The Southwick hub failure I experienced last month apparently was a
one-off, nobody came forward saying they had, or even heard of a similar
failure. That's certainly good news for the many of us still running
original Southwick hubs on the track.
I engaged the best experts I know, took many pictures for my preliminary
writeup, added a second page of pictures as more questions came up,
(linked at the bottom of the original page) and here are the
conclusions.
The amount of force required to fracture the 6061 aluminum as mine did
was well beyond what anyone would consider normal stress applied to a
hub. Nobody looked at the pictures and concluded there is an issue with
the design or the material choice of the original hubs. Nobody saw
evidence that the material my hub was turned from had any casting
imperfections.
The biggest question we had was whether I experienced a sudden,
catastrophic failure, or did the hub crack as the result of some shunt
and as I put more cycles of stress on the hub the crack propagated to
the point of failure? If the former, there is not much anybody can do as
no telltale signs of an impending failure would be evident. If the
latter, at least in theory crack checking could show if a hub was sound
or needed replacing.
We concluded the fracture was not sudden and catastrophic. As 6061
aluminum has a yield strength of about 45,000 psi, and given the fact
the entire surface area of the fracture is somewhere between 3 and 4
square inches, the force required for a sudden fracture would be quite
large. Additionally, keep in mind that other parts (vertical link, axle,
etc.) would have bent well before the hub saw anything near the force
required for a sudden fracture. Supporting that theory is the fact there
must be hundreds of these hubs on track since they were developed in
2001, and many of them are run with tires with more grip than my
Speedsters.
We now believe I had some incident at some point that did create a
crack, and over time that crack propagated until the failure. I don't
remember any recent incident that could have stressed the hub.
So what to do going forward if you are running the Southwick aluminum
hubs? Checking your hubs for cracks seems to make sense, but it is
necessary to remove the inner bearing race to inspect the inner
circumference of the failure area. The pocket the inner race sits in is
a tight press fit, and while there should be no issue with the
occasional removal and reinstallation of the race, we question how many
times you can perform the R&R of the race without further stressing the
area we are concerned with.
What follows is the conclusions we made. All your typical disclaimers
apply, racing is dangerous, nobody else is responsible for what happens
to you if you heed or ignore any recommendations, etc.
We reached the conclusion that it only makes sense to pull the race out
for a dye penetrant test if the hub is subjected to some big stresser.
Perhaps it has taken a hit during an accident, or even a bad off that
the suspension pounded the bump stop. For a street car, my take would be
if you hit a good pothole really hard. If someone was doing a routine
bearing change and removed the race to replace it with new, obviously
that would be the time to test for cracks. But if the hub has not been
subjected to a big stress event, it is probably best to leave it alone.
Routinely performing a R&R on the inner race may be detrimental in the
long run.
Or, as stated before, GoodParts now manufactures these hubs from 7075
aluminum and has modified the design somewhat with an eye to make them
even stronger. These are on my TR250 now.
I have put the broken hub and bits are in the race trailer, anybody who
cares to see it and render an opinion on what happened is welcome to.
The story may continue to evolve.
My thanks to Chuck Gee, Glen Efinger and Richard Good for offering their
time and expertise here.
We are running the Lime Rock Historics this weekend, getting all our
ducks in a row for the 2025 Kastner Cup one year for now! Stay tuned for
more info on that!
Cheers
Henry Frye
2025 Kastner Cup Co-Chair
On 2024-08-04 13:35, yellow04 via Fot wrote:
> I am throwing this out there as a public service announcement, I broke
> a part that I thought we had bulletproof solution to. At PittRace last
> weekend I broke one of Southwick's aluminum front hubs. The area of
> the hub that the inner race presses into sheared off, thankfully the
> wheel was retained by the outer bearing and stayed on the car. I don't
> know for how many laps that would have been the case!
>
> Has anybody else heard of one of these hubs failing?
>
> Discussions with Richard Good, who took over manufacturing these hubs
> revealed his hubs are turned from a stronger material, the GoodParts
> hubs are made from 7075 T6 aluminum, while Southwick made theirs from
> 6061 T6. Yes, it is a little heavier, but the GoodParts hub is still
> about a pound lighter than stock. If you are unsure where your hubs
> were made, I provided details in the writeup.
>
> I have also been in contact with Chuck Gee, our resident metallurgist.
> He is suggesting anybody running these Southwick hubs should start a
> program of dye penetration testing.
>
> Pictures and writeup here.
>
> https://tr250racer.com/southwick-front-hub-failure/
>
> Hope this helps everybody keep the shiny side up!
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