Strut towers dancing?
12-27-2016, 09:19 AM
#1
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Strut towers dancing?
Hi all,
Has anyone actually instrumented and recorded what happens to the 944 strut towers when driven hard. I understand from searching that the braces actually do add rigidity to the chassis. Do the towers spread apart or move together? Also, what motion in the towers is controlled by the Turbo S gussets that were added.
Thanks,
Gord.
Has anyone actually instrumented and recorded what happens to the 944 strut towers when driven hard. I understand from searching that the braces actually do add rigidity to the chassis. Do the towers spread apart or move together? Also, what motion in the towers is controlled by the Turbo S gussets that were added.
Thanks,
Gord.
12-27-2016, 11:06 AM
#3
Race Car
Interesting Van!
----
STOLEN (I stole this):
"Originally Posted by Oddjob
Ive been equally skeptical of any single modification that is marketed as a “big” improvement. But here is my current thinking on Strut Tower Bars.
Stiffening up the chassis, to reduce chassis flex probably has different effects on handling characteristics than does changing spring rates and sway bar settings.
Chassis stiffening can be accomplished by several means and to several levels of severity. Installing a roll cage (various types from bolt-in to custom welded in) all the way up to seam welding the body panels will stiffen a car up. Although it can alter the handling characteristics of the car because there is less body flex to account/compensate for with other suspension settings and setups, I would not necessarily consider this tuning the suspension.
With the front shock towers, the concern is that the outside shock tower deflects outward under corner loading. So if that is the case, it will change the camber on the outside wheel to a more positive wheel angle. Depending on the initial camber setting, this could reduce grip. So in theory, if the strut tower movement is reduced/limited by adding a STB, it could keep the alignment settings from deflecting (outside of the change inherent to a McPherson strut), which could actually make the car turn-in better (…?).
Now how much does a non-supported shock tower deflect? Who knows? How much does that deflection adversely affect handling? Does a STB offer that much chassis stiffening to actually improve handling?
I don’t know. Just like I don’t know how much (quantitatively) a full cage stiffens a chassis or how much seam welding does. Some people say you can really feel the difference, others say you cannot.
Keep in mind that the frame design of these cars goes back to the 924 in the early-mid 70’s. I don’t think the tub of the car was ever really altered/reinforced since that initial design. Porsche never intended the street cars to be run with solid bushings, 500 lb/in springs, 18” 245/285 Hoosiers. In a DE/Race application, my guess is that there probably is quite of bit of body flex - e.g. Ive seen a rear quarter window shatter on a 944S2 during a race practice.
When the factory did race the cars, they installed a strut brace (in the Turbo Cups and S2 Club Sports). And take a look at Jason B’s 968TRS and see the weld-in cage that the factory installed. See the pick-up points that the factory reinforced. They ran roll bar tubing out through the firewall to the shock towers and also used a STB to reinforce them. My guess is that the factory felt there must be some movement there in racing applications.
I was forced off track at my last club race and my car hit a berm. The right front shock tower was pushed up and inward. I pulled the motor and front suspension out to have the frame straightened. Also, the heat shielding was removed from the engine bay, and the fender came off. If you take a good look at the way the front frame members and shock towers are made, how thin the sheet metal is (and where it flexed and bent on my car), that its all just spot welded together - its amazing these cars hold together as well as they do (it looks weak). So, I will be adding a STB when rebuilding the car.
Depending on your type/level of driving you may or may not notice anything with adding a STB. I would think that for street use on street tires, you will never corner hard enough to deflect the shock towers enough to feel a difference in handling. In auto-x, DE, and racing, its quite possible that a car with big, fat R-compound tires, upgraded suspension, etc may be able to corner hard enough to noticeably deflect the shock towers. If that’s the case, then the car/driver could potentially benefit from a STB. "
----
STOLEN (I stole this):
"Originally Posted by Oddjob
Ive been equally skeptical of any single modification that is marketed as a “big” improvement. But here is my current thinking on Strut Tower Bars.
Stiffening up the chassis, to reduce chassis flex probably has different effects on handling characteristics than does changing spring rates and sway bar settings.
Chassis stiffening can be accomplished by several means and to several levels of severity. Installing a roll cage (various types from bolt-in to custom welded in) all the way up to seam welding the body panels will stiffen a car up. Although it can alter the handling characteristics of the car because there is less body flex to account/compensate for with other suspension settings and setups, I would not necessarily consider this tuning the suspension.
With the front shock towers, the concern is that the outside shock tower deflects outward under corner loading. So if that is the case, it will change the camber on the outside wheel to a more positive wheel angle. Depending on the initial camber setting, this could reduce grip. So in theory, if the strut tower movement is reduced/limited by adding a STB, it could keep the alignment settings from deflecting (outside of the change inherent to a McPherson strut), which could actually make the car turn-in better (…?).
Now how much does a non-supported shock tower deflect? Who knows? How much does that deflection adversely affect handling? Does a STB offer that much chassis stiffening to actually improve handling?
I don’t know. Just like I don’t know how much (quantitatively) a full cage stiffens a chassis or how much seam welding does. Some people say you can really feel the difference, others say you cannot.
Keep in mind that the frame design of these cars goes back to the 924 in the early-mid 70’s. I don’t think the tub of the car was ever really altered/reinforced since that initial design. Porsche never intended the street cars to be run with solid bushings, 500 lb/in springs, 18” 245/285 Hoosiers. In a DE/Race application, my guess is that there probably is quite of bit of body flex - e.g. Ive seen a rear quarter window shatter on a 944S2 during a race practice.
When the factory did race the cars, they installed a strut brace (in the Turbo Cups and S2 Club Sports). And take a look at Jason B’s 968TRS and see the weld-in cage that the factory installed. See the pick-up points that the factory reinforced. They ran roll bar tubing out through the firewall to the shock towers and also used a STB to reinforce them. My guess is that the factory felt there must be some movement there in racing applications.
I was forced off track at my last club race and my car hit a berm. The right front shock tower was pushed up and inward. I pulled the motor and front suspension out to have the frame straightened. Also, the heat shielding was removed from the engine bay, and the fender came off. If you take a good look at the way the front frame members and shock towers are made, how thin the sheet metal is (and where it flexed and bent on my car), that its all just spot welded together - its amazing these cars hold together as well as they do (it looks weak). So, I will be adding a STB when rebuilding the car.
Depending on your type/level of driving you may or may not notice anything with adding a STB. I would think that for street use on street tires, you will never corner hard enough to deflect the shock towers enough to feel a difference in handling. In auto-x, DE, and racing, its quite possible that a car with big, fat R-compound tires, upgraded suspension, etc may be able to corner hard enough to noticeably deflect the shock towers. If that’s the case, then the car/driver could potentially benefit from a STB. "
12-27-2016, 11:30 AM
#4
Bimmerworld recently tried to figure out how much the strut towers moved on a SpecE46 race car at VIR. They were able to actually gather data and make some conclusions. It was obvious from the data that the strut towers do deflect a good amount but this was in a track scenario with a fully prepped race car.
http://news.bimmerworld.com/is-a-strut-brace-worth-it/
http://news.bimmerworld.com/is-a-strut-brace-worth-it/
12-27-2016, 01:37 PM
#5
Three Wheelin'
Interesting Van!
----
STOLEN (I stole this):
"Originally Posted by Oddjob
Ive been equally skeptical of any single modification that is marketed as a “big” improvement. But here is my current thinking on Strut Tower Bars.
Stiffening up the chassis, to reduce chassis flex probably has different effects on handling characteristics than does changing spring rates and sway bar settings.
Chassis stiffening can be accomplished by several means and to several levels of severity. Installing a roll cage (various types from bolt-in to custom welded in) all the way up to seam welding the body panels will stiffen a car up. Although it can alter the handling characteristics of the car because there is less body flex to account/compensate for with other suspension settings and setups, I would not necessarily consider this tuning the suspension.
With the front shock towers, the concern is that the outside shock tower deflects outward under corner loading. So if that is the case, it will change the camber on the outside wheel to a more positive wheel angle. Depending on the initial camber setting, this could reduce grip. So in theory, if the strut tower movement is reduced/limited by adding a STB, it could keep the alignment settings from deflecting (outside of the change inherent to a McPherson strut), which could actually make the car turn-in better (…?).
Now how much does a non-supported shock tower deflect? Who knows? How much does that deflection adversely affect handling? Does a STB offer that much chassis stiffening to actually improve handling?
I don’t know. Just like I don’t know how much (quantitatively) a full cage stiffens a chassis or how much seam welding does. Some people say you can really feel the difference, others say you cannot.
Keep in mind that the frame design of these cars goes back to the 924 in the early-mid 70’s. I don’t think the tub of the car was ever really altered/reinforced since that initial design. Porsche never intended the street cars to be run with solid bushings, 500 lb/in springs, 18” 245/285 Hoosiers. In a DE/Race application, my guess is that there probably is quite of bit of body flex - e.g. Ive seen a rear quarter window shatter on a 944S2 during a race practice.
When the factory did race the cars, they installed a strut brace (in the Turbo Cups and S2 Club Sports). And take a look at Jason B’s 968TRS and see the weld-in cage that the factory installed. See the pick-up points that the factory reinforced. They ran roll bar tubing out through the firewall to the shock towers and also used a STB to reinforce them. My guess is that the factory felt there must be some movement there in racing applications.
I was forced off track at my last club race and my car hit a berm. The right front shock tower was pushed up and inward. I pulled the motor and front suspension out to have the frame straightened. Also, the heat shielding was removed from the engine bay, and the fender came off. If you take a good look at the way the front frame members and shock towers are made, how thin the sheet metal is (and where it flexed and bent on my car), that its all just spot welded together - its amazing these cars hold together as well as they do (it looks weak). So, I will be adding a STB when rebuilding the car.
Depending on your type/level of driving you may or may not notice anything with adding a STB. I would think that for street use on street tires, you will never corner hard enough to deflect the shock towers enough to feel a difference in handling. In auto-x, DE, and racing, its quite possible that a car with big, fat R-compound tires, upgraded suspension, etc may be able to corner hard enough to noticeably deflect the shock towers. If that’s the case, then the car/driver could potentially benefit from a STB. "
----
STOLEN (I stole this):
"Originally Posted by Oddjob
Ive been equally skeptical of any single modification that is marketed as a “big” improvement. But here is my current thinking on Strut Tower Bars.
Stiffening up the chassis, to reduce chassis flex probably has different effects on handling characteristics than does changing spring rates and sway bar settings.
Chassis stiffening can be accomplished by several means and to several levels of severity. Installing a roll cage (various types from bolt-in to custom welded in) all the way up to seam welding the body panels will stiffen a car up. Although it can alter the handling characteristics of the car because there is less body flex to account/compensate for with other suspension settings and setups, I would not necessarily consider this tuning the suspension.
With the front shock towers, the concern is that the outside shock tower deflects outward under corner loading. So if that is the case, it will change the camber on the outside wheel to a more positive wheel angle. Depending on the initial camber setting, this could reduce grip. So in theory, if the strut tower movement is reduced/limited by adding a STB, it could keep the alignment settings from deflecting (outside of the change inherent to a McPherson strut), which could actually make the car turn-in better (…?).
Now how much does a non-supported shock tower deflect? Who knows? How much does that deflection adversely affect handling? Does a STB offer that much chassis stiffening to actually improve handling?
I don’t know. Just like I don’t know how much (quantitatively) a full cage stiffens a chassis or how much seam welding does. Some people say you can really feel the difference, others say you cannot.
Keep in mind that the frame design of these cars goes back to the 924 in the early-mid 70’s. I don’t think the tub of the car was ever really altered/reinforced since that initial design. Porsche never intended the street cars to be run with solid bushings, 500 lb/in springs, 18” 245/285 Hoosiers. In a DE/Race application, my guess is that there probably is quite of bit of body flex - e.g. Ive seen a rear quarter window shatter on a 944S2 during a race practice.
When the factory did race the cars, they installed a strut brace (in the Turbo Cups and S2 Club Sports). And take a look at Jason B’s 968TRS and see the weld-in cage that the factory installed. See the pick-up points that the factory reinforced. They ran roll bar tubing out through the firewall to the shock towers and also used a STB to reinforce them. My guess is that the factory felt there must be some movement there in racing applications.
I was forced off track at my last club race and my car hit a berm. The right front shock tower was pushed up and inward. I pulled the motor and front suspension out to have the frame straightened. Also, the heat shielding was removed from the engine bay, and the fender came off. If you take a good look at the way the front frame members and shock towers are made, how thin the sheet metal is (and where it flexed and bent on my car), that its all just spot welded together - its amazing these cars hold together as well as they do (it looks weak). So, I will be adding a STB when rebuilding the car.
Depending on your type/level of driving you may or may not notice anything with adding a STB. I would think that for street use on street tires, you will never corner hard enough to deflect the shock towers enough to feel a difference in handling. In auto-x, DE, and racing, its quite possible that a car with big, fat R-compound tires, upgraded suspension, etc may be able to corner hard enough to noticeably deflect the shock towers. If that’s the case, then the car/driver could potentially benefit from a STB. "
He is also the former caretaker and long time owner of my low mile, street driven '89- 951 - M030 in Satin Black Metallic. He is a VERY good racer, an excellent mechanic, a knowledgeable and likeable fellow.
I do know this: he and his Dad put together some of the most fearsomely competitive cars and ran them at our local Porsche Club D/Es and autocrosses as well as Club Raced their product on a high speed 3 mile asphalt and macadam track.
Trust what wisdom this guy imparts; a fool he is NOT
Jim, if you read this, please say a few words and introduce yourself
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12-28-2016, 01:50 PM
#8
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Join Date: Jan 2014
Location: Near Atlanta GA
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^+1. My 90 S2 Cab with a double floor pan was like driving a flying carpet after driving my 951s. After strut and caster block braces were installed, handling was significantly improved.
12-28-2016, 05:22 PM
#9
Drifting
That's the thread that gave us our chumpcar team name. WOT racing
http://www.924board.org/viewtopic.ph...0242770aeeb262
12-29-2016, 03:26 PM
#10
Race Director
12-29-2016, 08:51 PM
#11
Rennlist Member
Thanks Don, but I can't live up to your compliments.
Noah - where did you find that post? Has to be from 10+ years ago since the wreck mentioned was in 2005.
Aglift - interesting link, thanks for that.
As with Sam and Van, I have measured the tower deflection when a 944 is lifted, and the towers spread at least 1/8" when unloaded. I recall measuring up to 3/16" and I think Chris White also confirmed numbers at least that or higher.
The Turbo S triangular supports in front of the towers are an interesting addition. I can't say I know that they were installed to reduce shock tower movement or if they were intended to stiffen the frame rails in front of the shock towers due to sway bar loading.
Noah - where did you find that post? Has to be from 10+ years ago since the wreck mentioned was in 2005.
Aglift - interesting link, thanks for that.
As with Sam and Van, I have measured the tower deflection when a 944 is lifted, and the towers spread at least 1/8" when unloaded. I recall measuring up to 3/16" and I think Chris White also confirmed numbers at least that or higher.
The Turbo S triangular supports in front of the towers are an interesting addition. I can't say I know that they were installed to reduce shock tower movement or if they were intended to stiffen the frame rails in front of the shock towers due to sway bar loading.
12-29-2016, 09:45 PM
#12
Rennlist Member
They are "in plane" with the shock towers/frame rails - so they do nothing to stiffen what a strut tower brace does (which is perpendicular to that plane).
12-29-2016, 10:19 PM
#13
Rennlist Member
Agreed. My comment above was a noncommittal response to Murray's question. My actual belief is that they were intended to stiffen the front frame rails in reaction to the forces from the swaybar mounting brackets. But I can't prove that. They were first added to the 87 Cups when the 30mm front sway bar was put in use.
Last edited by Oddjob; 12-30-2016 at 12:09 AM.
12-31-2016, 12:22 AM
#15
Three Wheelin'
( Add humility to that list of accolades about Jim ..... )
And Thanks again for a GREAT 951. I do feel very privileged to be it's current steward and am thankful you gave me that opportunity as well.
How is progress coming on your CUP car ? Will we see it at an upcoming event ?
And Thanks again for a GREAT 951. I do feel very privileged to be it's current steward and am thankful you gave me that opportunity as well.
How is progress coming on your CUP car ? Will we see it at an upcoming event ?