GT4 strut top failure

[bigmowley]

Picture from social media. Apparently on track and kerb hopping!!!!!!! Not that we would ever do that obviously .
More info please

[Turn7]

is that for real ?

[lanan]

Flippin eck.
God only knows how the race car will cope, if that's a road car.

[Evolved]

The race cars will be seam welded and strengthened with roll cages and box sections I would have thought so that won't be a weak area.


There had to be a fault there though for it to give like that.

[Slippydiff]

Evolved said:

The race cars will be seam welded and strengthened with roll cages and box sections I would have thought so that won't be a weak area.

I doubt it, the section of the bodyshell that has failed is formed from what looks to be an aluminium casting or forging that has possibly failed due to a forging/casting or adhesion/bonding fault.

http://european-aluminium.eu/media/1543/1_aam_body...

(page 79)

The race car rollcage has a tubular section which protrudes through the front bulkhead to the strut top/inner flitch to provide some additional (maybe much needed...) strength and support. But no obvious seam welding or additional box sections.



Edit to add, the strut top mount on the GT4 clubsport race car looks to be a bespoke (991 Cup car ? ) mount too.

Edited by Slippydiff on Thursday 11th August 00:01

[Steve Rance]

The biggest load points on the chassis are the front suspension turrets. The designers aim will be to prevent the loads from translating themselves through the chassis causing twisting or bending. This would prevent the cars suspension from functioning correctly and the chassis would effectively become a giant torsion bar. The cage extensions to the turrets in the race version of the Cayman are located to counter the additional torsional loads created by slicks and the much stiffer suspension fitted to the car.

A flexible chassis is one thing but a turret failure is something far more serious. I have never seen a turret fail like this before. I would see this as more worrying than the engine failures associated with the 991GT3 as the implications are far greater. Very odd given the loads that the turrets are designed to endure and the structural significance of that area of the chassis. The Caynan and especially the GT4 has a particularIy stiff chassis which makes this event even more unusual. I suspect there is a hidden story behind this event. Hopefully Porsche will give the market some comfort by explaining it.

[ras62]

That race car picture shows a black strengthening plate mounted over the top of the original strut? I wonder if that could be a mod fitted to the road car. A serious issue for sure and a weak spot recognised by the factory judging by the change to the race cars.

[ooid]

Is it really about chassis or suspension? I remember reading somewhere, a tiny discussion about GT4 and 911's rear suspension difference. (GT4's completely new)

[Steve Rance]

A strengthening plate would be welded not bolted if it were a real issue. The problem is most certainly chassis. The chassis should hold together even with the stiffest of spring/shock combinations. It will probably flex a fair bit but it should hold together. The GT4 has bushes and is not rose jointed which will absorb a fair bit of load and prevent it from passing up to the turret.

Very odd failure.

[Steve Rance]

Ha! True.

[ooid]

What is the actual material on that area?

Specs say "Intelligent lightweight construction with aluminum-steel composite"

Would be nice to see a cross-section of the chassis only, checking the surface and thickness. (Have not seen before, apologies if its too ignorant)

---

Responding my own question , I guess the affected area is the green ? - "mikrolegierte stähle"- (If GT4 also shares the same material of 981 body as this illustration below?)

Edited by ooid on Thursday 11th August 21:59

[Slippydiff]

The area that's failed is blue (aluminium). It looks to be a cast or forged part as the underside of the turret has strengthening webs and is a thicker section than the surrounding metalwork.

[Buffalo Girls]

It would be interesting to see what state the wheel and tyre are in on this car

[EGTE]

This happened to Jari-Matti Latvala in Rally Argentina.

http://www.wrc.com/en/wrc/news/april-2016/latvala-...

But he was going very fast (for a rally car) and hit a massive rock, which gives you an idea of the forces involved.

If this happened on track, there would have to be something seriously wrong with the design.

[FrankCayman]

Excuse my ignorance, but how would they go about repairing damage like that?

[griffter]

It looks like a catastrophic fatigue failure to me. I'd be amazed if the strut mount was cast, but I agree the ribs underneath would suggest that.
Failure mode is similar to bending and straightening a spoon. Do it enough times and it'll break as microscopic cracks propagate.
Presumably on this car the kerb fatigued the part beyond its elastic limit until it failed. All speculation of course, but perhaps indicative of the risks of cutting edge materials and manufacture (over good old pressed steel).

[GT4P]

What is the full story behind failure? Was it an accident? It just seems a bit random as the gt4 chassis is mainly the same as any 981 which have been built for 4 years and of which a few have seen track action over years especially across the pond yet this is the first case to hit the net!

[EricE]

FrankCayman said:

Excuse my ignorance, but how would they go about repairing damage like that?

I am curious too. They could cut it out and weld a good dome in (not sure how comfortable I would be with that?) or reshell the whole car. Yikes.

[Trev450]

EricE said:

FrankCayman said:

Excuse my ignorance, but how would they go about repairing damage like that?

I am curious too. They could cut it out and weld a good dome in (not sure how comfortable I would be with that?) or reshell the whole car. Yikes.

I would imagine they would replace the complete inner wing which of course incorporates the strut tower.

[cd1957]

Hi the strut support is shown as a separate part for £222.00.

I would want Porsche to explain why this cant take the load, as some of the potholes are huge.

Chris