Chassis Failure

[Charlie Farley]

Belt & Braces job Fran.
There are inherent fallibilities with old designs....you can only do so much.

 

[Keith]

Can anyone explain why the radius links have to be so long in these designs? I had a 4 link set up in one of my race cars and they were half that length. Mind you, it was a live axle..

 

[Paul W]

Toe is affected more under bump and droop the shorter the arms are.
On a live axle it wouldn't matter.

 

[Keith]

Hey Paul! How's you? Thanks for the reply. How do they deal with it in modern mid engine cars?

 

[Paul W]

Hi Keith, all good here - hope your doing ok.
All to do with having the MacPherson struts - solves a multitude of sins on a road car.
Obviously it will differ from car to car but comparing the 40 to my Boxster.
There is still the lower arm but the top one isn't needed as the strut top is fixed to the body.
This means the lower arm is mounted at floor level out of harms way.

 

[Jac Mac]

dwgs showing forces applied to radius rods and a couple of possible ways to strengthen current setup.

 

[Fran Hall RCR]

Thanks for your insight jac

The brackets we already offered spread the load onto another much larger surface area and a plane perpendicular to the mounting surface of the primary turret mount helping to distribute the load down to the floor of the monocoque, larger than even you suggest necessary. This area of the floor also has internal bracing that creates the bulkheads inside the torque box area of the engine bay.

The "new bolt on brace" also create a cap over the top of the turret to help prevent runaway radius rods from cockpit intrusion which the modification done to Craig's chassis do not appear to have. This type of cap/safety option does not appear to be used on many other radius rod suspension style cars, real or replica, obviously an oversight on everyone's behalf , including mine especially in the modern world of more readily available and powerful engines ,stickier tyres and better brakes.

My Lola continuation spyder has a small 0.040 plate closing off the front of original design turret but it is not welded in place , only buck riveted. This is obviously acceptable as a period type modification , but without that the rod would be capable of direct cockpit intrusion with only a fiberglass bulkhead as protection .

The RCR bracing brackets offered FOC are also steel 0.090 not Ali as the prototypes are shown and require no welding to install .

 

[Adam]

Thanks for your insight jac

The brackets we already offered spread the load onto another much larger surface area and a plane perpendicular to the mounting surface of the primary turret mount helping to distribute the load down to the floor of the monocoque, larger than even you suggest necessary. This area of the floor also has internal bracing that creates the bulkheads inside the torque box area of the engine bay.

The "new bolt on brace" also create a cap over the top of the turret to help prevent runaway radius rods from cockpit intrusion which the modification done to Craig's chassis do not appear to have. This type of cap/safety option does not appear to be used on many other radius rod suspension style cars, real or replica, obviously an oversight on everyone's behalf , including mine especially in the modern world of more readily available and powerful engines ,stickier tyres and better brakes.

My Lola continuation spyder has a small 0.040 plate closing off the front of original design turret but it is not welded in place , only buck riveted. This is obviously acceptable as a period type modification , but without that the rod would be capable of direct cockpit intrusion with only a fiberglass bulkhead as protection .

The RCR bracing brackets offered FOC are also steel 0.090 not Ali as the prototypes are shown and require no welding to install .

Are those installed on my car up there? Can't wait to get that thing home.

 

[Jac Mac]

Thanks for your insight jac

The brackets we already offered spread the load onto another much larger surface area and a plane perpendicular to the mounting surface of the primary turret mount helping to distribute the load down to the floor of the monocoque, larger than even you suggest necessary. This area of the floor also has internal bracing that creates the bulkheads inside the torque box area of the engine bay.

Are these the brackets that go over the turret top that you have posted pics of on this thread already? Or have you devised another bracket/stay to support the lower end of the turret where the failure obviously initiates from....if so a pic might put my mind & others at rest.

 

[Fran Hall RCR]

The brackets do both Jac

Brace the turret and also create a captive cap

I am in vacation in the south of France with my family so any reply I make is out if sight and earshot of the missus

 

[Jac Mac]

The brackets do both Jac

Brace the turret and also create a captive cap

I am in vacation in the south of France with my family so any reply I make is out if sight and earshot of the missus

That's all?, just a couple of these? Good luck with that!
Honestly Fran, words don't fail me, just don't feel comfortable posting them.

 

[Fran Hall RCR]

No Jac not just a " couple of these"
There are four pieces to the brace/brackets and also additional fasteners per turret

I don't have any qualms whatsoever about these parts, their design or their strength.
Luck has nothing to do with it

I know of many other manufacturers that ignore failures and just scream foul or just hide behind their brand and make little to no effort to improve the safety or longevity of their product... That's not the case here.

You are entitled to your opinion and I am glad you have posted your concerns.

 

[Glenn B.]

I have finally returned to the forum and realized that I never closed the loop on this item for the folks who asked to see our final product.

We completed the repair and redesign of the rear control arm brackets. I'll be the first to admit that our solution is overengineered and overkill (and I'm sure Fran would agree on this point), but the goal was to both repair the car and my piece of mind. Here's what we did:

1. Welded a second aluminum plate on the top of the rear tub, doubling the thickness to provide more support at the fulcrum point and increase the overall strength of the section.

2. Fabricated the control arm mounts out of steel and fastened them both through the upper tub panel, and at the base, sandwiching the lower panel of the tub with steel plate. The pylons were made to be removable pieces that can be unbolted and slid out through the top of the chassis.

3. Changed the angle of the mounts to directly align with the control arms to eliminate all possiblility of bind or angled stress at the rod end.

4. Made both the upper and lower mounting points captive sockets to retain the rod end in the event of a failure. All AN hardware was used.

I'll repeat...this is an "overkill" solution... but it suits me just fine.

 

[Scott]

Thanks for posting the update. Your upgrade looks very well executed and thought out. Did moving the mounting points of the trailing arms affect handling at all? Thanks again, S

 

[Glenn B.]

There was no movement of the location of the mounting points or the length of the rear arms. All that we changed was the rotational angle of the pylon. Bottom line...no discernable change in handling.

 

[Scott]

Thank you sir. Looks like they are a little more inboard from the pics. I will be blowing the car apart sometime later this year to make some changes and was curious. S

 

[Jim DellaNeve]

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.

The welds look like they didn’t penetrate the tube. The metal under the wields was still intact. If the welds had melted the internal ply, then you’d get a crack through the entire material.