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Old 09-12-2018, 11:24 PM   #1
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GT3 LCA Build

I have been looking at GT3 style LCAs for some time and have wanted to model some up but have not had a part to look at until recently. Attached pictures are modeled using a stock GT3 inner and outer but with 14mm spherical bearings (monoballs) at both ends and Tarett style solid thrust bushings. I will build sets for both front and rear out of 7075 for the inner and outer arms and thrust bushings and 4340 for the monoball spacers.
Ideas, comments, corrections from the wealth of knowledge of the board would be great.
I look to do this over the next months for this winter’s project and will document the design, build, and install with you all.







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Old 09-13-2018, 09:33 AM   #2
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Nice work man! Don't forget the Litronic linkage.....some may want that.

For something like this, folks will want to see loads of testing..
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Old 09-13-2018, 11:05 AM   #3
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Very cool! I love innovation and someone trying do something new.

With that being said, have you done a cost breakdown yet? Materials + machining setup & hours + quality checks/inspection + assy + etc, etc.

I would send out the drawings to machine shops to get formal quotes (not estimates or ROM's, but real quotations) before investing much more time into anything. In my experience, I am always surprised at the (high cost) quotes that I get back.
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Old 09-13-2018, 11:21 AM   #4
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something like this might be less complicated to fabricate - no cnc, just welding ...

https://www.tarett.com/items/986-987-981-718-products/986-987-981-718-suspension/986-987-981-718-control-arms/pro-series-control-arm-kit-erp-lca-detail.htm
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Old 09-13-2018, 01:23 PM   #5
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A more custom or radical LCA design for the build was something I was not prepared to do from a time and testing perspective. Maybe after successfully building these a tube syle could be possible.

For this reason the inner/outer are modeled directly from the stock GT3 LCA dimensions to leverage Porsche factory engineering with the only difference being a larger 14mm spherical bearing in both ends. Fasteners will be 12.9 grade. 4340 spacers will be hardened.

From a cost view I am designer, machinist for the simpler parts (thrust bushing/monoball spacers), and assembler. Both my next door neighbor and my best friend's brother both own local machining shops where we will build the inners/outers for a few cases of beer and pizza.

I will also model different thickness spacers when I get my hands on a stock one to get the profile dimensions. Do any of you have knowledge of what the most useful thicknesses would be?

Jay, to incorporate a Litronic sensor, wouldn't one just need to get the a Litronic spacer?
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Old 09-13-2018, 04:53 PM   #6
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Im installing a set of these right now. Nice pieces with endless adjustment
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Old 09-19-2018, 04:27 PM   #7
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I have cleaned some stuff up to facilitate cutting, (chamfers instead of outside fillets and purely cosmetic profiles for example), and modeled the spacer and got the mating geometry good.

I added four ž” cuts 90 degrees from each other in the thrust bushing as I wondered how I would rotate the screwed together bushings to adjust caster without some tool. I imagined four because as the bushing rotates having more could be good as the tension arm might rotate over the cut if I only had one. In checking other bushing pictures, as far as I can determine only Elephant has a hex key cutout for what I think would be used for this purpose. I do not have any experience with adjusting caster bushings and don’t know if a cut for a tool to help rotate the bushing is really needed. I circled one of the four cuts in red in one picture. Anybody have any thoughts on whether the cuts could be useful or are they unnecessary?




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Old 12-05-2018, 07:09 PM   #8
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Finally getting some parts built. 1mm, 2mm, and 3mm shims waterjetted and now needs deburring and anodizing. 10mm and 15mm sheets going on next week with 5mm, 7mm, and 8mm to follow.

I sourced decent sized metric sheets to cut and have quite a few shims after anodizing if anyone needs some cheap.



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Old 12-17-2018, 05:48 PM   #9
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More shims...

15mm, 10mm, and 8mm...





Spherical bearing insert adapter bushings starting next week..
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Old 12-18-2018, 09:53 AM   #10
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Im installing a set of these right now. Nice pieces with endless adjustment
Nice stuff, but what the heck do they mean by: " this no compromise design the center geometry can also be adjusted to correct for lower ride heights."

On McPherson, when ride hight is lowered beyond the point where the LCA are vertical you will get a positiv (not good) effect on camber, also the roll center will become higher.
How will those Tarrett control arms compensate for that, Idonīt see that it is possible.

Educate me..
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Old 12-18-2018, 10:01 AM   #11
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not sure, but if your camber is controlled by extending/retracting the control arm, then you can use the inner eccentric to raise/lower the control arm inboard attachment point to compensate for changes in coil over length.
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Old 12-18-2018, 01:27 PM   #12
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they may also be referring to the use of shims to control anti-dive/squat on the diagonal control arms. perhaps some marketing fluff in there
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Old 12-18-2018, 02:03 PM   #13
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Originally Posted by Robert986 View Post
Nice stuff, but what the heck do they mean by: " this no compromise design the center geometry can also be adjusted to correct for lower ride heights."

On McPherson, when ride hight is lowered beyond the point where the LCA are vertical you will get a positiv (not good) effect on camber, also the roll center will become higher.
How will those Tarrett control arms compensate for that, Idonīt see that it is possible.

Educate me..

I believe they are referring to roll centre. I have not reviewed the component or its adjustments but you would have to be able to change the position pivot (up or down) points to affect roll centre position.

No one ever talks about this adjustment but theoretically it will have a massive influence on a vehicles handling during cornering as it is essentially the roll axis of the vehicle. Its position relative to the CG is what is critical. You want to aim the arm such that the roll centre is closer to the CG. This will yield a reduced roll moment.

Edit: I just had a look and they do mention roll centre at the very end of the description; I cant quite see but I would think the pivot position adjustment would some how be incorporated at the outboard end with a spacer of some sort
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