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I'm not an expert on these cars, but I'm seeing something different from the pics.
The inside sidewall of the tire is completely trashed. If the suspension failed, I would have thought it would have unloaded the tire and then when the driver hit the brakes, it would have locked the tire (like the observer stated). I would not have expected the sidewall of the tire to be destroyed.
Maybe the earlier repair was no good and it slowly cut down the sidewall. Then a slow leak developed and that impacted the handling. Finally the whole tired failed and that started the accident.
Just my $0.02.
A couple of other folks who examined the wreckage thought it was something that carved out the sidewall on the inside of the tire that caused it.
With all the damage to that wheel as a result of the accident (especially since it was torn from the car), it may be difficult to distinguish which damage occurred to the tire before the impact vs. as a result of the impact ...
With all the damage to that wheel as a result of the accident (especially since it was torn from the car), it may be difficult to distinguish which damage occurred to the tire before the impact vs. as a result of the impact ...
Yes, agreed. I seem to want answers more than anyone else in this case (ironically even more than the owner of the car I think), but I might have to expect that we may never know exactly what happened.
I just want to make sure this doesn't happen again, and figure out what steps would take differently next time. (More shakedown time, more inspection time, be more mindful of pitting right away at first sign of something wrong.)
The tire idea is interesting, but the whole sidewall? A broken suspension bit in the sidewall while rotating would do that.
FWIW, the eyewitness account earlier does not seem to support a flat/tire failure:
I witnessed the accident.
It appeared to me something failed on the driver's side rear suspension. That corner of the car "fell down" and pinched the tire on that side to where it was not rotating. I believe the driver hit the brakes immediately. 3 corners of the car tried to slow. The damaged corner did not.
One thing is certain, without access to at least photos of the underside of the car showing the subframe, trailing arm pockets, and inner suspension points, you will not be able to figure this out. Even with all that, you still may have a very hard time. Stuff happens on the race track.
Upon a second look of the pictures I noticed a few things. First off, the front half of the lower rear control arm is still on the car, so the pocket did not depart the car, so this is not the cause:
Second, it looks like the lower control arm is there, and may have parted. Looking back at the wheel, the only attachment point that is not broken appears to be from the lower control arm. If one thinks of it, the suspension piece that breaks no long has tension on it. It is the other suspension pieces that take a beating while the detached piece flails around, possibly diggiing into the inside sidewall of the tire. Here is that pic annotated:
A common upgrade for these cars are adjustable lower control arms. The length of these is adjusted with threads that work like a turnbuckle with a jamb nut. From those pics, it looks like the lower control arm separated at the outer threaded joint. The way to know for sure is examine that point on the tire and the car closely - did it sheer off or pull apart?
From what I can see here, I'm concluding the lower control arm separated. Note the separation point is not the outer lower ball joint. It looks like the separation happened at the outer lower control arm length adjustment mechanism.
Further, if the joint was unthreading, the left rear camber would get more negative and the rear toe would change as well. These cars are very sensitive to rear alignment - this could be what you were feeling before it let go.
From that second set of pics, it is clear the rear trailing arm pocket did not fail. It is bent up from the forces, but it is still attached.
A close inspection of the wheel as shown may help:
This photo is very interesting:
Missing from the pic above is a clear view of the upper control inside attachment point. I think that may be the upper control arm dangling there. The spring perch may also be missing. If it is, that could be the cause, or could have been torn off in the mayhem. The upper perch is the bottom of the unibody. Just spitballing, but could the spring have just popped out? Was there a bang before the spin/impact? A popped spring would make a lot of noise, however, if just the spring departed I wouldn't expect so much damage.
I don't think the subframe failed from those pics unless the upper control arm inside anchor point separated, can't tell from the pics.
One thing I do know: there have been aftermarket adjustable lower control arms that have had issues and even those that don't can still fail if that jamb nut is not tight. I'm going to add checking that nut to my pre-track inspection routine.
IMHO, the tire's inside sidewall damage also points to a failed lower control arm.
This picture is interesting too and may point to the upper control arm inside attachment point at the subframe. The upper control arm is long, about 2ft, so a lot of it is missing. If there is still a chunk attached at the inner tie point, it may not have failed.
It would not surprise me if a lot of E36s and E46s are running Bimmerworld adjustable lower control arms. Bimmerworld is a long time and reliable BMW supplier.
IMHO it is down to:
1) Lower control arm failure.
2) Upper control arm attachment/subframe failure.
3) Both the upper or lower control arms could have cut the inside of the tire. However, I highly doubt the upper control arm just failed as I've never heard of it and if it failed at the inside connection, it could not have cut the tire. The tire evidence still points to the lower control arm.
4) From your OP, the car had been involved in a number of offs. If these were hard, they could have cracked something, like maybe the lower control arm. In looking at these pics, it does not appear the lower control arm separated at the thread point, negating the theory of it unscrewing. However, it does appear to have failed at its weakest point (it is hard to tell from the pics). May have happened in the following crash, or may have have been cracked if the car was spun sideways into a curb, hole, or other obstruction.
5) The change in handling just prior to the incident indicates something was working loose which points to a crack opening up or a bolt backing out. The upper control arms in these cars are aluminum - I have a hard time believing they would flex long enough at a crack for you to feel it. If the upper control arm failed, I would expect it just to snap with zero warning and, again, they don't have a reputation for doing this. I'd be really curious if the upper control arm bolt is still in the subframe.
It may be worth a phone call to Bimmerworld and/or Turner Motorsport and ask them as they are suspension experts on these cars with lots of racing experience.
I'm still taking "lower control arm failure for $500 Alex", but I'd also really like to know what the inside of the upper control arm looks like.
I'm curios if what is circled below is the inside half of the upper control arm. The spring would have been above it. If it is, then none of the inside joints or anchor points completely let go, which means it was unlikely a subframe failure.
One thing to take home from this thread is that thorough "nut and bolt" checks by a knowledgeable mechanic before races/events are insurance well worth paying, even for folks who do most of the maintenance work themselves.
One thing to take home from this thread is that thorough "nut and bolt" checks by a knowledgeable mechanic before races/events are insurance well worth paying, even for folks who do most of the maintenance work themselves.
Yeah the car just spent a month at the mechanic after the last race since the owner had crashed the front end. Part of the suspicion here is that something was missed while it was there, though I would give them the benefit of the doubt as they are a good shop with a lot of experience with race cars.
11-03-2018, 02:06 PM
