strut tower failure
10-28-2019, 11:53 PM
#1142
So guys... what did, if anything we come up with? I figure for guys that are wanting to track and hold onto their GT4's are still thinking about a possible solution....
Went to the track last week and let me tell you those curbs really play mind tricks on you....
Went to the track last week and let me tell you those curbs really play mind tricks on you....
10-30-2019, 10:48 AM
#1143
Further, the strengthening ideas would need testing, and that is a whole other animal. I mean none of us can take a spare GT4 and go abuse it for a while to see if it holds up. This is why it really should be something that Porsche takes care of, because it requires R&D.
All that being said, I did have another idea couple of weeks ago, and rather than strengthening the towers, I though about limiting the travel. I know that is not a new idea, but I am not taking about a bump stop anywhere in the strut or the tower, but somewhere else. If it would work, it would pretty much be impossible for the towers to tear, as it would bottom out before. It would actually not be all that hard to manufacture, and installation would be just a couple of hours. But again, I need parts to play with. A front sub frame mainly, but a spare car would be better obviously. It could be a totaled car, if it had at least one front side intact. Maybe a race shop or some other shop be willing to work with me in conjunction. I can machine the parts, if they can help with the testing, installation and some designing (to fine tune) it.
10-30-2019, 02:09 PM
#1144
Drifting
By limiting the travel are you not simply increasing the power of the hit because the same force will be spread over a shorter time?
To me, one possible path would be to decrease the power of the hit by lengthening the duration that the force is applied - slow down the compression without passing the force directly through the shock due to non-compliance (as would happen if you shorten the travel, at least in my mind).
To me, one possible path would be to decrease the power of the hit by lengthening the duration that the force is applied - slow down the compression without passing the force directly through the shock due to non-compliance (as would happen if you shorten the travel, at least in my mind).
10-30-2019, 03:01 PM
#1146
I have several ideas that would have a good chance of preventing this, but the struggle I have, is that even though I have a machine shop, the reverse engineering is difficult without the solid models of the existing tower. I was hoping to get a damaged tower from a fellow member, but it never happened.
Further, the strengthening ideas would need testing, and that is a whole other animal. I mean none of us can take a spare GT4 and go abuse it for a while to see if it holds up. This is why it really should be something that Porsche takes care of, because it requires R&D.
All that being said, I did have another idea couple of weeks ago, and rather than strengthening the towers, I though about limiting the travel. I know that is not a new idea, but I am not taking about a bump stop anywhere in the strut or the tower, but somewhere else. If it would work, it would pretty much be impossible for the towers to tear, as it would bottom out before. It would actually not be all that hard to manufacture, and installation would be just a couple of hours. But again, I need parts to play with. A front sub frame mainly, but a spare car would be better obviously. It could be a totaled car, if it had at least one front side intact. Maybe a race shop or some other shop be willing to work with me in conjunction. I can machine the parts, if they can help with the testing, installation and some designing (to fine tune) it.
Further, the strengthening ideas would need testing, and that is a whole other animal. I mean none of us can take a spare GT4 and go abuse it for a while to see if it holds up. This is why it really should be something that Porsche takes care of, because it requires R&D.
All that being said, I did have another idea couple of weeks ago, and rather than strengthening the towers, I though about limiting the travel. I know that is not a new idea, but I am not taking about a bump stop anywhere in the strut or the tower, but somewhere else. If it would work, it would pretty much be impossible for the towers to tear, as it would bottom out before. It would actually not be all that hard to manufacture, and installation would be just a couple of hours. But again, I need parts to play with. A front sub frame mainly, but a spare car would be better obviously. It could be a totaled car, if it had at least one front side intact. Maybe a race shop or some other shop be willing to work with me in conjunction. I can machine the parts, if they can help with the testing, installation and some designing (to fine tune) it.
Not sure if the aluminum arms are strong enough to withstand the pressure.
10-30-2019, 11:25 PM
#1147
I am not sure either, but wouldn't you rather replace an aluminum arm, rather than a shock tower, in the event of bottoming out the suspension severely?
10-31-2019, 03:58 PM
#1148
Rennlist Member
^ How about a tether of some sort? Similar to the ones off-roader use to hold the suspension when its decompressed (full droop) over large jumps.
For the GT4 it can serve during compression of the front suspension. Maybe it can be mounted to the body/subframe and bottom shock bolt.
For the GT4 it can serve during compression of the front suspension. Maybe it can be mounted to the body/subframe and bottom shock bolt.
Last edited by 911F1; 10-31-2019 at 07:13 PM.
11-02-2019, 04:58 AM
#1149
Sorry if this has been answered recently above - ive read most of this thread - anyone yet viewed the newly delivered Cara in Europe to see if they have had any mods to suspension or turrets? Snowy
11-04-2019, 02:46 PM
#1150
Burning Brakes
Has any competent authority, i.e., Porsche, concluded with empirical evidence that the tower failures are caused by suspension bottoming, whether due to frequency or a single catastrophic event? Versus tower fatigue perhaps caused by a number of other variables. And of course PASM (especially on GT suspensions) can introduce great forces similar to bottoming by disallowing suspension travel based on what conditions the OEM controller is programmed to react to. Rapid unloading of a suspension is also violent, such as encountered during off track excursions through bumpy ground. Deep potholes are violent because of the strut instantly unloads shooting the strut to its full length in a microsecond. That bang is more suspension unloading (to the max strut length limit which is abrupt) than the tire hitting the subsequent edge of the hole. Anyway, aren't the towers the same on all 981s? If bottoming is the culprit, regular 981s would bottom much quicker as suspension rate is much softer and isn't designed to counter the forces of tracking. What's the failure rate on tracked pedestrian 981s comparatively?
Has anyone asked DSC their thoughts on the force generated by OEM controller during heavy braking versus their controller which better controls dive and gives the suspension far more compliance (equaling less fatigue)? Dive equals a great increase in suspension force certainly, but is there actual proof the suspension bottoms in a violent enough way to cause these failures? Or is this just assumed??
Has anyone asked DSC their thoughts on the force generated by OEM controller during heavy braking versus their controller which better controls dive and gives the suspension far more compliance (equaling less fatigue)? Dive equals a great increase in suspension force certainly, but is there actual proof the suspension bottoms in a violent enough way to cause these failures? Or is this just assumed??
11-04-2019, 04:46 PM
#1151
Three Wheelin'
How about a stiffer longer spring from Swift in the front. Ira at Tarret certainly has plenty of experience with this. His GT4 kit has springs that go up like 50 lbs in the rear and about 100 lbs in the front to better balance the car for the track. All other things being equal that is an extra 50 pounds in the front, so maybe just getting springs up front that are 50 pounds more would help. Adding a half inch or an inch to their length would also increase travel if there was enough thread on the strut tower to lower the spring perch. Finally it seems most people set the front sway bar at full soft and the rear at full hard to compensate for factory understeer. Maybe other things could be done to the suspension set up to be able to run the front bar on a stiffer setting. This would let the other strut help carry the load from the one being abused.
It has been so long, 77 pages ago, I am not sure anymore to what detail the above has been already discussed.
It has been so long, 77 pages ago, I am not sure anymore to what detail the above has been already discussed.
11-05-2019, 02:35 PM
#1152
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Has any competent authority, i.e., Porsche, concluded with empirical evidence that the tower failures are caused by suspension bottoming, whether due to frequency or a single catastrophic event? Versus tower fatigue perhaps caused by a number of other variables. And of course PASM (especially on GT suspensions) can introduce great forces similar to bottoming by disallowing suspension travel based on what conditions the OEM controller is programmed to react to. Rapid unloading of a suspension is also violent, such as encountered during off track excursions through bumpy ground. Deep potholes are violent because of the strut instantly unloads shooting the strut to its full length in a microsecond. That bang is more suspension unloading (to the max strut length limit which is abrupt) than the tire hitting the subsequent edge of the hole. Anyway, aren't the towers the same on all 981s? If bottoming is the culprit, regular 981s would bottom much quicker as suspension rate is much softer and isn't designed to counter the forces of tracking. What's the failure rate on tracked pedestrian 981s comparatively?
Has anyone asked DSC their thoughts on the force generated by OEM controller during heavy braking versus their controller which better controls dive and gives the suspension far more compliance (equaling less fatigue)? Dive equals a great increase in suspension force certainly, but is there actual proof the suspension bottoms in a violent enough way to cause these failures? Or is this just assumed??
Has anyone asked DSC their thoughts on the force generated by OEM controller during heavy braking versus their controller which better controls dive and gives the suspension far more compliance (equaling less fatigue)? Dive equals a great increase in suspension force certainly, but is there actual proof the suspension bottoms in a violent enough way to cause these failures? Or is this just assumed??
I know this has happened on GT3's, too, but my guess is that it's happening with a lower overall rate (as there are probably a lot more GT3's on track) thanks to the GT3 having a tad more travel. The extra travel means the obvious thing in that it takes a bigger hit to get it to bottom, but I think more importantly than that is it gives the damper more time to react and temper those forces before said impact happens.
It's telling that PCA did the bulletin to allow the "stock" class cars to run the motorsport plates on top. Well, the telling part is what they don't say. They don't require them and they also don't say what they'll do for you. I don't think there's 100% confirmation of this, but I feel relatively certain that those exist simply as a safety device to help keep the strut from going very far if the top does blow out, thus helping the driver maintain control if it happens at speed. It's a bonus that it keeps your hood from being damaged, and I doubt seriously those plates will do much, if anything, to help stiffen the strut tower.
I also doubt anyone finds a way to stiffen the strut tower that fixes this. One problem is that the right fix is to add something to the entire inside of the cup. But doing that is going to take away precious suspension travel, which is going to further exacerbate the problem. I understand the thought process behind "stiffer spring", but *that* is also going to introduce other ill effects. I think the main culprit here is inadequate damping from the shock, and if I'm correct on that, then a stiffer spring MAY help up to a point, and past that point will definitely make the problem WORSE. Especially if the above is correct in that rebound of the shock could also be shocking the strut tower...you won't have enough rebound to control that stiffer spring, either.
Additional bump stops? Maybe, but again, that's going to limit your suspension travel that much more.
Personally, if I had a GT4 that I loved (and the only reason I don't is that I already had one built before Porsche did it, a Farnbacher GTR), I'd consider better shocks. At the very least, the DSC module actually sounds promising, too. The poster early on who tried his car on the same road both with and without it seemed telling. And I'd put about $30k away just in case. *sigh*
--Donnie
11-05-2019, 03:49 PM
#1153
Burning Brakes
The reason people seem to be assuming bottoming out during compression is the problem is that evidence seems to suggest this problem is more likely on the car with the least amount of upward travel available, the GT4. The OP in this thread had this happen on a very low mileage and stock GT4 that was autocrossed but not tracked and saw no heavy hits or curbing other than the single pothole (which was only bad enough to damage a stock 20" rim so slightly only a machine could detect it...tire didn't even deflate). The OP even went so far as to send out his broken tower to a very high end testing facility who determined that while there was a previously existing crack that was then blown out by the pothole, they found no casting imperfections and did discern the alloy used was a "very strong" one.
I know this has happened on GT3's, too, but my guess is that it's happening with a lower overall rate (as there are probably a lot more GT3's on track) thanks to the GT3 having a tad more travel. The extra travel means the obvious thing in that it takes a bigger hit to get it to bottom, but I think more importantly than that is it gives the damper more time to react and temper those forces before said impact happens.
It's telling that PCA did the bulletin to allow the "stock" class cars to run the motorsport plates on top. Well, the telling part is what they don't say. They don't require them and they also don't say what they'll do for you. I don't think there's 100% confirmation of this, but I feel relatively certain that those exist simply as a safety device to help keep the strut from going very far if the top does blow out, thus helping the driver maintain control if it happens at speed. It's a bonus that it keeps your hood from being damaged, and I doubt seriously those plates will do much, if anything, to help stiffen the strut tower.
I also doubt anyone finds a way to stiffen the strut tower that fixes this. One problem is that the right fix is to add something to the entire inside of the cup. But doing that is going to take away precious suspension travel, which is going to further exacerbate the problem. I understand the thought process behind "stiffer spring", but *that* is also going to introduce other ill effects. I think the main culprit here is inadequate damping from the shock, and if I'm correct on that, then a stiffer spring MAY help up to a point, and past that point will definitely make the problem WORSE. Especially if the above is correct in that rebound of the shock could also be shocking the strut tower...you won't have enough rebound to control that stiffer spring, either.
Additional bump stops? Maybe, but again, that's going to limit your suspension travel that much more.
Personally, if I had a GT4 that I loved (and the only reason I don't is that I already had one built before Porsche did it, a Farnbacher GTR), I'd consider better shocks. At the very least, the DSC module actually sounds promising, too. The poster early on who tried his car on the same road both with and without it seemed telling. And I'd put about $30k away just in case. *sigh*
--Donnie
I know this has happened on GT3's, too, but my guess is that it's happening with a lower overall rate (as there are probably a lot more GT3's on track) thanks to the GT3 having a tad more travel. The extra travel means the obvious thing in that it takes a bigger hit to get it to bottom, but I think more importantly than that is it gives the damper more time to react and temper those forces before said impact happens.
It's telling that PCA did the bulletin to allow the "stock" class cars to run the motorsport plates on top. Well, the telling part is what they don't say. They don't require them and they also don't say what they'll do for you. I don't think there's 100% confirmation of this, but I feel relatively certain that those exist simply as a safety device to help keep the strut from going very far if the top does blow out, thus helping the driver maintain control if it happens at speed. It's a bonus that it keeps your hood from being damaged, and I doubt seriously those plates will do much, if anything, to help stiffen the strut tower.
I also doubt anyone finds a way to stiffen the strut tower that fixes this. One problem is that the right fix is to add something to the entire inside of the cup. But doing that is going to take away precious suspension travel, which is going to further exacerbate the problem. I understand the thought process behind "stiffer spring", but *that* is also going to introduce other ill effects. I think the main culprit here is inadequate damping from the shock, and if I'm correct on that, then a stiffer spring MAY help up to a point, and past that point will definitely make the problem WORSE. Especially if the above is correct in that rebound of the shock could also be shocking the strut tower...you won't have enough rebound to control that stiffer spring, either.
Additional bump stops? Maybe, but again, that's going to limit your suspension travel that much more.
Personally, if I had a GT4 that I loved (and the only reason I don't is that I already had one built before Porsche did it, a Farnbacher GTR), I'd consider better shocks. At the very least, the DSC module actually sounds promising, too. The poster early on who tried his car on the same road both with and without it seemed telling. And I'd put about $30k away just in case. *sigh*
--Donnie
11-05-2019, 05:16 PM
#1154
FWIW... I got rid of the helper springs, which allowed for longer linear springs (higher rate as well) which allows for more "work" to be done by the springs in reducing the possibility of bottoming out.
I have no data to suggest that this is effective, but my knowledge of suspensions, along with some bench talking with people waaay more knowledgeable that me on the topic, gives me some sense (imagined or not) of security.
YRMV...
I have no data to suggest that this is effective, but my knowledge of suspensions, along with some bench talking with people waaay more knowledgeable that me on the topic, gives me some sense (imagined or not) of security.
YRMV...