Modern trailing arms for the 914?, 986 carriers/calipers/e-brake, more adjustability, more tire? |
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Modern trailing arms for the 914?, 986 carriers/calipers/e-brake, more adjustability, more tire? |
horizontally-opposed |
Jan 26 2021, 12:21 PM
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#1
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Advanced Member Group: Members Posts: 3,431 Joined: 12-May 04 From: San Francisco Member No.: 2,058 Region Association: None |
I've been reviewing past discussions on these (links below) off and on, having test fit a 215/60R15 Pirelli P6000 on a 911R wheel into both rear fenders of my narrow-body 914. It seems doable, but it's going to take some massaging on the outer fender, custom spacers, and—maybe—narrowed trailing arms. Which got me to thinking about the current state of the 914 trailing arm, which is the same it's been since 1970.
Basically, those heavy, non-adjustable steel trailing arms are one of the very few things on the 914 that hasn't been addressed or evolved by the aftermarket. I'm running PMB-rebuilt trailing arms with PMB-rebuilt calipers, and can redo them again with reinforcements and/or some reshaping, but I wonder how hard would it be to do blade-type trailing arms of similar strength with less weight and/or more adjustment. Could a 911 spring plate, or a triangulated or otherwise reinforced version of it, be adapted? Looking at the basic design of the 914 arm, it doesn't look all that complicated, but I'm no engineer. EDIT: Possible use of a machined 986 wheel carrier, an aluminum casting by Brembo that incorporates the 986 e-brake and 986 four-piston caliper mounts, comes up later—a very interesting idea from @Chris914n6, particularly as the castings are available for $100-200ea used or new from Porsche. Bolting that carrier to a new steel trailing arm with a lower damper mount seems viable to me, but here to learn. The custom work to narrow factory 914 trailing arms looks extensive, but has been done by both @914timo and @sixnotfour as well as, it looks like, Rich Johnson. I could see doing it in the process of moving to 911 e-brakes and 986 2.5 brakes, maybe, but I wonder if a group buy might attract a 914 vendor we all want to support? Relevant threads: http://www.914world.com/bbs2/index.php?sho...p;#entry1247827 http://www.914world.com/bbs2/index.php?sho...ailing&st=0 http://www.914world.com/bbs2/index.php?sho...238144&st=0 http://www.914world.com/bbs2/index.php?sho...234391&st=0 |
914Toy |
Feb 2 2021, 11:17 AM
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#2
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Senior Member Group: Members Posts: 717 Joined: 12-November 17 From: Laguna beach Member No.: 21,596 Region Association: Southern California |
While repairing damage to my 914's passenger rear quarter caused by a texting driver crashing into it (IMG:style_emoticons/default/mad.gif) ,repairs required a good used replacement full quarter panel and trailing arm. I recall one "expert's" comment that the trailing arm strength and design included minimizing damage to the tub in the event of such damage. This worked for me. So, perhaps strengthening the trailing arms along with weight reduction should not be done for our street cars, but may be helpful for track cars.
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horizontally-opposed |
Feb 2 2021, 03:19 PM
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#3
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Advanced Member Group: Members Posts: 3,431 Joined: 12-May 04 From: San Francisco Member No.: 2,058 Region Association: None |
Pete While I find the topic intriguing I wonder what the real end game is. Tire technology has outpaced suspension design over the last 50 years. So now unless you racing competitively in auto crossing at the national level I would not worry about 10mm of sedition width. Slap on a set of DOT R compound tires, add a set of fender liners, and go drive… End game is: 1) "Right-sized" footprint: I've had virtually every 15-inch tire size that will fit into a narrow 914 under my car. Current rubber is Avon CR6ZZ, a vintage race/rally tire available in three compounds, so about as grippy as you'll get. 185/70 all around is just okay; with RS 2.7~ power, I'd like to run a similar tire package without resorting to M471 flares or a repaint. Suspect there are others in the same boat with 2.7s, 3.0s, 3.2s, etc 2) Performance and looks; 215/60 seems to me about right for what I am after in terms of performance, and I think it would also look great on the car. 225/50R16 also offers fantastic performance and looks great tucked into the back of a narrow 914. 3) Tire choice; 205/60R15 tire choice is far from great; factory tire sizes offer prospect of more availability & choice over the long haul; 195/65 & 215/60 or 185/70 & 215/60 offer period looks and at least three great options for the street. If there's space for 225/50R15 or 225/50R16 in the rear, unlocking some great R-compound tires, that's a bonus. My test fit suggests modified trailing arms and a bit of fender pull might make it work. 4) Cost to rebuild/modify old arms: Prospect of spending $2000-4000~ to redo another set of 50yo trailing arms with little to no technical upside isn't interesting. 911 e-brakes and aluminum calipers wasn't appealing, so I wanted to get some feedback from the community on whether the time has come for another option. Fully agree on rewarding vendors in the 914 community, and have sent a fair bit of business their way over the years, but perhaps a new trailing arm might be more profitable for them than modding old ones? Fortunately, smarter people than me (!) are spitballin' this now. Carbon was an early casualty due to setup costs as well as actually popping them (not to mention liability and potential inspection/longevity/etc), and I suspect Ti is out due to $$, too. While repairing damage to my 914's passenger rear quarter caused by a texting driver crashing into it (IMG:style_emoticons/default/mad.gif) ,repairs required a good used replacement full quarter panel and trailing arm. I recall one "expert's" comment that the trailing arm strength and design included minimizing damage to the tub in the event of such damage. This worked for me. So, perhaps strengthening the trailing arms along with weight reduction should not be done for our street cars, but may be helpful for track cars. Glad you raised this, as it was on my mind at one point. Worth paying attention to if there's a solution—as I'd far rather lose an arm than a car! Sorry for my mess on my pouring table but this is a PMB (E) modified strengthened trailing arm done 10 years ago. Weight 25.5 LB with 930 turbo Stub Axels, 911 early parking brake, Elephant Polly Bronze and well what you see. Bob B No apology needed! (IMG:style_emoticons/default/biggrin.gif) Another great input & data point. 25.5 with all that we see there is not bad, not bad at all. Maybe the goals shift to cost of upgrade ($2000-4000~ rebuild vs $250-500 custom spring plate + triangulation of some sort + used $100 986 carriers, etc) with any weight saved or additional clearance for a 215 or 225 tire as gravy. |
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