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04-26-2015, 02:09 PM | #133 | |||
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The factor of 2 correction has nothing to do with arm bending. I mentioned a factor of 2 necessary to go from the puhn bench test equation, to a cornering condition, assuming any jacking effect is negligible. I also mentioned that in our case of lever hole and bushing positions on the bar, we were off in our bench test stiffnessby a factor of ~2 on the soft side. Sorry for the confusion. Quote:
[quote]That assumes that there is no jacking at the corner in question and the inside wheel's "up" matches the outside wheel's "down". Better, I think, to convert the bar stiffness to be a function of roll angle rather than one-wheel bump travel.[quote] I think the Puhn formula is fine as is. Jacking is a function of suspension type and roll center positions, and should be delt with separately, or in a reliable software package (OptimumG). No one has likely experience jacking as I have, with rear swing arms on my old Triumph. In an autox, the scenery in the rear view mirror changed to blue sky as the rear jacked on a tight corner. That was fixed by having trivial rear roll stiffness on a swing-spring upgrade. The bar's stiffness does not change due to jacking. Quote:
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tracked cars, 68 Triumph GT6, 81 Porsche 924T, 93 Rx7 Last edited by KevinK2; 04-26-2015 at 02:16 PM.. |
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04-26-2015, 02:35 PM | #134 |
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I was referring to the implicit factor of 2 "correction" in my formula based on the incorrect moment of inertia calculation I made.
In other words, my estimates for other hypothetical bar stiffnesses, based on similar geometry but different diameters, is invalid. |
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04-26-2015, 04:59 PM | #135 | |||
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There is also the possibility that at higher cornering G's, the load could be beyond the loads we tested, and the bushing will stiffen up. Most important, I think you did a great piece of engineering on this thread, on topic with the Ohlins install. .
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tracked cars, 68 Triumph GT6, 81 Porsche 924T, 93 Rx7 Last edited by KevinK2; 04-26-2015 at 05:18 PM.. |
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04-26-2015, 08:21 PM | #136 | ||
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Regarding a more precise method to account for bushing flex - I don't have one, nor have I characterized the bushing stiffness. It is simpler to bench test the bar with the intended bushings (assuming, of course, that you have it in hand). Quote:
A related comment: I have noticed that rubber bushings and bars want to stick together (urethane too, for that matter). Lubricating seems to work for a while (perhaps you have found a miracle lube that lasts well) but I am inclined to lubricate the bushings annually. H&R have textile lined bushings that supposedly dry lube the connection. My rear bar is H&R now so I will be interested to see how the lubrication properties stand up. |
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04-26-2015, 10:10 PM | #137 |
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2015
Well, the car finally saw daylight today and moved under its own power after a winter of tweaking. Here is how things have changed over the winter:
BRAKES: New dust boots all around. New stainless braided (Techna-Fit) brake hoses all around (because I figure 7 years was old enough for the OE hoses). Brakes bled with Castrol SRF. DRIVELINE: Red Line MTL D6 ATF transmission fill. Red Line 74W90 GL-5 Gear Oil differential fill. Bit the bullet and did the CDV delete (despite my general skepticism about the benefit). ENGINE: Did it myself walnut shell blast of my intake valves. http://www.1addicts.com/forums/showthread.php?t=1091813 REAR SUSPENSION 1) Installed a 20 mm H&M rear anti-roll bar. 2) Installed TRW upper arm and guide arm. 3) Installed custom rear toe arm. http://www.1addicts.com/forums/showt...1079383&page=2 4) Installed Powerflex upper shock mount. 5) Changed my rear springs from Swift 120 N/mm to 140 N/mm. FRONT SUSPENSION 1) Installed custom built camber plates and shock spacers to adjust ride height and reduce spring preload (documented earlier in this thread). 2) Installed new Swift Z65-176-060 (60N/mm) front springs to replace last-year's springs, which had been coil bound and had lost some of their original height. TIRES Last year's NITTO NT01s are toast and although I liked them they didn't last as long as I has hoped, and they are difficult to find in Canada. In fact, this Spring I was told that there were only 4 in my size in Canada and they can't be imported from the US (WTF is Nitto thinking?). Not a great idea to buy a tire for which spares are not available, so I selected to run RE-71Rs in 235/40R18 on my Apex ARC-8 8.5" x 18" wheels (square setup). I am not sure how these are going to survive track abuse, but wow are they sticky when cold. Definitely a step up from the ZII tires I used as my alternate last year. BEHIND THE SCENES 1) I had my Ohlins shocks (and an OE rear shock) tested on a Roehrig 2VS shock dyno (will report on the results later). 2) I spent a lot of effort measuring the suspension pickup point locations for the purpose of kinematic modelling of the suspension. I am trying to track down a fully functional copy of WinGeo3 for that purpose (but with the death of Bill Mitchell, this software is no longer supported). Anyone with a fully functioning copy please PM me. 3) I kept my last year's ride heights but have tweaked my camber and toe settings. With the stiff rear bar I expect less overall roll angle so have reduced front and rear camber each by 0.2 degrees. At the rear I have gone from a touch of toe out to zero toe. NEXT 1) Some instrumented skid pad testing to see if I have reduced limit understeer (by the use of a bigger rear bar and by reducing rear compliance steer with the stiffer suspension arms). 2) I am contemplating putting a staggered set of Max Performance Summer tires on my alternate wheels so I can save my sticky rubber for the track. That will let me investigate the effect of staggered tires vs. square on understeer gradient with actual measured data. Anyone interested in crowd-funding that experiment let me know . |
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04-26-2015, 10:56 PM | #138 |
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Please let us know your impressions of the RE-71Rs on track and on street! I'd be very inclined to give them a go if they are quieter on the street than the ZIIs have been.
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04-26-2015, 11:13 PM | #139 |
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That rear sway bar on the MS6 is ridiculous, and the tight space it fits in, limits the upgrade size to just 1 mm. That is why it's on the bench, because it was so far off the Puhn 2D geometry. I got Phate started on a new, 2D design that hangs down a bit, but will allow much bigger increases in both F & R bar stiffnesses. EDIT: Most of his reported data and comparisons with Puhn's equation is based on testing the more 2D front bar.
The bars in my 93 Rx7 are close to 2D, and Puhn works well. racingbeat RX7 Sway Bars Fabric lined rod-end bearings have been around a long time. The H&R have a version of this co-molded as an integral bushing, then split for assembly. The only issue I see is that the rubber is not a good support for the slick liner. There are very thin DU bushings designed to be pressed into a metal housing: metal-polymer DU bearing . But I'm sure H&R have done their testing. I have found a proper lubricant that I apply once .. no grease fittings. Since the relative motion is very slow, and an oscillation, it falls into the case of "boundary lubrication" where no oil film is created from a grease or oil. It's Permatex anti-seize paste type lubricant (for bolt threads). The solids provide low friction. Never a squeak, even on the old GT6 with split aluminum bushings up front, and at the rear where I designed and fabricated the 5 way adjustable 9/16" dia bar. Car saw 3 yrs autox (last 2 I won my class), and 5+ years of HPDE's. No squeak, no wear. .
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tracked cars, 68 Triumph GT6, 81 Porsche 924T, 93 Rx7 Last edited by KevinK2; 04-27-2015 at 10:35 AM.. |
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04-27-2015, 02:35 AM | #140 | |
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In relation to the staggered or square debate, are you able to test back to back with borrowed rims via your local club prior to investing? |
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04-27-2015, 03:04 AM | #141 |
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Are your new brake dust boots the same as the stock ones, or have you found something more durable?
Are you planning to get a LSD to go with these mods? |
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04-27-2015, 01:02 PM | #142 | |
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04-27-2015, 01:10 PM | #143 | |
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A back to back test would be good if I can find a donor. |
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04-27-2015, 01:14 PM | #144 | |
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I do see an LSD as the next mod. I am definitely sacrificing some ability to get the power down at corner exit in the quest for mid-corner grip with my current setup, but that was a conscious choice. I subscribe to the "LSD as the last mod not the first" school of thought. |
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04-28-2015, 11:13 AM | #145 | |
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According to your stats, stock OE stock mounts are 70mm and GC camber plates are 44mm, so that is probably a large factor in the "slammed front". What Im aiming for is to lessen the front-rear rake (about +22mm in the rear) by displacing the small welded tab on the strut body downwards, or welding a new one below it, which will result in the strut sitting higher in the knuckle. I discussed this with a local shop who cannot guarantee he will not damage the strut with the high temperatures reached during the spot welding process. He wants me to sign a discharge before he does the work ... fe1rx: Would really appreciate getting your feedback or alternative plan to above?
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2011 X3 35i with M pack + 2011 135i w/6SPMT | 255 square tire setup | Quaife 3.46 LSD | Diff lock down bracket | Bilstein B8+Swift SpecR springs+H&R FSB | CDV delete | BMS Oil Tstat bypass | ER FMIC & CP | N54Tuning DP | GC Street Camber Plates | M3 FCA +guide rods+RSFB's+Tranny mounts | Manzo toe arms | Cobb Stg2 agressive tune | Hawk DTC70 brake pads | RB SS brake pistons | Goodridge SS brake lines | Custom brake cooling ducts
Last edited by dcaron9999; 04-28-2015 at 11:32 AM.. |
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04-28-2015, 11:43 AM | #146 | |
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I was getting an education reading your thread about M3 rear suspension arms, http://www.1addicts.com/forums/showt...1079383&page=2, and in that thread you mention there is no benefit to using the M3 rear upper arm since the ball joint and bushing are similar to the oe 135i. I noticed in this thread that you ultimately decided to install the M3 rear upper arm. I have both the M3 rear upper arm and guide rods installed, so I am interested in hearing why you decided to install the upper arm if you didn't feel there was a benefit. Did you gather some additional data? Thanks again for sharing all the research you do with us, we appreciate it.
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04-28-2015, 06:57 PM | #147 | |
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I'll wait for the guru |
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04-28-2015, 07:08 PM | #148 | |
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1) you can use my bushing approach (which I think is only good for 10 mm). 2) you can mount a spacer between the camber plate and the strut tower. |
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04-28-2015, 07:14 PM | #149 | |
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I installed the M3 rear upper arm because it is a much nicer looking part than the OE one. I needed to buy it to test it, so I might as well use it. My advice was intended for those that want to direct their budgets purely at function. I am mostly that way inclined, but sometimes you just have to go with what looks good. |
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04-28-2015, 07:40 PM | #150 | |
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04-28-2015, 08:01 PM | #151 |
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Yes, but even I can't convince myself that is why I changed them. These are grams of course:
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04-28-2015, 08:05 PM | #152 | |
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04-28-2015, 08:07 PM | #153 |
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04-29-2015, 09:44 AM | #154 | |
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