This^^. There is just no upside to using unproven parts. The risk is just too great as you can do a lot of carnage to the car (and yourself) if a key suspension component fails. The risk is always there but largely mitigated if you go with race proven parts that the factory uses on their top of the line race cars like the RSR. The extra cost in using the real deal is worth it if you are tracking these cars with aggression...

 

That's why you need to keep as much of the stock geometry as possible or be prepared to do trouble shooting. Johns issues are certainly related to the geometry changes from the cup and rsr parts he's added. No way a stock geometry TT eats hubs like that. When you change uprights, pickup points stress angles etc, younget to re-engineering and that becomes risky. Most everything on the suspension is very robust but only in so far as it was designed to operate. I have run almost track only for 10 years and not lost a hub. Hubs are not wear items on our cars. Just replaced the original axles a few weeks ago. It just goes to show you how small changes can make a big difference. No one here has reached the limits of the stock geometry yet. Even lowering it too far causes problems. You have to have a toe kit with bump steer adjustment or you will burn through slicks almost daily and they will blow out. DOT tires last ok but with high DF, and true slicks, your tires will blow out.

I had a wheel failure in turn 1 at Road Atlanta, lesson learned. I also had 4 wheel studs break in turn 12, 1 wheel bolt held the wheel on. Keeping with wheel bolts is better albeit slower when changing the wheels.

 

Here is the description of the ERP units from Tarretts website. Pro-Series Control Arm Kit




$1,800.00
Select Application 996/986/997/987/991/981 Front & 996/997 Rear (# ERP-LCA-F) Select Here (-$1,800.00) 986/987 Rear (# ERP-LCA-R) (+$50.00) 991/981 Front (#ERP-LCA-F-12) 981 Rear (#ERP-LCA-R-12) (+$50.00) Select Litronic Bracket Option Select Here 991/981 Front (x2 #LTBRKT2) (+$70.00) 997/987 Front (x1 #LTBRKT2) (+$35.00) 981 Rear (x2 #LTBRKT981PRO) (+$100.00) 987 Rear (#LTBRKT981PRO) (+$50.00)



Introducing the latest innovation in competition suspension products for your Porsche 986/997/986/987/981 & 991. Designed and manufactured by the ERP Suspension Engineering, this unique lower control arm design is far superior in reliability, quality, and performance to anything else available on the market today.

These bad boys are more than just a machined replica of the factory arms. The ERP Pro-Series lower control arms are fabricated from aerospace quality 4130 chromoly steel, tig welded together, and then heat treated and finished with protective coating of electro-less nickel. Camber, caster and wheel base can all be adjusted quickly and precisely with a simple turnbuckle link design. No shims to add or remove. In addition, this kit includes precision adjustable diagonal links for fine tuning caster and adjusting wheel base. All pivot points, at the chassis connection consists of oversized precision grade Teflon lined rod ends. The ball joint also consists of oversized precision grade Teflon lined monoball bushings. The diagonal link to the chassis connection point uses the 997 RSR design which allows it to be raised or lowered to reduce squat and dive during acceleration. For safety, the problematic 12mm ball joint design, used on both OEM and aftermarket arms, has been completely redesigned for a full proof, significantly stronger, and more reliable design that you can count on. To top off this no compromise design the center geometry can also be adjusted to correct for lower ride heights. All kits come complete for one axle with all the parts and hardware necessary for a bolt in direct replacement for the OEM arms.

• No-compromise design
• Precision camber adjustability
• Precision caster adjustability
• Precision wheel base adjustability
• No shims required
• Chromoly construction
• Electroless nickel finish
• Roll center adjustability
• Squat and dive reduction
• Superior quality, performance, and strength

 

you might know this answer but which would be considered a better material? the 4130 chromoly or the 6061 aluminum for this application? i see the spl gives some specific material that they use but gmg just lists the 4130 chromoly

 

The Cup/RSR suspension parts have absolutely nothing to do with geometry on my car. The parts themselves as dimensionally the same as street parts and as such do not change the geometry of the car which is the same as what you have on any 6GT2/3/Cup. Pick up points are NOT changed. The alignment has more aggressive camber but that has nothing to do with snapping hubs, transmission output shafts, lsds, etc. I had a metallurgical analysis done on the failed parts and listed the conclusions as to the cause of the failures in a different thread so I won't rehash it here again but rest assured it's not geometry.

No, the stock parts won't fail under normal use but when you track these cars hard parts will eventually fatigue and fail. As you know Cup cars or any race cars are put on a much more agressive maintenance schedule where components are continuously timed out and regularly swapped out to preclude or minimize failures. That's nothing new. Wheels and studs will fatigue also and I time those out as a precaution to preclude failures like many guys including yourself have experienced even though I believe we have solved the mystery of why so many guys are snapping studs.

 

You guys are funny. These may be very well made parts, who knows? Someone buy them and test them versus the forum banter back and forth over who knows what. As far as saying someone had hubs fail, that has to be from some other issue.. Hubs just don't fail, ever! And Heavy that's concerning having hearing you had failed wheel studs, but I would attribute that to maybe a bad batch or bad metal that fatigued over saying wheel bolts are better. I run studs and have for years w/out issues. Additionally, I would rather have the wheel clamped via stud setup than just a bolt through the face.

Also one thing to remember, at one time, all parts were unproven.

 

w/out pulling up another issue, what was the cause? Hubs just don't fail on cars.

 

The one problem with those parts is the use of the FK heim joints in my experience just do not hold up long term. Tarett, whose stuff I like, uses FK and/or Aurora heim joints and they just don't last. Every part that I used has developed play in the monoball with hard use after a season or two. This goes for their LCA monoball cartridges and drop links. The German monoballs used on the Motorsport parts on the other hand have stayed rock solid without a hint of any play even after several years of use. Made a believer out of me.

 

I never had issues with hubs until I started running the car continuously very hard. That's when the hubs started failing. It was actually always the left rear which is the most highly loaded corner at the tracks I run. After breaking two hubs we sent the failed parts to a metallurgist. The verdict was the simple fact that that when you combine high lateral loads (cornering) with very high twisting loads (engine torque) it imparts a level of metal fatigue that eventually leads to failure. Take away one or the other and it would not be an issue.

The contributing factor also is the fact since the suspension is full monoball there is no rubber that would provide a cushioning effect thus limiting peak shock loads. Everything is transferred directly to the hubs. Additionally, since I'm running a stiff suspension with 1500lbs springs, there is much less dampening of peak shock loads than what you would get with a soft/squishy suspension. Makes sense. A tight LSD set up aggravates the situation with sticky Rcompound/slicks and 670+ft.lbs of torque at the wheels providing the twisting force. When you combine this with 1.4-1.5G cornering loads, bouncing of curbing, etc., you are imparting tremendous peak loads that are being absorbed by the hubs and other suspension components. When you do this continuously for 40, 50, 60+ hrs, you will eventually reach a point of failure. The opinion was that if the twisting loads were reduced than the hub would have a much greater life span. I can't recall what they said the hubs came in on the Rockwell hardness scale but they are relatively soft as they are simple castings. The 300M hubs I had manufactured have roughly a 100% greater failure threshold than the stock hubs.

So why do Cup cars not suffer these failures even though they still the same stiff 1500lb sprung suspension? 996 RSRs actually run 1970/2140lb springs! For one thing they have very little engine torque thus taking away the twisting load the hubs are subjected to. Additionally the cars are 600-700lbs lighter which reduces the lateral loads the hubs are subjected to. Finally, most race teams swap out these components along with wheel bearing on a regular basis. These cars are subjected to a pretty intense maintenance schedule. Finally, Porsche did redesign the Cup center lock hubs going with a beefier design than what was used previously. They did this for a reason as there was probably evidence of failure or cracking with the old parts.

I'll touch on wheel studs which many guys have had issues with as was mentioned earlier. The failure of studs indicates a failure due to repeated flexing of the stud with eventually leads to cracking and failure. Flexing indicates an insufficient clamping force of the wheel which allows a small amount of flex to be impart on the stud. Ever since we went from the 96ft.lbs tightening torque to the 118ft.lb spec on the 991 and later cars, these issues have seemed to completely go away and the wheel clamping force increased and precluded any flexing of the stud. I know that when I used to use 96 I would have to keep retightening the lug nuts after the first few runs. With 118, I don't have any issues. 96 is actually very low for a 14x1.5mm stud and is a carryover from when Porsche used the aluminum lug nuts on the old air cooled cars. We have not broken a single stud on any of our race cars and we run those in 8/12 and 24hr endurance races. Zero stud failures over the last 3 years since using 118. Regardless, I replace studs on my car every 2year or 100hrs of track use since they are cheap. We use German H&R studs on all of our cars.

 

John, there is no way twisting force is whats breaking your hubs that fast when plenty of cars have run as much or more hp and even stickier tires for years. Didnt you break one in only a couple of events? No possible way. The stock hubs are capable of accepting more torque than the tires can even put down many times over. The way they failed of course shows that it twisted loose, but common sense says otherwise.

Wheel studs are wear items. Race cars replace them yearly. I waited a couple months too long. My point was that when you change stuff and alter the original design, parts can break. Gators and curbs can also break them due to certain vibration frequencies. Take a look at the wheel failures F1 had this year due to vibrations. Porsche parts will almost always have the most testing and collected data vs 3rd party shops. But even Porsche parts break after a while, control arms have been known to break which is why on cup cars they are wear items. If you change the design to an unknown, you now become the engineer to fix whatever issue come up as Porsche would not have tested your variables. The more you change, the more you will likely have to correct.

 

Dez, I'm certainly no metallurgist but this is what they told me as posted above. The original failed hub was 15years old with 150+ track hours. The replacement hub lasted 2402 track miles and 45.8 track hours. I'm not discounting the fact that the replacement hub may have been flawed from the start. I come from an aviation background and know it only takes as small imperfection in the casting to cause a stress riser leading to failure. Remember the Sioux City United DC10 crash years ago? A 600,000lb aircraft was brought down by a microscopic flaw in the titanium casting of the #2 engine fan that propagated into a crack leading to a rupture of the fan. The flaw was the size of a pin head.

Regardless, anything can fail if you stress it enough including the hubs. How many guys do you know that have exploded a gearbox output shaft? I did this earlier this year. Again a twisting force caused this as there is no other force imparted on this piece, strictly a twisting force. You can clearly see that below. Most track set ups are running torque in the 500-550 ft.lb area while I'm about 20% higher at 670+. Maybe this is enough to push these parts over the edge when subjected to this over extended periods of time? Parts may operate for a 1000hrs at a 70% load limit but their life expectance may be reduced to 200hrs when operated at 90%. At 95%, maybe 50hrs. This is no secret. Yes, many guys are running 1000hp though these cars but they are not operated at that level continuously as we do on a racetrack.

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

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

 

John, my point is that the turbo is not a GT2 or GT3 so yes the geometry from a turbo is changing with upgraded parts. When I say geometry I mean the normal range of motion and dynamics (camber, caster and toe) for which the original suspension was designed. When you move to very low ride heights and then adjust to prevent bump steer and then move in roll centers etc a lot has changed. Both you and myself as well as others have gone far from that, and at certain stages there are consequences. Something as simple as low ride heights, like I said will stress a different area and cause premature tire failures. QUICK. I cant fathom losing 2 hubs in quick succession like that. A bad hub is certainly an option. Tom Kerr and Al Norton both ran well into the 600 wheel hp and torque ranges. You arent using 670 torque mid corner let alone on Kumhos and NT01's. Maybe apex to exit at which point the increasing momentum mitigates some of the impact to the stress points. Gears usually go well before hubs on our cars. Then axles. Honestly I would rather it that way. Hopefully it was a bad hub, but thats a scary situation either way.

 

Heavychevy,

While I respect your knowledge and contribution, I respectfully have to disagree with your view. You are not taking into account heat cycles induced by the brakes in addition to lengthy track sessions. A turbo or GT2 that can lap similar times as a cup or GT3 will almost always be harder on brakes.

 

I get it Dez. I wasn't even considering a stock TT suspension/alignment/geometry. The goal of the TT was a grand tourer and not a track car. My car really has nothing common with the TT anymore besides what it says on the title as the suspension along with everything else is essentially identical to a GT2/3/Cup so I was making the comparison to the GT/Cup cars and not the Turbo.

There is no question the way we operate these cars for hours on end will unquestionably stress components to their limit and with enough time and cycles, beyond their limit. If I can burn a set of tires down to cords in 200 miles of track time, obviously I'm putting some stress on the chassis and car as a whole than when I was getting 400miles out of the same set. My car has been unbelievably reliable but I do time out and replace components before they would be a problem. I log all time and miles that are put on the car and can reliably keep track of time and miles on all parts installed.

I swap axles every 50 hours for example. Later this month were are dropping the gearbox and doing a proactive overhaul as it's gone two seasons since the last refresh. Last year we swapped in a new 1-3 and this time I'm doing a new 4th. If any other parts look iffy, they'll be replaced. We may end up swapping in a new crown and pinion this time depending what it looks like upon close examination as we have been keeping an eye on it last time my gearbox was out. The R&P replacement interval on a 996Cup is 8000Km for example and I'm way past that on essentially the same gearbox with almost double the power going throughout it. I just had my billet Guard LSD freshly rebuilt a couple of months ago but will now be installing Guards flagship chromoly GT2 PRO LSD which finally came in after the order was placed this past summer. I believe keeping the car on a continual maintenance schedule proactively replacing parts is why I've had such utter reliability from the car. The 300M hubs that I have now are going to mitigate the one thing that has been an issue for me.

 

I am unsure here as well:
- on the one hand I have to agree with VAG and pwdrhound. John was running not too far off Cup car level with a car that weighs more, has more chassis flex (due to not having a full cage), etc. And he was making up for all the chassis/car deficiencies with power/torque. That this is bound to put more than a little extra stress on the hubs is obvious.
- on the other hand, I know several people running 996tt's in a similar fashion to John. And I know of several more (not to mention board members such as Kaizu or Pete). I have not heard of anyone else having problems to this extent with their hubs.

John, in the interest of science you will have to continue running stock hubs. If you go through at least one more breakage, we can all but eliminate a material flaw. Unless of course there was a bad batch...

I hope next summer I can add my experience with hubs to the discussion. My chassis setup will be very similar to John's and if things go as planned, I hope to have power levels around the same as his were with the OEM engine internals by mid-summer. And, time and circumstances allowing, I hope to be at our local track relatively often for practice and continual tweaking of the car: http://www.anneau-du-rhin.com/infos/club/
Lots of hoping. I also hope that John had a material flaw in his replacement hub.