braker so that creates a heavier lateral load....

Fastest regards,

Oli

[ghoffman]

Absolutly true, but it is a combination of both. In any case, reducing the heat input into the bearing is beneficial even if the flange does not fracture. These bearing sets also die from seal and bearing failure and that is almost all due to heat. Call me Oli, I'll fill you in on what we are doing.

[Falcon]

I've had the same issues with front hubs as Oli.

The first indication I got was a sudden and severe case of piston knockback. After going through a turn and braking for the next turn, the brake pedal went almost to the floor. I pulled into the paddock immediately and jacked the car up. Although the bearing felt good, with no slopppiness, when I spun the tire the rotor rubbed on the brake caliper bracket indicating the bearing plane wasn't true. That's when I saw the fracture on the bearing flange.

[Cobra4B]

This type of thing makes me want to step it back a notch for HPDEs and run something less aggressive than a V710 or R6 like I have been.

So many decisioins

[Subdriver]

Gary,
Your assessment is likely on the mark.

I feel like we didn't have these issues 2-4 years ago and tires jumped at me as the biggest change in the last several years. The car hasn't changed that much, but T1 lap records are falling left and right.

I wonder if better tires, coupled with more serious race pads, have increased the heat stresses (better braking grip, higher straightline speed - more heat to generate and dissipate), which combined with higher outright load stresses (better cornering grip), have decreased the fatigue life of the hubs to the point that we are seeing failures like this more often now than several years ago...

or its been happening all along and I just never heard about it.

[ghoffman]

This begs the question of Super Touring reliability. The new ST class for the C6Z has the same bearings and they have 100 more HP, bigger tires, and (hopefully) better brakes. Obviously, competitors in ST need to inspect this more frequently because it is more of the same.
BTW, I submitted a PowerPoint proposal to SCCA Comp board to allow brake changes for the C6Z in ST. The OE calipers are so abysmal that someone is going to get hurt in competition and they need to allow changes to prevent it. People seem to forget that the braking energy goes up as the velocity squared. There is a BIG difference between 160 and 140 when it comes to the heat loading, like 30%. I will have nothing to do with this class if they do not permit a brake change, either as a competitor or supplier.

[ibismojo]

are you allowed to run fabricated spindles in your respective race series?

[Olitho]

Originally Posted by ibismojo

are you allowed to run fabricated spindles in your respective race series?

Not in SCCA T1.

[GR8 WHITE]

That sucks..... I know the feeling! I had my left front g out as well. It was still "driveable" and I sucke dit up for over a year with a slightbuzzing sound when I turned to the right. (Right steer is left side Hub)

So, I checked around and foun dthem from teh PARTS LADY on E bay, brand new for under $400 for two.

Hope that helps out a little.

[OKsweetrides]

What are the hubs made of? Mating surfaces, etc. everything to boot

If it's steel... it's purely from a weak puny alloy, more than likely cast, and then machined. A solid upgrade to forged units, properly reinforced main mating surface and wise thermal coating between rotor hat and hub would work well. As well as low thermally conductive yet high strength studs, like titanium alloy would bode well.

If it's aluminum, then no shock there that it fails like that... I mean seriously, aluminum alloy loses strength ridiculously quick when you start getting things hot and fatigue load things like it's no one business.