Chassis Failure

[Glenn B.]

I was running my RCR Lola at a track day at the Circuit of the Americas on July the 5th. Under braking up the front straight entering turn one, the right rear control arm mount tore out of the chassis causing a severe toe-out on that wheel sending the car into a slide. I brought it to a safe stop off track. The car was running Dunlop Vintage hard compound bias-ply treaded tires, not a full slick, so the braking stresses were not extraordinary. My telemetry was showing 1.1-1.2gs average braking force around the track.

You can see in the attached pictures that the pressure on the area caused the aluminum sheet around the mount to distort before the weld failed. This chassis has 2,000 road miles on it and a total of 60 laps at COTA completed at 3 track events prior to the failure.

I am posting this for informational purposes only. I waited to see if the manufacturer would provide the information and specific recommendations to the owners of these chassis. I felt an obligation, in the absence of any notice, to recommend that all owners have these locations inspected and crack checked periodically.

 

[Howard Jones]

Is that a trailing arm mount?

 

[Jac Mac]

double post

 

[Jac Mac]

This bit

 

[Fran Hall RCR]

Glenn
Thank you for posting
As you and I discussed via emails our recommendation is to install two 3/8th bolts through the lower rear transom panel into the radius rod structure
Both upper and lower radius rods are joined as part of a substructure and the two bolts will more than suffice.
This will prevent any potential for aft movement
There is a welded seam inside the chassis that joins the two structures I am mentioning.

 

[Dave]

Hmmm thats a worry.....

 

[Fran Hall RCR]

Dave
With these fasteners installed any concern can be removed
We have recommended this addition in the past as far back as dean lampe track car from memory.
Obviously a car used on track with softer tyres sees much higher loads and higher duty cycle than a street car but these additional bolts even on a street car wouldn't be a bad idea if one is concerned.

 

[Terry Oxandale]

Large washers may be beneficial in distributing the head load on the aluminum for the two bolts as well.

 

[Scott]

Fran,
Thanks for posting the pic. At least its easy to get to with the seats out and the access panels off. Scott

 

[mahlon]

Thanks for posting Glenn! We are running 335/35/17 slicks on our mk-2 and just got back from an event without any problems. We will do a close inspection of the area and make the modifications Fran has suggested. This is the first I have heard of this occurring and is a big benefit to the forum for those of us with this chassis.............................m:stunned:

 

[Glenn B.]

Fran and I have already been back and forth on this.

My race support shop does not agree that two bolts through the seat back is an apprpriate fix. It may stop the twist and stretch on the control arm fulcrum point, but it also creates an impact stress point directly into the back of the driver's seat. A hit from behind or going off backwards into a barrier will transfer the impact force through the suspension directly to the driver's back.

We will have to completely disassemble the rear of the car to cut and re-weld the chassis, so our intention will be to redesign the control arm mounting structures out of steel and to eliminate the transfer of impact force into the cockpit.

 

[Fran Hall RCR]

Glenn
If you manufacture the mounts out of steel surely you will then be bolting these mounts to the aluminum.
All radius rod style suspension cars share the same issue of cockpit intrusion
If you make a cap out if steel that bolts to the top of the radius rod mount it will prevent intrusion do long as the impact allows the link to maintain the same tragectory
It will not prevent intrusion if the rod end breaks and the link gets free

This is a perennial problem , just like having fuel tanks either side of the cockpit
Risks can be minimized but not eradicated


I look forward to seeing what you come up with !

When I get back to my PC I will post a video of a very scary crash involving one of our t70 spider race cars.... The chassis survived intact ,straight and is actually still being raced in South Africa.
The driver was unhurt too.

 

[Pat]

Glenn, if your shop is considering a redesign for your T70, the original GT40 mount looks pretty stout and perhaps provides some useful thoughts for your repair. Here is how the original '40s looked, the pics are from Gelscoe and the restoration of one of the originals. Seems their angled and integrated structure looks like it could handle a lot more of a load. It appears the original T70 utilized a similar structure (third pic) as well.

 

[Fran Hall RCR]

Veek
The structure we have is very similar
The original chassis you picture have failures in the same area and do not change the fact that the radius rods can penetrate the cockpit very easily
Both the chassis you show have very thin material and were designed to be throw away race cars
I have original t70 chassis at the shop and they are not as strong as you may think

 

[Russell]

Not being an engineer and always having to `figure out loads` my thoughts are that the structure is to tall meaning that leverage comes into play. There appears no reason why that set of mounts could not have a longer base perhaps with a thickener pad...this would cut back the leverage issues?
Russell

 

[Fran Hall RCR]

Double post

 

[Fran Hall RCR]

Russel
The upper and lower link locations dictate the suspension geometry and cannot be arbitrarily spaced
The mount is very strong in and of itself.
The additions I mention are a belt and braces addition and certainly take care of any movement
We have raced these chassis in competition for years without any major issues.
As is the nature with anything from garden spades to space shuttles , eventually something will show up . It does not necessarily mean there is a major issue.
It's part of any and every products life cycle
We will gladly talk with anyone that has any concerns and help put them at ease with anything we can

 

[Robert May Eng.]

I was running my RCR Lola at a track day at the Circuit of the Americas on July the 5th. Under braking up the front straight entering turn one, the right rear control arm mount tore out of the chassis causing a severe toe-out on that wheel sending the car into a slide. I brought it to a safe stop off track. The car was running Dunlop Vintage hard compound bias-ply treaded tires, not a full slick, so the braking stresses were not extraordinary. My telemetry was showing 1.1-1.2gs average braking force around the track.

You can see in the attached pictures that the pressure on the area caused the aluminum sheet around the mount to distort before the weld failed. This chassis has 2,000 road miles on it and a total of 60 laps at COTA completed at 3 track events prior to the failure.

I am posting this for informational purposes only. I waited to see if the manufacturer would provide the information and specific recommendations to the owners of these chassis. I felt an obligation, in the absence of any notice, to recommend that all owners have these locations inspected and crack checked periodically.

It does look to me that the column has become detached at the bottom first which has caused the top to tear out.

Bob

 

[Jac Mac]

It does look to me that the column has become detached at the bottom first which has caused the top to tear out.

Bob

Unless there are more substantial welds unseen these two tacks wouldn't hold much...

 

[Robert May Eng.]

Unless there are more substantial welds unseen these two tacks wouldn't hold much...

Its all supposition but I am assuming the turret passes through the deck and its function is to anchor both upper and lower control arms. The lower arm will be pulling the turret backwards under braking and the upper will be pushing it forward. I just wondered if the lower welds have failed under braking causing the turret to tip forward.

Bob