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Join Date: Dec 2002
Posts: 2
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roll bar question
Hi all: soon I will be taking the rear seats out of my 911 in effort to lighten up the overall car. It was suggested to me to also put in a rear roll bar - I have one available to me fairly cheap. This rollbar is just the rear - not a full cage. My question is will the rear rollbar stiffen up the chassis and/or body, thus becoming a benefit aside from safety, or is it simply a matter of taking out weight and replacing it with other weight?
TIA 
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12-10-2002, 11:02 PM
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You do not have permissi
Join Date: Aug 2001
Location: midwest
Posts: 39,985
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I can't say that I have any knowledge on the issue, but if it's for track use you may need a full cage to comply with regulations(??).
Also something to consider is that the roll bar will go behind the drivers seat in front of the engine wall which already is a cross brace for the chassis. But then again, as those AX super slippery 914'ers know, weight in the middle doesn't count 
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12-11-2002, 01:01 AM
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If it is just a 4-point roll bar (2 floor mounts behind the seat and 2 more on the rear bulkhead) and your car is a couple or a targa, It won't add significantly to the chassis stiffness. Basically the mounts are too close to each other lenghtwise on the car to do anything. Essentially you are only bracing about 20% of the car's wheelbase, and it is not even a particulary flexible portion since it is where the B-Piller is. In general the weakest area of a car's chassis is the door area as well as the front and rear clips. A 4 point bar doesn't affect any of these. While it will help somewhat in a roll-over, once again, it won't do much since the forces are only being spread across 4 points rather then 6, 8 or even more in a full roll cage. So there is a good chance that the bar's mounts could just poke through the floor or bulkhead.
In the case of a cab, it's better then nothing as far as stiffness or protection, but once again not a big improvement. Note that the SCCA doesn't consider a 4 point bar acceptable for any competition (such Track use or Rallying) except for solo racing around cones.
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John '69 911E "It's a poor craftsman who blames their tools" -- Unknown "Any suspension -- no matter how poorly designed -- can be made to work reasonably well if you just stop it from moving." -- Colin Chapman Last edited by jluetjen; 12-11-2002 at 05:21 AM.. |
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12-11-2002, 05:15 AM
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Join Date: Nov 2001
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jluetjen,
since you are bringing up this subject, what is the SCCA requirement for tubing sizes? I'm thinking of using 4130 tubing, but can't find the SCCA rules posted anywhere... |
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12-11-2002, 05:54 AM
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Unfortunately the SCCA doesn't post its rules on-line. The good news is that I've transcribed the SCCA's roll cage requirements already on to this BBS, you might want to check out this thread. It has the spec's per my 2001 GCR. Since I'm not racing now I didn't buy the 2002 GCR, but the 2003 version should be out starting 1/2/03. This shouldn't be a big deal since the SCCA doesn't change it's cage spec's very often. I think that it will answer your question.
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John '69 911E "It's a poor craftsman who blames their tools" -- Unknown "Any suspension -- no matter how poorly designed -- can be made to work reasonably well if you just stop it from moving." -- Colin Chapman |
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12-11-2002, 06:09 AM
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Join Date: Nov 2001
Posts: 59
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This is what I needed. Thanks!
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12-11-2002, 06:24 AM
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1969 Porsche 911E 2.0 E
