993GT

The 986>996>997 number updates to that 991 number now , maybe a catalogging issue?

powdrhound

It's possible. I think we looked at 991GT3/4 hubs and those were different if I recall correctly. Either way, the 991 hubs are still die cast pieces so nothing new there from a strength standpoint and there is no way to increase the area of the failure point due to the constraints of the bearing race and OD of the drive shaft splines. A forged material is really the only way to go. The 300M hubs will also be cryoed and heart treated. I wish there was a cheap solution. We looked at using the Grand AM Cup hubs but upon examination did not find them of any benefit from a strength standpoint.

rbahr

John,

Could you post some pictures of the failed hub?

Thanks

Ray

powdrhound

Failed OEM 996 hub (made by Brembo)

[url=https://flic.kr/p/oBB2Px]

[url=https://flic.kr/p/oBB39v]



Failed OEM 997 hub

[url=https://flic.kr/p/yuMdAv]

[url=https://flic.kr/p/za9GRV]

rbahr

Thanks,

I wonder what the root cause was... It would be interesting to have a ME look at these parts.

Have you looked at the RSR / cup car hubs?

Ray

powdrhound

Yes, we sent the hubs off to metallurgy to get an opinion. The verdict is the fact the material is a simple die cast steel that the hubs are made of. Die cast steel does not have a uniform grain structure and it's also fairly soft. The stress riser in the hub occurs at the sharpest radius which is exactly where the breaks are occurring. With the 300M hubs they were able to slightly increase the radius thereby further strengthening this weak spot. Obviously economics are at play with the OEM hubs as Porsche makes these for street cars where 99.9% will not have issues. The OEM hubs are very cheap at under $200 each and they are more than sufficient for their intended use. Heave track use is unfortunately not their intended use.

Yes, we looked at Cup hubs, specifically the Grand Am hubs which are not center lock but set up for a 5 lug set up. Surprisingly these hubs are also relatively inexpensive at several hundred per hub but they are still a simple die cast hub. I believe the reason you do not typically see failures of the Cup parts is most likely the fact that parts are swapped out on a much more frequent maintenance schedule that on street cars, many parts being changed out on an annual basis or an hour limited schedule.

rbahr

Thanks,

Gotta ask, With the money and time you have invested in this beast and the performance levels you are looking at, what about just timing out some of these parts? Carriers & wheel bearing say 20 hours / 1000 miles?

Ray

powdrhound

For the most part I do that already Ray. I also stay away from any of the aftermarket stuff instead sticking with genuine Porsche Motorsport parts like the RSR control arms, toe arms, etc.. The hubs just seem to be a particular weakness especially when run on a platform with a stiff suspension (1500 lb springs), sticky tires, and a high hp/tq engine. I believe I've just pushed that particular part past the design limit as it is always the left rear that fails, which just happens to be the most highly loaded corner on my car at my track (predominantly right turns).

rbahr

This is interesting to me because this is the point that I was with my last track car - A STi. Hubs & bearing were timed out every year - as was a number of other things. I STILL broke a lot, to the point where I just got a GT3.

My car has centerlocks (it came with them). The are just the standard part drilled out to receive the drive pins

The other interesting ting is that I don't see many places suspension wise, where the Porsche design envelope is exceeded...

The hubs you are getting built are quite nice.

Ray

powdrhound

Interestingly (knock on wood), I've never had any issues with axles or wheel bearings. The Porsche suspension seems to be very stout. I have seen a 6GT3 loose a rear LCA after the outer monoball failed. The result is not pretty as you can imagine. When I saw that I swapped out the standard LCA to the forged Motorsport RSR versions which have a much bigger fully rebuildable monoball on the outboard side.. This is a must have on a heavily tracked GT2/3 in my opinion. A few month ago I did manage to granade the left gearbox output shaft. It's thick steel and it snapped like a twig..

[url=https://flic.kr/p/G2apij]

[url=https://flic.kr/p/GkrjEc]

[url=https://flic.kr/p/FtJ8e4]

[url=https://flic.kr/p/Giabor]

rbahr

Wow, that is some carnage...

I totally agree with you on the aftermarket, not always worth the money. I did just get a set of 4 of the 'tarret' cup arms, not cheap, but worth it. I considered the MS stuff, but went with this because it was a bit easier, and these are very well made - it is a 14mm pin instead of 12... I hope the FAE work was done, and I suspect that it was.

I am 'lucky' in that I am still learning the car - really only 2 seasons at this point, so I am not as fast as many (yet)...

Ray

powdrhound

The problem with the aftermarket is that while it looks good it does not get put through the ringer like the battlefield tested Motorsport stuff. There is very little FAE for the aftermarket stuff as I have found repeatedly when it was put through the paces. While it looked good it the mono ***** were inferior (usually cheap FK or Aurora parts) and wore out quickly after a single season or simply flat out failed. You generally find the aftermarket stuff on cars doing DEs (where it's usually more than adequate) but won't find it on Cup cars in legit racing. Personally I've learned my lessons and just won't risk it anymore.

I do like Tarett as they make a lot of great products. Ira's service is top notch. They make very nice parts and I use their front extended drop links along with the rear DLs. The extended drop links are excellent. I do however wish that the quality of the mono ***** they use was better as they develop play with use. A few years ago I ran their monoball retrofit kit that I had installed in the stock LCAs. It worked well but again developed noticeable play after a single season (30 track days) which was frustrating. I've since swapped to the RSR arms and have several seasons on them. When I them checked last time, the German mono ***** were as tight as the day I put them on. Zero play, none... That was a wakeup call for me and a realization why going with the Motorsport parts was well worth the extra cost. Yes, they are more expensive but as the saying goes, you get what you pay for.

hf1

^this
Stress (and risk of failure) grows almost exponentially when stiffness, grip, and hp/tq are pushed beyond their intended ranges. When all three are pushed simultaneously the time of failure becomes anyone's bet. In that case, the most diligent approach would be to replace stressed components much sooner than even the most conservative expectations.

Smart to stick with Nittos until you come up with a stronger design/solution.

powdrhound

Agree. I also run a 63" Cup wing which provides a lot of downforce which is probably another contributing element.

AudiOn19s

Watching this closely. John, I just replaced both my rear hubs within the last 1500 miles when I refreshed everything else at the rear of the car but I'd be interested to know the cost of these as possible replacements down the road.

I was going through wheel bearings at an alarming rate about a year ago and I think hub wear was actually a contributing factor. After replacing the hubs, axles and bearings all at once my bearing issues have gone away.