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      04-26-2015, 02:08 PM   #133
fe1rx
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Quote:
Originally Posted by KevinK2 View Post
I bow to your excellent SAE quality write up, with excellent images to convey your thoughts ... one of the best write-ups I have encountered. But, we need to talk about some swaybar tech. In calculating the twist, you used J = pi r^4/4, but the correct value is pi r^4/2. So you have stiffened the calculated stiffness by a factor of 2. But even so, you were still close to the rate of the bench test, which the Puhn equation is based on. We ran ito this on the Mazdaspeed6 forum, where the measured rate was about 1/2 the calculated rate (you would have the same issue with the proper J used) :
http://www.mazdaspeedforums.org/foru...ml#post2779496 Lower on this page is Phate's bench test set-up.
You are correct. I got the answer I was looking for (incorrectly, thinking that bushing deflection and arm bending were relatively insignificant effects) so didn't dig any deeper.

Testing is definitive. I did the math to be able to estimate the stiffness for a hypothetical different bar. That is certainly suspect now. A factor of 2 correction for arm bending and bushing deflection isn't appropriate for a wide range of bar diameters, because bushing deflection will become more significant for stiffer bars.

The Puhn formula is only for a specific bar shape, never found in street cars.

Quote:
Originally Posted by KevinK2 View Post
Finally, you must think of the difference between the Bench Test / Puhn formula, and being in a corner. The Formula reflects a single wheel hit on the road, where the center of the bar is at about 1/2 the bar twist angle. In a corner, the bench test displacement is split between the lever going up on the outer side, and down on the inside by the same amount. This means the center of the bar has no rotation. Bottom line is you multiply the Puhn/bench rate by 2X to get the stable corner rate.
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.

I am using OptimumG's "magic number" spreadsheet which takes care of that math.
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      04-26-2015, 03:09 PM   #134
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Quote:
Originally Posted by fe1rx View Post
.... Testing is definitive. I did the math to be able to estimate the stiffness for a hypothetical different bar. That is certainly suspect now. A factor of 2 correction for arm bending and bushing deflection isn't appropriate for a wide range of bar diameters, because bushing deflection will become more significant for stiffer bars.
The Puhn formula includes the arm bending, and you could add that to your calculated deflection, simple (PL^3)/3EI , with L = C from Puhn.

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:
The Puhn formula is only for a specific bar shape, never found in street cars.
I have owned several cars where the shapes covered by puhn were identical to the actual bar ( mazda6 F&R bar, Rx7 FD F&R bars). But you have a point in that newer cars tend to have more curves in them esp rear bars in AWD, and they become more 3 dimensional vs the Puhn 2-D types.

[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:
I am using OptimumG's "magic number" spreadsheet which takes care of that math.
The bar will always have equal and opposite forces at the endlinks. I'd be interested in how significant jacking is in the case of your car, in terms of weight transfer bias.
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Last edited by KevinK2; 04-26-2015 at 03:16 PM.
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      04-26-2015, 03:35 PM   #135
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Quote:
Originally Posted by KevinK2 View Post
The factor of 2 correction has nothing to do with arm bending.
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, 05:59 PM   #136
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Quote:
Originally Posted by fe1rx View Post
I was referring to the implicit factor of 2 "correction" in my formula based on the incorrect moment of inertia calculation I made.
I don't think that was how the statement I quoted read, but OK.

Quote:
In other words, my estimates for other hypothetical bar stiffnesses, based on similar geometry but different diameters, is invalid.
Right. But to repeat what I quoted:
Quote:
Originally Posted by fe1rx:
.... Testing is definitive. I did the math to be able to estimate the stiffness for a hypothetical different bar. That is certainly suspect now. A factor of 2 correction for arm bending and bushing deflection isn't appropriate for a wide range of bar diameters, because bushing deflection will become more significant for stiffer bars.
I had mentioned that for the Mazdaspeed6 24mm front bar Phate tested, it turned out the measured rate was about 1/2 the Puhn calculated rate ( no bushing flex ). From that very limited data, I made a simple, emprical formula to adjust the calculated rate for oem bushing flex, where ratio "R" I explained earlier: Corr = 1/R^1.35 . To some degree, bushing size will increase with the bar dia, but stiffness is strongly related to the bar area moment of inertia, ie (D1/D2)^4 for solid bars, and bushing stiffness is likely proportional to the D^2. Could you check if it applies to your measured vs calculated stiffness? I know you tuned the oem bar parameters to get full agreement with the measured, including the factor of 2 for corner rate by mistake. Perhaps you have another way to adjust the Puhn calculated stiffness to include the ridgid body bar end displacement due to oem bushing flex, and urethane bushing flex?

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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Last edited by KevinK2; 04-26-2015 at 06:18 PM.
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      04-26-2015, 09:21 PM   #137
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Quote:
Originally Posted by KevinK2 View Post
I had mentioned that for the Mazdaspeed6 24mm front bar Phate tested, it turned out the measured rate was about 1/2 the Puhn calculated rate ( no bushing flex ). From that very limited data, I made a simple, emprical formula to adjust the calculated rate for oem bushing flex, where ratio "R" I explained earlier: Corr = 1/R^1.35 . To some degree, bushing size will increase with the bar dia, but stiffness is strongly related to the bar area moment of inertia, ie (D1/D2)^4 for solid bars, and bushing stiffness is likely proportional to the D^2. Could you check if it applies to your measured vs calculated stiffness? I know you tuned the oem bar parameters to get full agreement with the measured, including the factor of 2 for corner rate by mistake. Perhaps you have another way to adjust the Puhn calculated stiffness to include the ridgid body bar end displacement due to oem bushing flex, and urethane bushing flex?
Phate's bar is very far from the idealized Puhn bar. Isn't that where most of the discrepancy lies?

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:
Originally Posted by KevinK2 View Post
Most important, I think you did a great piece of engineering on this thread, on topic with the Ohlins install.
Thanks for that.

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, 11:10 PM   #138
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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, 11:56 PM   #139
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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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      04-27-2015, 12:13 AM   #140
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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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      04-27-2015, 03:35 AM   #141
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Quote:
Originally Posted by fe1rx View Post
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:

BEHIND THE SCENES
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 .
Nice work, very interested in the sway bar experiments, still running the OEM front bar from memory? It's interesting to note that @Orb went from the H&R bars to the M3/1M bar rates when running a similar spring rates albeit with KW dampers.

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, 04:04 AM   #142
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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, 02:02 PM   #143
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Quote:
Originally Posted by KevinK2 View Post
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.

.
Good to know. Coincidentally, that is exactly what I used just a couple of days ago up front (rear I installed dry of course). I considered Permatex's ceramic solid brake lube, but noted the Powerflex urethane shock top mounts I got came with a "copper grease" that looked very much like a traditional anti-sieze thread compound, so that is what I used.
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      04-27-2015, 02:10 PM   #144
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Quote:
Originally Posted by _Ryan_ View Post
Nice work, very interested in the sway bar experiments, still running the OEM front bar from memory? It's interesting to note that @Orb went from the H&R bars to the M3/1M bar rates when running a similar spring rates albeit with KW dampers.

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?
Yes I have the OEM front bar still.

A back to back test would be good if I can find a donor.
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      04-27-2015, 02:14 PM   #145
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Quote:
Originally Posted by John_01 View Post
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?
BMW dust boots. Not durable unfortunately.

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, 12:13 PM   #146
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Quote:
Originally Posted by fe1rx View Post
... I have made a 10 mm high spacer to go between the strut and the knuckle, which raises the lower spring perch the same amount relative to the tire

...The spacer is keyed to maintain the indexing of the strut and knuckle.

... With a 10 mm spacer, the strut is still fully secured by the knuckle. Taller than this would begin to reduce the support, and it would require re-routing the ABS cable. At 10 mm I believe the effect on brake hose routing and anti-roll bar end link geometry is small enough to be negligible.

... The other part of my solution is my custom camber plates, which are 5 mm taller than the GC plates they replace. You could achieve the same thing by putting a spacer on top of your camber plates.
Based on your experimenting, would you recommend welding a keyed tab on the strut tube to address rake I ended up with my Swift Spec-R springs, Bilstein B8 dampers, GC camber plates, Dinan Rear Shock Mounts?

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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      04-28-2015, 12:43 PM   #147
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Quote:
Originally Posted by fe1rx View Post

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
fe1rx, thanks for all of the informative threads you contribute to this forum.

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, 07:57 PM   #148
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Quote:
Originally Posted by dcaron9999 View Post
Based on your experimenting, would you recommend welding a keyed tab on the strut tube to address rake I ended up with my Swift Spec-R springs, Bilstein B8 dampers, GC camber plates, Dinan Rear Shock Mounts?

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?
Spacer on the topside of the camber plate might allow 5-8mm? From memory the turner reinforcement plates are around 5mm thick, could be an easy "slip on" test.

I'll wait for the guru
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      04-28-2015, 08:08 PM   #149
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Quote:
Originally Posted by dcaron9999 View Post
Based on your experimenting, would you recommend welding a keyed tab on the strut tube to address rake I ended up with my Swift Spec-R springs, Bilstein B8 dampers, GC camber plates, Dinan Rear Shock Mounts?

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?
I agree with your local shop. Welding a strut or a shock is not a good idea.

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, 08:14 PM   #150
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Quote:
Originally Posted by houtan View Post
fe1rx, thanks for all of the informative threads you contribute to this forum.

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.
I am glad you are enjoying this thread.

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, 08:40 PM   #151
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Quote:
Originally Posted by fe1rx View Post
I am glad you are enjoying this thread.

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.
Is there not even a weight advantage?
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      04-28-2015, 09:01 PM   #152
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Quote:
Originally Posted by Suprgnat View Post
Is there not even a weight advantage?
Yes, but even I can't convince myself that is why I changed them. These are grams of course:

Name:  OE Rear Upper Arm Weight.JPG
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      04-28-2015, 09:05 PM   #153
Suprgnat
German cars and French tires.
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Originally Posted by fe1rx View Post
Yes, but even I can't convince myself that is why I changed them. These are grams of course:

Attachment 1200595

Attachment 1200594
I'll take it, if only to justify my own modding insanity.
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      04-28-2015, 09:07 PM   #154
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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.
Speaking of looking good, any intention of marketing your toe arms?
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